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Understanding oil absorption during deep-fat frying
Abstract
One of the most important quality parameters of fried food is the amount of fat absorbed during the process, which undermines recent consumer trends toward healthier food and low-fat products. In order to obtain a product with a low fat content, it is essential to understand the mechanisms involved during the frying process, so that oil migration into the structure can be minimized. To get such an understanding, this chapter briefly describes the frying process from technological and scientific perspectives. First, it gives a general overview of the frying process and describes the most important quality attributes of fried food. Thereafter, it centers on key nutritional aspects, particularly on the effect of excessive oil consumption on human health, oil degradation, and toxic compounds generation in fried food. Finally, this chapter discusses the most important factors affecting oil absorption, oil absorption kinetics, and different strategies that may be adopted to decrease oil content.
... Oil absorption directly impacts the increase in energy, one of the most significant transformations related to the frying process. Several factors related to the process and/or food, such as water content, crust microstructure, product geometry, frying time, temperature, and oil quality, can influence oil absorption [7][8][9]. The changes during frying affect the physicochemical, sensory, and nutritional parameters of food quality [10]. ...
... It is believed that the initial amount of water and solid content in the food are factors that can influence the absorption of oil [33]. However, oil absorption appears to be more closely related to moisture loss than to initial moisture, with the amount of oil absorbed being directly proportional to the moisture lost [7]. Furthermore, it has been suggested that oil absorption is greater when the contact surface increases and the product thickness decreases. ...
... The type of oil used also influences oil uptake by fried products; however, it may be more related to the quality of the oil [7,35]. Studies claim that the amount of unsaturated fatty acids in the oil can influence its absorption by food and that the fatty acid composition of oils is highly related to their viscosity and surface tension, affecting the wettability of oil and food during the frying process, heat transfer and mass transfer rate, drainage of oil during the post-frying and cooling phases, and, therefore, the oil content absorbed by the final products [36]. ...
The frying process changes can be desirable and undesirable, involving the physicochemical, nutritional, and sensory aspects, depending on the food and oil properties and the frying process. In this context, alternative flours emerge as a strategy for adding value to the food since they are rich in fiber, vitamins, and minerals, contributing to the variability of ingredients and the full use of food, including residues such as seeds and husks. This narrative review aims to gather current scientific data addressing the alternative flour coatings on breaded meat, mainly chicken, products to evaluate the effects on fried products’ nutritional value, physicochemical parameters, and sensory attributes. Scopus, Science Direct, Springer, and Web of Science search bases were used. This review showed that alternative flours (from cereals, legumes, fruits, and vegetables) used as coatings increase water retention and reduce oil absorption during frying, increase fibers and micronutrient content, which are not present in sufficient quantities in commonly used flours due to the refining process. These flours also reduce gluten consumption by sensitive individuals in addition to favoring the development of desirable sensory characteristics to attract consumers. Therefore, frying processes in oil promote a reduction in humidity, an increase in oil absorption and energy content, and a decrease in vitamin content. In this context, coatings based on alternative flours can reduce these adverse effects of the frying process.
... The power settings for microwave generators for the frying experiments are shown in Table 1. Industrial frying temperatures for French fries vary from 170 to 190°C (Pederson, Braich, Samoray, & Sloan, 2003;Strong, 1968;Bouchon, 2009), so we selected 180°C as the temperature for the oil. ...
... The 50% of moisture loss oc-curred in the first 1 min, and the drying rate began to decline as frying progressed (Fig. 3a). The reductions in the moisture loss rate and oil intake rate were mainly because of the starch gelatinization of outer surface and the formation of crust (Bouchon, 2009), which together slowed down heat and mass transfer. ...
... For example, at frying time of 5 min, 2.45 GHz microwaves resulted in the lowest moisture content and highest oil content in French fries, followed by dual-frequency microwaves, 5.85 GHz microwaves, and the control. More pores could be formed in the crust upon water removal with the addition of microwave energy (Bouchon, 2009;Liberty et al., 2019). Such pores determine maximum volumes Fig. 3. Changes of (a) moisture content (mean ± standard deviations) and (b) oil content (mean ± standard deviations) of potato strips during deep-oil frying (control) and oil plus microwave frying at different microwave frequencies (2.45 GHz, 5.85 GHz, andcombination of 2.45 and 5.85 GHz), n = 3. Zhou et al. ...
French fries are popular items in the diets of many countries, but the high oil content is a major health concern for consumers. Numerous novel frying techniques have been explored by the fast food service industry and the research community to address such concern. This research aimed to study the influence of microwave heating at two frequencies (2.45 and 5.85 GHz), both individually or in combination, in frying and post-frying on oil reduction in French fries. Results showed that microwave frying reduced the frying time by 30 – 40%, with equivalent product quality attributes in terms of oil content, color, and texture, as compared to deep-oil frying. Oil intake increased with increasing moisture loss during frying, regardless of frying methods. Post-frying was the key to oil reduction. Additional 60 s microwave heating after frying reduced the oil content by 18 – 23%. Compared to 2.45 GHz, microwaves at 5.85 GHz could produce French fries with significantly lower oil content (p ≤ 0.05) and better quality attributes such as color and texture. This study highlighted the potential of microwave heating to produce deep-fried French fries with lower oil content and better quality.
... This deterioration is due to the absorption of oils by fried foods that increases with the duration of the frying process. Indeed, the more the oil oxidizes, the more viscous it becomes, and the more it is absorbed by the food [8,9]. Therefore, several synthetic antioxidants including butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), and butylated hydroxytoluene (BHT) were explored to extend the shelf life of frying oils, to delay the formation of undesirable components, and to improve the sensory properties of fried products [10]. ...
... Different factors could cause this phenomenon: cooking temperature, the fried food/oil weight ratio, humidity, shape, and size of fried food [29]. Moreover, the oxidation of frying oil makes it very viscous and therefore easy to be absorbed by food [8,30]. ...
Fried foods and frying oil are subjects that warrant the attention of researchers because of their high consumption. Indeed, frying conditions make these oils very sensitive to lipid oxidation which deteriorates the quality and nutritional properties of the food. In this study, we examined the effect of rosemary extract (ROE), known for its high antioxidant activity, in soybean oil used to fry breaded butterfly shrimp, by measuring the induction period with OXIPRES, total polar material (TPM), peroxide index (PI), and free fatty acids (FFA). This evaluation was performed in comparison with control oils without antioxidants. The results showed a significant difference between the oils according to the analyzed parameters, especially in the final hours of frying. The treatment of the oil with rosemary extract effectively delayed its oxidation, having lower levels in all the oxidation markers that were analyzed. It was also found that rosemary extract is able to reduce oil consumption by fried foods. Therefore, ROE ensures soybean oil a high stability against oxidation and a longer shelf life, making it a good natural alternative to synthetic antioxidants.
... This might be because the characteristics of CHB1 was in a small piece, relatively dry meat and loosely packed inside, but still was able to remain in shape when frying. The lowest level of fat of CHB1 could be explained for the reason that those characteristics made moisture inside evaporate quickly and form an external hard shell (Bouchon, 2009;Kaczay, 2016;Liberty, Dehghannya, & Ngadi, 2019). CHB2, in triangle thick flat shape, was found high in moisture with less oil absorption. ...
... This resulted from CHB1 was using recipe differently from all cassava hash brown variations which were cooking with the same recipe. All variations from casava hash brown also found no significant difference in oily from CHB1because the small cassava pieces were packed tightly inside, that help to reduce oil absorption (Bouchon, 2009). HNTS6 and HNTS7 gave a better score in color closely resemble the color of CHB1 (golden color) because the steaming method gave a brightness lower than the boiling method, due to the colorant of cassava skin dissolve in the water while boiling, so the golden color of HNTS6 was satisfied with less time to production. ...
Consumer acceptance when substituting potato with Thai sweet cassava in frozen hash brown was assessed. The most popular commercial potato hash brown was selected as the benchmark. Results revealed consumer preferred small round 1 inch diameter with reduced oil absorption and crispy outside and soft inside. The optimal formula for hash browns was determined, replaced potato with sweet cassava and applied various alterations of cooking method and cooking time. Sweet cassava hash browns showed promise over the benchmark with the unique flavor of cassava, less salty taste and an acceptable level of greasiness. However, cassava hash browns contained high fiber levels that reduced consumer acceptance.
... determines the trend toward healthier food and low-fat products (Bouchon, 2009). The excessive consumption of oil, especially saturated fats and trans fatty acids, is a major threat to human health and can cause diseases such as high blood pressure, high cholesterol, coronary artery blockages, and obesity (DiNicolantonio et al., 2016;Siri-Tarino et al., 2010). ...
... Pre-frying treatments aim to reduce surface permeability due to the marked effect that crust microstructure has on oil absorption. However, the purpose of post-frying treatments is to remove surface oil before the suction of post-cooling begins (Bouchon, 2009). Hydrocolloids have, however, attracted considerable attention over the last decade for their use in inhibiting oil absorption (Kurek et al., 2017;Salehi, 2020). ...
There is a widespread use of deep‐fat frying in both domestic and industrial sections, and deep‐fat fried foods are extremely popular due to their taste, color, and crispy texture. Human health can be, however, seriously compromised by the excessive consumption of oil, especially saturated fats and trans fatty acids. The use of hydrocolloids in inhibiting oil absorption has garnered considerable attention. This study was therefore aimed to lower the oil absorption in eggplant rings during the deep‐fat frying process with the aid of Aloe vera gel coating. The effects of gel concentration (0%, 50%, and 100%), frying time (2, 5, and 8 min), and frying temperature (160°C and 180°C) on the oil uptake, moisture content, texture, color, and sensory properties of the eggplant rings were evaluated. The gel coating led to a decrease in oil uptake (up to 50%), hardness (up to 0.98‐fold), ΔE (up to 0.89‐fold), and overall acceptance (up to 0.85‐fold), and an increase in moisture content (up to 1.47‐fold) and lightness (up to 1.14‐fold) of the samples. The frying time and temperature also influenced the physiochemical and sensory properties of the eggplant rings. The sample coated with 50% gel and fried at 180°C for 8 min had lower oil content and water loss with the highest acceptance rate in terms of taste, color, odor, texture, and appearance. The Aloe vera gel could be, therefore, a good candidate with high nutritional and economic value to reduce oil uptake in fried food products. The sample coated with 50% gel and fried at 180°C for 8 min had lower oil content and water loss with the highest acceptance rate in terms of taste, color, odor, texture, and appearance. The Aloe vera gel could be a good candidate with high nutritional and economic value to reduce oil uptake in fried food products.
... e transfer of heat from oil to food gives rise to various chemical reactions which cause cellular and subcellular changes such as starch gelatinisation, crust formation, protein denaturation, moisture loss, oil uptake, and colour and flavour development. Mass transfer is explained as the evaporation of moisture from food during frying, which creates crevices or pathways in food for oil uptake first in the crust and then gradually to the crumb [2]. is makes oil uptake reduction, modelling, and distribution important quality parameters in fried foods. ...
... Penetrated surface oil (PSO), located in the crust of food, is oil suctioned into food at the cooling stage through a vacuum effect caused by the condensation of steam [7,8]. PSO is regarded as the most important of the three fractions because it contributes the most to the total oil uptake and is greatly influenced by the structural integrity, surface roughness, and permeability of the food crust [2]. An integral constituent of wheat flour dough is water, needed for hydration and activation of the gluten network; to achieve this, the right amount of water is needed [9]. ...
This study investigated oil distribution in two types of deep-fried dough products with two moisture levels (65 and 100 wt. %), two bran types (oat and wheat bran), and five bran concentrations (5-20%). The total oil content of fried products was categorised as surface oil (SO), penetrated surface oil (PSO), and structural oil (STO) using a spectrophotometric method. Moisture loss reduced (p<0.05) from 23.35% in the control to 15.19% fried batter (FB) and to 20% oat bran (OB), while a reverse trend was observed in the fried dough. Reduction of total oil from 0.43 g/g in the control to 0.38 g/g at 20% OB and 8% wheat bran (WB) was observed. At 15% OB and 20% WB, total fat reduced from 0.41 g/g in the control to 0.26 g/g of fried dough (FD). The trend STO < SO < PSO was observed in FD, while FB followed a SO < STO < PSO trend. This investigation indicated that oil uptake reduction in fried dough products is achievable through ingredient modifications. The method of oil distribution measurement used herein can be applied to other thick deep-fried food systems in the assessment of product quality.
... TPC is used to measure the oil degradation and quality, especially in frying application because of it affects the quality of the fried food (i.e. browning effect, oil uptake and shelf life) (Bouchon, 2009;Hammouda et al., 2019;Li et al., 2015). Similar to color, Table 3 Physicochemical characteristics of refined palm oil (aRPO) produced from AL-treated CPO during deep-frying. ...
... The higher uptake of the oil was possibly due to the higher TPC found in RPO than aRPO. Previous studies have shown that the oil absorbed by the food could be affected by the TPC as well as the oxidative and hydrolytic stability of the oil used (Bouchon, 2009;Rimac-Brnčić et al., 2004). ...
Deep-frying is a popular method for food preparation because it improves the taste and sensory of food. Among the vegetable oils, palm oil is one of the commonly used oils for deep-frying application. During deep-frying, some of the oil would be absorbed by the food and subsequently be consumed together with the food. Hence, the quality and stability of the oil used for deep-frying are of critical food safety considerations. To address this issue, we produced refined palm oil from crude palm oil which has been treated with an aerobic liquor (AL) generated from a palm oil mill. The result shows that the refined palm oil produced from AL-treated CPO (aRPO) has improved quality, in particular the 3-monochloropropane-1,2 diol ester (3-MCPDE) and the glycidyl ester (GE) reduced by 58% and 46%, respectively. After 30 cycles of deep-frying, the used aRPO contained 68% lower FFA content, 13% lower polar content, and 43% lower 3-MCPDE content compared to the conventionally produced refined palm oil (RPO). Furthermore, the aRPO has a higher smoke-point and a higher resistance to darkening compared to the RPO. As a result, the fries prepared using aRPO have lower 3-MCPDE content and they have a better appearance and were less greasy when compared to the fries prepared using RPO. Overall, AL-treatment of CPO is a feasible method to improve the quality and deep-frying performance of refined palm oil and it could readily be adopted by the industry because it is simple and sustainable.
... Through this study we analyzed the international and local food security practices in relation to cooking oil types in different cooking methods. Thus, we developed a hypothetical model of food security management system in usage of edible oil and oil-based products which can be used for a very comprehensive assessment of food preparation facilities instead of using the existing food safety standard alone [15][16][17]. ...
... which are affected to the food security system which consists of four pillars including: Availability, access, utilization and stability[17][18][19][20] (Figure 1). ...
In 2009, The World Summit on Food Security introduced four pillars of food security namely; availability, access, utilization, and stability. Food security could be substantially improved by increased investment and policy reforms. The ISO 22000:2005 family of international standards is one of leading food safety security management systems and it specifically addresses food safety management. The purpose of this study is to develop an extended framework of standards opposed to ISO 22000:2005 food safety standards considering one additional pillar in food security, which is food safety, with a special reference to edible oil and oil-based products. Among 745 Colombo Municipal Council (CMC) registered food preparation facilities, 75 facilities were selected as a stratified random sample. A self-administered online questionnaire was used to identify gaps in local food security practices in edible oil. Data analysis was performed using SPSS version 21 and characteristics of sample were analyzed using descriptive statistics. The results of the survey revealed that the Sri Lankan food preparation facilities are significantly behind in food security practices. Therefore, in addition to food safety management system, we suggest to include four pillars in food security systems into the existing food safety standard due to lack of food security practices in food preparation facilities. Considering the deviated areas in the practice, which were identified through our questionnaire, we developed a novel model of food security management system for a comprehensive assessment of food preparation facilities.
... Texture is one of the important quality aspects, and a crispy crust is an important factor in the sensory properties of French fries (Vickers and Bourne, 1976;Pedreschi and Aguilera, 2002;Salvador et al., 2009). Deep-fat frying can be defined as a process of drying and cooking through contact with hot oil (Farkas et al., 1996a;Bouchon, 2009). This process essentially consists of soaking the product in hot vegetable oil at a temperature above the boiling point of water, typically 150-180 • C. ...
... The water on the surface immediately starts to boil. In order for the flow of vapor to continue, sufficient water has to be able to migrate from the core of the food to the crust and the crust has to remain permeable (Farkas et al., 1996a;Farkas and Hubbard, 2000;Mellema, 2003;Bouchon, 2009). Due to evaporation, drying occurs at the surface and core of the French fries. ...
This study aimed to identify the microstructural parameters of the crust which can explain the crispness of French fries. The French fry microstructure was visualized by X-ray micro-computed tomography (XMT). Analysis of the images provided information on the pore size distribution, global porosity of the French fries and local porosity of the crust region. The results revealed that prefrozen French fries do not practically undergo any volume shrinkage during frying. The total porosity created in French fries corresponds to the volume of water loss during frying. The difference between hot-air fried and deep-fat fried French fries was mainly related to the pore diameter and pore size distribution in the crust. Principal component analysis between the sensory and morphometric parameters showed that the volume of small pores (diameter < 0.15 mm) and the span of the pore size distribution in the first millimetres of the crust correlated with the crispness of the product (r > 0.85, P value < 0.05). Thus, a French fry is crispier if the pores generated in the crust have a small median diameter (diameter < 0.2 mm), as well as a large dispersion of pore diameters.
... Deep-fat frying temperatures typically average 180 °C. In some cases, although this is unusual, 130 °C may be considered [13]. Note: C here carbon with 16 or 18 or more carbon chains with one/two/three double bonds at specific positions as mentioned, followed by n. [10,14] 1. Rapeseed oil, or Canola oil, is processed oil derived from rapeseed plants' seeds, necessitating elevated temperatures, pressure, and chemical agents during refining. ...
The use of edible oil is an integral
part of daily cooking. Different people have
different opinions about selecting edible oils
globally; however, regions, family trends,
individual choice, taste, flavor, availability,
and affordability are the factors in choosing
such oils. There is a growing scenario of such
edible oils as palm oil, followed by canola
and soybean oil in the global market. Indian
cooking practices exhibit notable variations
compared to other regions worldwide. One
key distinction is in the frequent heating of
oils during the process of stir-frying, which
leads to the degradation of essential
antioxidants such as vitamins E, A, B
vitamins, folate, etc. To mitigate exposure to
harmful substances, it is recommended to
refrain from consuming refined oils and lowsmoke-point- based oils as they tend to
undergo rapid degradation and possess
elevated levels of polyunsaturated fatty acids.
The edible oils with MUFA or PUFA are also
considered suitable for consumption. Finally,
blended oils have notable thermal and
oxidative stability, rendering them
indispensable in preserving the optimal
dietary balance of fatty acids. Overall, every
oil has significance, but blended oils would
perform better in the kitchen and keep health
sound. This study comprehensively reviewed
all the common cooking oils, particularly
popular and available in India. Every oil has
significance, but selecting the right oil for
cooking would be wise.
... The oil cannot fill the empty spaces as long as steam continues to be produced. The movement of oil can be characterized as Fat uptake in food during the process of frying [21] Content courtesy of Springer Nature, terms of use apply. Rights reserved. ...
Deep-fat frying is a widely discussed topic globally in the field of food processing due to the growing consumer demand. These foods are known for their appealing outer appearance, crispy texture, and rich taste. The increased consumption of deep-fat fried foods has raised concerns regarding potential health issues, as they are often high in calories and may contain unfavorable compounds formed during the process of deep frying. This review aims to provide an overview of previous studies examining the physical, chemical, and nutritional changes that occur in fried foods, the mechanisms of fat uptake during frying, and the health implications associated with the consumption of these foods. This increasing rate in consumption has been linked to various adverse health conditions. There has been a significant research focus on reducing the fat content in deep fried foods, particularly investigating the process of fat uptake during deep-fat frying. It is crucial to increase consumer awareness regarding the potential problems arising from excessive intake of deep-fat fried foods. Furthermore, further studies are needed to meet the rising demand for deep-fat fried foods while minimizing the impact on health and preserving their desirable taste.
Graphical abstract
... The UFA content of frying oil also has a significant positive correlation with the oil content of fried products (p < 0.05), which may explain the result that the UFA content of frying oil is positively correlated with the formation of HCAs. Sabally et al. and Bouchon et al. once pointed out that oil absorbed during frying was prone to build up on the surface of fried food, which was the main part of the formation of HCAs [51,52]. Tai et al. studied the effects of no frying oil and the use of lard, SBO, and coconut oil on the HCA content in fried fish patties and found that the total HCA content was at its lowest when no frying oil was used [21]. ...
Oil oxidation products can react with food substrates to produce harmful substances, and oil saturation is closely related to oil oxidation in the process of frying. Therefore, the influence of the composition of fatty acids in oil on the formation of harmful substances in fried pork balls was explored. The five frying oils with the lowest unsaturated fatty acid (UFA) content, ranked in ascending order, were palm oil, peanut oil, soybean oil, corn oil, and colza oil (64.94%, 79.94%, 82.65%, 83.07%, and 92.26%, respectively). The overall levels of four harmful substances (acrylamide, polycyclic aromatic hydrocarbons, heterocyclic amines, and trans fatty acids) found in the oil used to fry pork balls followed a descending order: canola oil, corn oil, peanut oil, soybean oil, and palm oil (33.66 μg/kg, 27.17 μg/kg, 23.45 μg/kg, 18.67 μg/kg, and 13.19 μg/kg, respectively). This order was generally consistent with the trend in the content of UFAs. Therefore, the formation of harmful substances is closely related to the saturation of oil. Compared with other frying oils, soybean oil as a household oil produces relatively low amounts of harmful substances and has less negative impact on the quality (oil content, moisture content, and higher protein digestibility) of fried products.
... A strategy for fat reduction without any additives is pre-heating prior to DF. Pre-heating creates a crust on the food surface, which acts as a physical barrier (Bouchon, 2009;Oladejo et al., 2018;Ziaiifar et al., 2008). This physical barrier minimizes permeability resulting in reduction of moisture loss (i.e., evaporation) and subsequent reduction of oil absorption. ...
... Potato frying in hot oil is one of the most complex food preparation processes, since it involves unsteady heat and mass transfer phenomena in porous media (a porous structure develops gradually in potato crust with frying), phase change of water to vapor, growth and detachment of vapor bubbles on the food surface, natural heat convection in the oil bulk combined with forced heat convection induced by the violent bubble departure from the food surface (Bouchon, 2009;Mallikarjunan et al., 2009;Sahin & Sumnu, 2009). ...
Dietary nutrition and uptake of earth-like foods are extremely important aspects for the health and performance of astronauts, especially during future planned long-term space missions. Despite the major progress in studying and designing systems for crop cultivation in microgravity conditions in the last years, there hasn’t been equal interest in food preparation processes and cooking. There are several reasons for this but it is chiefly because at present astronauts stay in space for a few months at most, so there is no serious nutritional or psychological need for earth-like food habits. This, however, will change drastically in long-term missions, e.g., to Moon and Mars. French fries are a very popular food commodity across many cultural backgrounds on earth and as such they may be appreciated by long-term space travelers of different origin. The process of frying in hot oil is associated with complex heat and mass transfer along with the growth and detachment of water vapor bubbles. These phenomena are strongly affected by buoyancy and gravitational acceleration making the study of frying at space conditions a challenging task. The present work examines potato frying in hot oil during the short duration low gravity conditions achieved in a Parabolic Flight Campaign organized by the European Space Agency. An innovative device has been constructed, allowing the simultaneous observation of bubbles dynamics above the potato surface and the thermal behavior inside the potato flesh. It is seen that even in the absence of buoyancy i.e., during parabolas, vapor bubbles still detach and depart from the surface of potato permitting hot oil to maintain contact with the potato surface and leading eventually to a fried product. Instantaneous overpressure inside potato pores due to vapor formation upon boiling of potato water is suggested as the mechanism generating the force for bubbles detachment and departure. Moreover, the amount of produced vapor is comparable among the examined values of gravitational acceleration, including the low gravity conditions during parabolas. All in all, the results of the present study provide primary experimental evidence that frying can occur in space.
... It should be noted that the nature of the fatty acids constitutes an important factor on the oxidizability of an oil. The richer an oil is in unsaturated fatty acids, the more sensitive it becomes to oxidation (Varela et al., 1988;Bouchon, 2009). ...
The objective of this study was to analyze the nutritional, mineral and fatty acid composition of a little known and underutilized aquatic plant available locally in the department of Brazzaville, Congo. The analytical methods used for the physicochemical analysis of L. schlechteri were those of the AOAC. The determination of minerals was performed by atomic absorption spectrometry. The gas chromatographic method was used to highlight the fatty acid profile. The results obtained revealed the contents of water, carbohydrates, ash, proteins and lipids respectively 97.5±1.69%, 45.45±1.64%, 13.50±1.24%, 10.7±0.65 % and finally 7.5±0.40%. Regarding the mineral content, the elements identified were calcium (1160 mg) followed by Iron (400 mg), Magnesium (360 mg) and Phosphorus (300 mg). The values of the oil indices gave respectively 1.2± 0.05 mg KOH/g oil for the acid index, 1.55± 0.1 meqO2 /kg oil for the peroxide index, 94.5±1 mg KOH/g oil for the saponification index and 93.3± 0.9% mg KOH/g for the ester index. The fatty acid composition revealed that the saturated fatty acid C16 is in the majority with 43.11% followed by C18with C18:26 at 28.68%, C18:33 at 23.24%, C18:19 at 2.78% and finally C18:0 at 2.2% in the following order C16>C186>C183>C189>C18. K e y w o r d s Evaluation, Quality, Nutrients, L. schlechteri, green vegetable
... A series of physical and chemical changes such as starch gelatinization, protein denaturation, caramelization reaction, Maillard reaction, and oil uptake could occur during the frying process, which could finally give the food a golden color, a loose and porous structure, a crisp texture, and a unique fried flavor that is accepted by consumers (Dehghannya & Ngadi, 2021;Zaghi et al., 2019). The frying conditions (time and temperature) are significant factors impacting the oil absorption in the finished product (Bouchon, 2009). The frying temperature varies from 130 to 160 • C, and the frying time is less than 2 min, according to the width and weight of the noodle (Hou, 2020). ...
Fried instant noodles have become a popular instant food in recent years, favored by consumers for their unique flavor and taste. Unfortunately, the oil content of instant noodles is generally high, so the rise of fat‐related diseases poses a major health issue. From the perspective of the cost of instant noodle manufacturers and the health of consumers, it is of great significance to reduce the oil content of instant noodles. The aim of this review article is to provide an overview of the main factors, such as raw materials and production processes, affecting oil content in instant noodles in order to suggest specific strategies to reduce the oil content in the end product. From the literature reviewed, adding acetylated potato starch/carboxymethyl cellulose, hydroxypropyl methylcellulose, or preharvest‐dropped apple powder in the noodle formulation could be a better choice to reduce oil uptake by 5%–20%. Instant noodles with lower oil content can be produced using novel alternative frying technologies, including microwave and vacuum frying. The proper management of the production processes and the implementation of enhancement strategies may result in a reduction of oil content in the end product.
... Fried foods are widely popular because of their crunchy crust, characteristic smell and taste, and golden-brown colour resulting from the Maillard reaction (Bouchon 2009). Potato croquettes (PC) and fish fingers (FF) are some of the most popular foods prepared by deep frying, during which foods are immersed into a thick layer of oil pre-heated to 150-200 °C (Khaled et al. 2015). ...
The stability of three frying oils (rapeseed, sunflower, and rice) and their effect on the nutritional value of deep-fried fish fingers (FF) and potato croquettes (PC) was evaluated, considering the nutritional importance of reducing the amount of oil absorbed by fried foods. Ten frying cycles were performed for each food to mimic the repeated frying conditions. Dry matter content of fried foods was determined gravimetrically; fat extraction was performed using a Soxhlet apparatus. Oil stability changes were evaluated using the Schaal test; colour changes were monitored spectrophotometrically. Repeated frying had no significant effect (P > 0.05) on the fat content of the tested foods but influenced the dry matter content of PC. The highest and lowest oxidative stabilities during repeated frying were observed for rice and sunflower oil, respectively. During the frying of FF, all oils tended to darken after each frying, which was not observed for PC. The intake of fat owing to the consumption of one portion of the fried FF (150 g) or PC (200 g) approximately equals 9 g and 5 g, respectively. This demonstrates that fried foods themselves (not only the oil soaked) could be a considerable source of fat.
... This corroborated with the findings of Romuli, Abass and Müller (2016) that drying can cause significant structural changes in cassava grits. Meanwhile, Bouchon (2009) reported that most pretreatment given to products are not meant to reduce moisture content but to cause microstructural alterations that will then lead to changes in the behaviour of the product. Also, there were significant differences ( p < 0.05) in hardness (N), cohe- siveness (mm), chewiness (N) and colour change of the optimized and reference sample with the latter having higher values for colour change ( Table 5 ). ...
... This corroborated with the findings of Romuli, Abass and Müller (2016) that drying can cause significant structural changes in cassava grits. Meanwhile, Bouchon (2009) reported that most pretreatment given to products are not meant to reduce moisture content but to cause microstructural alterations that will then lead to changes in the behaviour of the product. Also, there were significant differences ( p < 0.05) in hardness (N), cohe- siveness (mm), chewiness (N) and colour change of the optimized and reference sample with the latter having higher values for colour change ( Table 5 ). ...
A Box-Behnken (three-factor) response surface design was utilized to determine effect of grits rehydration level (35-45%), frying temperature (155-175 °C) and frying time (7-13 min) on some attributes (moisture, oil, textural parameters and colour) of instant Akara iwe, a cassava based fried snack and optimize the process. Sensory evaluation of the optimized sample to measure its degree of acceptability was conducted including comparison with Akara iwe from raw cassava mash. Frying temperature, frying time and grits rehydration level had significant (p<0.05) effect on moisture content, cohesiveness, springiness and colour change of instant Akara iwe. Based on desirability (71%) index, the optimal process variables for instant Akara iwe were 38% grits rehydration level at 169 °C for 9 min. The oil content of the optimized Akara iwe samples differ significantly (p<0.05) from the reference sample with the former retaining less oil. Similarly, optimized instant akara iwe had higher hardness (789.23 N) and chewiness (382.2 N) values than the reference samples and were significantly (p<0.05) different. Panelists preferred the optimized samples in terms of colour, oiliness and aroma.
... The oil content of the control sample was significantly (p < 0.05) lower than that of the other samples, probably due to the deep-fat frying process. As phospholipids are easier to absorb oil due to its low interfacial tension in the frying process (Bouchon, 2009). Moreover, alanine and glucose treatment could form a hard porous shell structure on the sample surface, which facilitated oil storage in the pores (Dana & Saguy, 2006). ...
Deep-fat fried battered and breaded foods are worldwide popular foods. In this study, egg yolk phospholipids, as well as alanine and glucose were used to generate the key odorants of fried coatings. The volatile compounds of fried coatings were extracted and analyzed by HS-SPME-GC-MS, and aroma profiles were analyzed via quantitative descriptive analysis. The results showed that the characteristic deep-fat frying odorants derived from Maillard reaction and lipids, such as methional, 2-methylbutanal and 3-methylbutanal, 2-ethyl-3,5-dimethylpyrazine, 2,4-decadienals, etc. were the highest amounts in the phospholipids & alanine and glucose treated sample, whereas the lowest in the control sample. Meanwhile, the aroma attributes had the same tendency as those of the odorants. The results proved that egg yolk phospholipids combined with alanine and glucose could be used to generate the key odorants of fried battered and breaded foods and enrich the volatile profile with a variety of Maillard reaction odorants. This treatment has a great potential use in catering industry.
... In fact, the differences between the oil contents of the fried samples were consistent with the moisture decrements of the samples. The amount of oil absorption in fried foods is associated with the amount of discarded moisture rather than the initial moisture content of the product owing to the fact that oil enters the spaces left empty by the water removal (Bouchon, 2009). We found that the oil content was higher in fried eggplant samples with lower moisture content as compared to zucchini samples. ...
Pulsed electric field (PEF) was used as a pre-treatment to investigate the oil intake and color of zucchini and eggplant slices after frying. Samples were PEF-treated at 1.0 kV/cm of electric field strength, and 1.0 kJ/kg (PEF1) and 3.0 kJ/kg (PEF3) of specific energy inputs. Frying was performed at 180 °C for 2 min. PEF3 treatment of zucchini reduced the oil content (> 32%) significantly compared to control samples whereas statistically same oil contents were obtained for eggplant. No significant differences were observed for the moisture contents of PEF-treated and untreated zucchini samples. On the other hand, moisture change was noticeable for the eggplant. Higher browning index values were calculated for PEF-treated vegetables, but this seemed to be highly dependent on specific energy inputs. Results revealed that PEF processing can be used before deep frying to reduce the oil content of zucchini with the formation of desired brown color.
... In today's society with all its modern trappings, repeated frying with vegetable oils is a widely used procedure for meal preparation [1,2]. During deep fat frying, oil is heated at a temperature above 150 0 C for a long time in the presence of air. ...
The process of repeated frying of dietary vegetable oils plays a significant role in the generation of free radicals, which could be determined on the level of performance, lipid peroxidation and antioxidant defense system respectively. This study was conducted to investigate the possible toxicological effects of repeated frying on the levels of -carotene, -tocopherol and malondialydehyde of some commercially edible vegetable oils. Ten different samples of vegetable oils were thermally stressed through repeated frying for three consecutive days. The results indicated that the amount of malondialdehyde formation was highest in the rancid palm oil sample (from 0.166 mmol/ml in day 0 to 0.212 mmol/ml in day 3), while fresh palm oil sample had the lowest amount of malondialdehyde formation (from 0.025 mmol/ml in day 0 to 0.041 mmol/ml in day 3). The refined deodorized palm olein, groundnut oil, congealed and locally made vegetable oil samples also showed a significant increase (P < 0.05) in the concentration of malondialdehyde with repeated frying of oils. The significant increase (P < 0.05) in the levels of MDA was marked by a significant decrease (P < 0.05) in their -carotene and -tocopherol levels during the course of repeated frying of the oils.
... Furthermore, it is also a more convenient source of high-energy foods, as well as a fast and convenient way of food preparation Freire et al. (2013). Deep-fat frying temperatures can be as low as 130°C to the minimum while 170-190 °C is the most common frying temperature for foods Bouchon (2009) during this process a set of chemical reactions takes place including hydrolysis, polymerization, and oxidation which leads to degradation of the quality of frying medium and involves heat and mass transfer and complex interactions between the material with the frying medium Vitrac et al. (2002). Chapli Kebab or Kabab is a traditional Pashtun-style minced kebab, which is normally made from ground meat mostly of beef but can also contain meat from other sources like mutton or chicken with a mix of different kind of spices, chapli kabab is made in shape of a patty. ...
... The holes and fractures in the fried shrimp produced by EFF were less, and the final structure was more compact. This kind of structure is not conducive to the absorption and retention of oil, thereby leading to a lower final oil content [116]. ...
Frying is commonly used by consumers, restaurants, and industries around the globe to cook and process foods. Compared to other food processing methods, frying has several potential advantages, including reduced processing times and the creation of foods with desirable sensory attributes. Frying is often used to prepare starchy foods. After ingestion, the starch and fat in these foods are hydrolyzed by enzymes in the human digestive tract, thereby providing an important source of energy (glucose and fatty acids) for the human body. Conversely, overconsumption of fried starchy foods can promote overweight, obesity, and other chronic diseases. Moreover, frying can generate toxic reaction products that can damage people's health. Consequently, there is interest in developing alternative frying technologies that reduce the levels of nutritionally undesirable components in fried foods, such as vacuum, microwave, air, and radiant frying methods. In this review, we focus on the principles and applications of these innovative frying technologies, and highlight their potential advantages and shortcomings. Further development of these technologies should lead to the creation of healthier fried foods that can help combat the rise in diet-related chronic diseases.
... Research by Ajo [19] reported that the application of an edible coating with xanthan gum reduced oil absorption by up to 57% and improved the overall quality of the product, including taste, flavor, and crunchiness. One of the alternatives for processing cassava is cooking it with boiling water and then frying it by immersion in oil and coating it with edible films [20] based on proteins, such as whey, isolated soybean, some carbohydrates, pectins, and hydrocolloids that have oil barrier properties [21]. ...
The objective of this research was to study the effect of edible coatings on the physicochemical properties of cassava chips. The oil and moisture absorption in fried cassava chips that were not coated and in chips that were coated with pectin and whey protein films were determined using a completely randomized experiment design with a 33 factorial arrangement. The multifactorial ANOVA analysis of variance showed that all factors had significant statistical differences for moisture loss and oil absorption (p < 0.05). The coating type, the control, and the whey protein-coated chips presented a 321% greater oil content on average at 180 °C and 180 s than the pectin-coated chips. The density, heat capacity, and thermal diffusivity had statistical differences at all temperatures (p < 0.05). The sensory analysis showed that the coating type affected all sensory parameters, except crispness, as indicated by significant statistical differences (p < 0.05). The temperature only influenced the color of the control chips, with statistical differences (p < 0.05) at all temperatures.
... Deep-frying is a common cooking method used to fry wide array of foods where flavour, texture and appearance of food products are enhanced. Different approaches can be employed to decrease the amount of oil uptake in fried foods which includes the use of pre-frying methods (coating, osmotic dehydration, air drying and blanching), modification of frying techniques and application of post-frying techniques (super-heated steam drying) (Bouchon, 2009;Oke et al., 2017). The use of hydrocolloids in the form of edible coating or batter ingredient in fried foods to reduce oil uptake (Albert and Mittal, 2002;Kurek et al., 2017;Varela and Fiszman, 2011) is considered more feasible for commercialisation purpose compared to the use of expensive equipment (Lumanlan et al., 2019). ...
Purpose
Deep-fried banana ( Musa spp.) fritters is one of the frequently consumed fruit based snacks in Southeast Asian countries despite its substantial amount of oil content. Consistent with the demand for low fat food with maintained palatability, this study aimed to determine the quality of banana fritters as affected by batter system containing selected hydrocolloids such as pectin (PCN), whey protein isolate (WPI) and soy protein isolate (SPI).
Design/methodology/approach
Banana fritter batters were prepared with individual addition of 2% PCN (w/w), 10% WPI (w/w), 10% SPI (w/w), combination of 2% PCN and 10% WPI, combination of 2% PCN and 10% SPI and control (without hydrocolloid addition). Batter viscosity (Pa.s) and batter pick-up (%) were determined. Banana fritters were analysed for moisture and fat contents, moisture loss, colour, hardness and sensory characteristics.
Findings
Hydrocolloid addition in the batter system resulted in a higher batter pick-up and viscosity in comparison to control batter system. Moisture loss from banana fritters with batter formulation of 2% PCN and 10% SPI was the lowest while the reduction in oil content (55%) was the highest. Banana fritters with inclusion of hydrocolloids in the batter formulation were equally accepted as the control sample by the sensory panelists with a score range between 6 and 7 for most of the sensory attributes evaluated except for oiliness.
Originality/value
Application of PCN and SPI in batter system to develop banana fritters with low oil content, moist fruit core and crunchy crust is reported for the first time. Batter premix containing PCN and SPI can be produced for fresh and frozen fritters preparation.
... Meanwhile, waste vegetable oil is used cooking oil produced copiously worldwide by residences, restaurants, hotels, and other food processing facilities. In Malaysia, for example, approximately 432,000 t of waste vegetable oil was generated in 2016 based on the assumption that 20% (Bouchon 2009) of the total amount of vegetable oil consumed in that particular year, i.e., 540,000 t (Azmi 2016), was absorbed by food during cooking and frying. Although PFAD, PKFAD, and waste vegetable oil have been used in the animal feed, soap, oleochemical, nutraceutical, cosmetic, and biodiesel industries (Nandi et al. 2005;Top AGM 2010;Malvade and Satpute 2013), there are still plenty of these waste materials available that can be utilized in many other lucrative ways. ...
Water pollution and depletion of natural resources have motivated the utilization of green organic solvents in solvent extraction (SX) and liquid membrane (LM) for sustainable wastewater treatment and resource recovery. SX is an old and established separation method, while LM, which combines both the solute removal and recovery processes of SX in a single unit, is a revolutionary separation technology. The organic solvents used for solute removal in SX and LM can be categorized into sole conventional, mixed conventional-green, and sole green organic solvents, whereas the stripping agents used for solute recovery include acids, bases, metal salts, and water. This review revealed that the performance of greener organic solvents (mixed conventional-green and sole green organic solvents) was on par with the sole conventional organic solvents. However, some green organic solvents may threaten food security, while others could be pricey. The distinctive extraction theories of various sole green organic solvents (free fatty acid-rich oils, triglyceride-rich oils, and deep eutectic solvents) affect their application suitability for a specific type of wastewater. Organic liquid wastes are among the optimal green organic solvents for SX and LM in consideration of their triple environmental, economic, and performance benefits.
... On the other hand, fat content of the mango doughnuts fried with the gas fryer (DMMgf, DMRgf) were slightly higher than these values. Other findings show that the oil absorbed in fried products increases with the quantity of water lost during frying (Rossell, 2001;Bouchon, 2009;Thanatuksorn et al., 2010;Galoburda et al., 2013). The endosmosis of oil is due to filling the spaces left by the evaporated water. ...
The processing of mangoes (Mangifera indica L.) in Burkina Faso is limited by the quality, the diversification of derived products and the lack of data on the biochemical and technological characteristics of the mango varieties used. This work has been carried out with the aim of contributing to an appropriate and profitable valuation, to the improvement and diversification of the products derived from the mango. An inventory of mango processing has been carried out at 40 processing units. The physicochemical and biochemical characteristics of 20 varieties collected in the varietal collection field of mangoes have been determined. Investigation data revealed that processing units are composed of 41 % artisanal units and 56 % semi-industrial units. The main mango varieties used are Amélie, Brooks, Kent, Lippens and Springfield. The most popular technologies are mainly mango drying and process for making mango juice/nectars. Data also revealed that 95 % of the units were informed to the standards regulating mango processing. The results of the characterization of the 20 varieties of mango shown that Lippens and Julie varieties have the lowest values of weight, however they have different L*, a*, b*, colorimetric parameters. The highest levels of pulp (81.31±1.67 %) and TSS (23.1±0.00 %) are found in the Kent variety. The Amélie variety has the highest titratable
acidity levels (1.56±0.01 %), β-carotene (1752.72±41.64 μg/100 g fresh pulp) and vitamin C (58.94±1.77 mg/100 g of pulp). The Sensation variety has the highest levels of phenolic
compounds (110.41±3.11 mg GAE /100 fresh pulps). With regard to titratable acidity, pH and TSS/TA ratios obtained, the 20 varieties can be classified into very acidic groups (Amélie, Brooks, Dixon, Kent, Valencia and Sakabi), moderately acidic (Alphonso, Berverly, Galzier, Sensation, Smith, Palmer and VSB) and sweet (Francis, Irwin, Julie, Keitt, Lippens, Miamilate and Springfield). Results of the sensory tests performed on the mango doughnuts produced shown that these doughnuts were favorably appreciated by whole panel of tasters. The results of the physicochemical analyzes shown that the level of fat is higher in mango doughnuts obtained with the gas fryer than those obtained with the crepe maker that These results also shown a high loss of β-carotene contents of deep-fried doughnuts compared to those fried usingnthe crepe maker. The microbiological and physicochemical parameters evaluated during the conservation monitoring of the candied mangoes remained stable during the 6 months of observation. The present study on these 20 mango varieties is an approach aimed at providing a quality profile and a potential technological and nutritional use of these mangoes.
Key-words: Mangifera indica, mango, varieties, color, technological characteristics, nutrition,
processing, Burkina Faso
... Other fried foods fried cheese stick, popcorn, and fried tofu Frying food is one of the most common and preferred cooking methods in the Philippines, probably because it is a convenient food preparation and fried food has a savory flavor favored by Filipinos [14,15]. During the frying process, the amount of oil absorbed into foods can reach up to 40% of the total weight of the food product [16,17]. Furthermore, during frying, the heated oil undergoes deterioration due to various chemical reactions like thermal oxidation, and thermally-oxidized oil induced oxidative stress [18]. ...
Background/objectives:
Few epidemiological studies examined the association between fried food intake and hypertension. This study examined whether fried food intake was associated with higher prevalence of prehypertension and hypertension combined in a cross-sectional study of the Filipino Women's Diet and Health Study (FiLWHEL).
Subjects/methods:
This study included a total of 428 women aged 20-57 years who have ever been married to Korean men. Prehypertension was defined as 120 - < 140 mmHg of SBP or 80 - < 90 mmHg of DBP and hypertension as SBP ≥ 140 mmHg or DBP ≥ 90 mmHg. Fried food intake was assessed using one-day 24-hour recall. Fried foods were categorized into total, deep/shallow and pan/stir fried foods. The odds ratio (OR)s and 95% confidence interval (CI)s were calculated using multivariate logistic regression.
Results:
The prevalence of prehypertension and hypertension combined was 41.36% in this population. High fried food intake was associated with high prevalence of prehypertension and hypertension combined. The odds of having prehypertension and hypertension was higher in the 3rd tertile of fried food intake among fried food consumers compared to non-fried food consumers (OR = 2.46, 95% CI = 1.24, 4.87; P for trend = 0.004). Separate analysis for types of frying showed that deep and shallow fried food intake was associated with prevalence of prehypertension and hypertension combined for comparing the 3rd tertile vs. non-fried food consumers (OR = 2.93; 95% CI = 1.57-5.47; P for trend = < 0.001).
Conclusions:
This study showed the evidence that high fried food intake was significantly associated with high prevalence of prehypertension and hypertension combined among Filipino women married to Korean men.
... This leads to a number of chemical reactions in the oil, such as oxidation, hydrolysis and polymerization. These chemical reactions can alter the quality of the oil, leading to the production of various types of oxidative products [6]. Hydroperoxides and aldehydes are the primary products formed in the early stages of oxidation and absorbed by fried foods [7]. ...
The purpose of this article is to compare the quality of three edible oils de-ri ved from palm oil in Daloa’s city. The methodological approach of the ar-ticle includes, on the one hand, a field survey determining the most used oils and the number of frying carried out by the attieké-fish sellers. On the other hand, the physico-chemical parameters (refractive index, iodine index, sapo-nification index, acid index and peroxide index) of these oils were deter-mined. As a result, the most used oils are A, B and C and are heated at least 3 times by the attieké-fish sellers. After repeated heating, the values of the pe-roxide, saponification, refraction, iodine indices of oils A and B do not match those of the codex with the exception of the acid value. For oil C, only the ac-id and iodine indices correspond to the codex standards. Overall, the results of the study clearly show that the repeated heating of these oils has an influ-ence on the different physico-chemical properties studied.
(14) (PDF) Determination of Physico-Chemical Indices of Frying Oils Used by Attieké-Fish Sellers in Daloa (Mid-West of Côte d’Ivoire). Available from: https://www.researchgate.net/publication/338627160_Determination_of_Physico-Chemical_Indices_of_Frying_Oils_Used_by_Attieke-Fish_Sellers_in_Daloa_Mid-West_of_Cote_d'Ivoire [accessed Jun 16 2020].
... The frying is one of the methods of more widespread and thermal essential food processing anywhere in the world 12 . It can be defined as a particular type of baking by immersion in oil or fat food to a temperature superior to the boiling point of the water 13 . ...
The objective of the present study was to compare the compositional analyze of three types of tubers, like traditional potatoes (Solanum tuberosum) and two of them that come from untraditional like Malanga (Xanthosoma saggitifolium) and papa china (Colocasia esculenta), crops that in Ecuador aren’t used for the snacks making. The evaluated components in the primordial matter and finished material were: protein content, grease, ashes, humidity, fiber, and carbohydrates, all of them were evaluated by official methods of analyze. The experiment was realized three times for each prove. It was used a program SPSS version 23, applying a variance followed by a Tukey test (p<0,05) with the objective of determinate some meaning statistics for deviation of tubers ways of Malanga that has a significant content of protein and carbohydrates and energetic adds were higher in comparison of the traditional snacks, these results are an alternative for the consumer and the development of new products for the food industries.
... The frying is one of the methods of more widespread and thermal essential food processing anywhere in the world 12 . It can be defined as a particular type of baking by immersion in oil or fat food to a temperature superior to the boiling point of the water 13 . ...
The objective of the present study was to compare the compositional analyze of three types of tubers, like traditional potatoes (Solanum tuberosum) and two of them that come from untraditional like Malanga (Xanthosoma saggitifolium) and papa china (Colocasia esculenta), crops that in Ecuador aren’t used for the snacks making. The evaluated components in the primordial matter and finished material were: protein content, grease, ashes, humidity, fiber, and carbohydrates, all of them were evaluated by official methods of analyze. The experiment was realized three times for each prove. It was used a program SPSS version 23, applying a variance followed by a Tukey test (p<0,05) with the objective of determinate some meaning statistics for deviation of tubers ways of Malanga that has a significant content of protein and carbohydrates and energetic adds were higher in comparison of the traditional snacks, these results are an alternative for the consumer and the development of new products for the food industries.
... It has been shown previously that a decrease in moisture is directly proportional to the concentration of the enzyme added and length of incubation [6]. Furthermore, the high temperatures used in frying cause evaporation of water on the food surface, and absorption of oil by food products is known to replace existing water content [31]. ...
... During this stage, surface characteristics of the food item and oil viscosity are very key in determining oil uptake. In the surface-active mechanism, it was opined that during the frying process, chemical reactions such as polymerization, hydrolysis and oxidation occur which result in the formation of volatile and non-volatile compounds which could cause a reduction in surface tension resulting in higher oil uptake (Bouchon, 2009;Dueik, Moreno, & Bouchon, 2012). Similarly, water content and pressure development are other two significant factors that have been reported to influence oil absorption during frying (Lalam et al., 2013). ...
... Frying at some very high temperatures is the main basis of preparation of most of the processed and fried foods. During such deep frying (150 0 C-190 0 C or more), the hot oil acts as the heat transfer medium and contributes to the texture and flavor of the fried foods (Bouchon 2009). During this process, the edible oils or fats undergo various chemical reactions (Goyal and Sundararaj 2009). ...
Trans-fats are mainly created by us during conversion of liquid unsaturated fats (oils) to semisolid saturated fats to use them in the processed and fried foods. High temperature boiling and repeated boiling of oils are another two reasons for creation of these toxic fats. Trans-fats have very strong relation with development of various cardiovascular diseases, type 2 diabetes, infertility and pre-eclampsia of pregnant ladies, retarded fetal development, cancers, obesity, various allergy related diseases, neurological problems, liver dysfunction etc. Various aspects of development, use, toxicity and ways to stay outside of the effects of this toxic fat are discussed in the article comparing with other fats - different mono and poly unsaturated fats as well as saturated fats. A list of all commonly used oils along with their detail composition is added for their logical selection for use.
Aiming to understand the nutritional impact of Moringa oleifera oil (MOO) on the quality of fried potatoes as consumed, a frying study using intermittent frying at 180 °C was conducted over 5 days, with a total heating time of 15 h, against olive (OO) and sunflower (SFO) oils. Additionally, due to MOO’s higher costs, a SFO/MOO blend (80/20 w/w) was tested. With similar fat incorporation and moisture contents, potato lipid composition revealed the impact of oil oxidation over the frying time, gradually decreasing the content of unsaturated fatty acids and antioxidants, including vitamin E, carotenoids and ascorbic acid, and increasing the incorporation of trans fatty acids (TFAs) and volatile aldehydes. When the potatoes fried at the ninth hour of heating are compared, MOO and OO were still able to protect potato ascorbic acid better than SFO, due to the low oxidative stress imposed by their fatty-acid composition. SFO, on the contrary, with linoleic acid as the main fatty acid, and despite its higher content of vitamin E, demonstrated higher oxidative stress and increased incorporation of alkenals and alkadienals. Acrylamide content was generally low, as were the trans fatty acids formed and incorporated with frying time, with MOO fried potatoes having lower amounts of all these process contaminants. Interestingly, the blend SFO/MOO (80/20 w/w) doubled the amount of vitamin E in fried potatoes when compared with SFO alone, increased the ascorbic acid protection and reduced by half the amounts of volatile aldehydes, indicative of an efficient reduction of the oxidative status of the SFO-fried potatoes, with benefits to the consumer from a health point of view.
The impact of heat on food processing is important for improving the sensory and nutritional characteristics of foods while also increasing the shelf life by decreasing enzymatic and biochemical degradation reactions and removing water from the food structure. In addition to the positive features of heat application, it should also be considered that it requires high operating costs. The high-temperature food processing methods reviewed in this chapter include cooking, baking, roasting, frying, and thawing, which are unit operations in which heat is applied to foods to increase the shelf life or to improve the eating quality. In this chapter, first, the theoretical basis of the food processing operations is described. Then, processing parameters and the influence of the unit operations on the physicochemical and nutritional properties of foods are indicated. The methods and equipment used to apply these theoretical principles into practice are described in detail, and new technologies providing energy savings, lower labor costs, and improving product quality are discussed in the following sections.
Pressure evolution and material deformation during frying and post-frying of foods affect transport processes and food's textural attributes. Pressure and volume measurements have received limited attention in the frying literature. In this study, the changes in moisture content, oil uptake, temperature, pressure, and volume were measured as a function of frying time for potato cylinders. The volume change immediately after frying and after the cylinders had cooled was measured using a modified liquid displacement method. Fried cylinders continued to shrink post-frying. During frying, pressure and temperature showed similar increasing trends followed by plateauing of the temperature and a drop in pressure in the core. The measured gauge pressure remained positive throughout frying (t=300s) and up to 100s after frying. The measured gauge pressure dropped to negative values for the remaining cooling period. The temperature decreased during cooling, which is expected to have led to water vapor collapse and a drop in gas pressure. A high capillary pressure is expected to have developed in the food matrix due to water loss, causing the effective gauge pressure to become negative. The negative gauge pressure is expected to drive oil uptake and shrinkage of the food matrix post-frying.
Acrylamide is a potential carcinogen produced at higher temperatures while frying, roasting and baking. Starch‐rich foods like potatoes are known to produce acrylamide in increasing concentrations than other kinds of foods. This study focuses on mitigation of acrylamide in sweet potato, taro and cassava samples subjected to various heat‐treatment processes like oil frying, air frying and baking. Dipping of tuber slices in solutions of garlic, green tea, sodium chloride, yeast, distilled water, whey and blanching prior to frying the tubers were found to be effective pre‐treatment methods. However, the effect of the treatments depended on the sample and mode of processing. Yeast was found to produce a significant reduction in the acrylamide production in taro (98.64%) and garlic pretreatment reduced acrylamide in deep fat fried cassava samples up to 95.62%. Similarly, air fried taro samples dipped in distilled water was found to significantly reduce the browning reaction up to 96.51%; primarily due to the fact that distilled water was found to block the reaction between precursors like asparagine and reducing sugars, thereby preventing the formation of acrylamide. Influence of reducing sugar on the formation of acrylamide, when fried at different temperatures was analyzed using Response Surface Methodology (RSM), clearly indicating that the amount of reducing sugars decreased at higher temperatures with increase in acrylamide content. The attempts in the study clearly shows that simple and cost effective pretreatments can be successful applied to produce healthy tuber products with reduced concentration of acrylamide.
Background: Deep-fat fried foods are widely popular due to their distinct organoleptic and sensory characteristics. Deep-fat frying allows physical and chemical structural changes at the macro and micro levels. One of the greatest concerns regarding fried foods is their high oil content, and the excessive consumption of these foods has been linked to a range of metabolic diseases, including heart ailments, obesity, high cholesterol, and high blood pressure.
Scope and approach: This review paper presents a comprehensive and up-to-date review of various innovative frying processes, such as vacuum frying (VF), microwave frying, microwave-assisted vacuum frying (MVF), ultrasound combined microwave vacuum frying (UMVF), air frying, and radiant frying. Additionally, it explains the oil uptake mechanism, oil quality, and the effects of different pretreatments and post-frying treatments on the frying process.
Key findings and conclusions: Innovative frying processes are considered promising and capable of producing healthier fried foods compared to traditional frying; they reduce oil uptake without deteriorating organoleptic and sensory characteristics. Specifically, vacuum-assisted frying technologies, such as VF, MVF, and UMVF have significantly reduced oil uptake and acrylamide production while preserving oil quality. In addition, appropriate pretreatment and post-frying techniques play an essential role in reducing oil uptake and optimizing the frying process by saving energy.
During deep-frying, a plethora of volatile products is emitted with the fumes. These compounds could act as oil quality indicators and change the indoor air composition leading to health risks for occupants. The presented experiments focus on deep-frying of different tubers in rapeseed oil at different frying temperatures. Here, two scenarios for real-time monitoring of volatile organic compounds (VOCs) using proton transfer reaction mass spectrometry (PTR-MS) were proposed. The first, targeted, involved the application of gas chromatography with a flame ionization detector (GC-FID). The second, omics-inspired, involved the use of solid-phase microextraction (SPME) along with gas chromatography-mass spectrometry (GC-MS) and molecular networking algorithm as a complementary tool to the PTR-MS analysis. In a targeted approach, it was shown that the emission profile of pentanal and hexanal depends on the frying temperature and as the temperature increases, a sudden release of these compounds can be observed in the first minutes of frying. Meanwhile, using an omics-inspired protocol enables finding the relation between 1,4-heptadienal and 2-heptanone, octanal and limonene emissions. Using both approaches it was possible to record real-time changes in emission profiles of various oils’ degradation products. It was also observed that the emission profiles of VOCs are strictly related to the frying temperature and the type of fried tuber.
Frying is a unit operation in which food is heated in oil to alter its eating quality. A secondary purpose is to destroy contaminating microorganisms and, for some foods, to extend their shelf life. The chapter first reviews the principles of heat and mass transfer in frying and the uptake of oil by foods. There follows a description of equipment used for contact (or shallow) frying and deep-fat frying and methods to reduce energy consumption and environmental pollution. The criteria for selection of frying oils are described, together with the effects of frying on oil quality. Finally, there is a description of methods to reduce the fat content of fried foods, the effect of frying on the sensory characteristics of foods, changes to nutritional value and health concerns over fried foods.
The current study focuses on comparing the physico-chemical changes during frying of palm oil designer lipid (PODL) and two different blends of palm oil with medium chain triglycerides (MCT) over 48 frying cycles. The PV of PODL, F1 and F2 increased from 1.29 ± 0.02, 1.34 ± 0.00, 1.38 ± 0.01 to 1.36 ± 0.02, 1.83 ± 0.02, 1.94 ± 0.02 meq O2 / kg respectively after 48 frying cycles. Similarly, p-AV and Totox values were 39.5 ± 0.01 and 42.22 ± 0.01, 52.8 ± 0.02 and 56.46 ± 0.03, 61.7 ± 0.01 and 65.58 ± 0.02 for PODL, F1 and F2 respectively after 48 frying cycles confirming that PODL showed higher thermo-oxidative stability in comparison with palm oil blends. The viscosity of all the frying medium increased and also there was a change in color of frying oil upon successive frying indicating accumulation of oxidative bi-products in the frying oil. Heat transfer coefficient was also elucidated to decrease with an increase in the frying cycle for all the blends and PODL. Overall, it was clearly demonstrated that the physicochemical properties and heat transfer quality of PODL was less affected as compared with palm oil blends demonstrating excellent potential of the PODL/interesterified fat as an alternative frying medium.
Eating fried foods (deep fried) is not a healthy choice; still billions of people eat fried food because of tasty, satisfaction, craveability and broad appeal. Sub-baric deep-fat frying process conditions maintain unique characteristics of fried foods while minimizing detrimental effects. It is an alternative for processing of nutritious, healthy, palatable, and novel snack fried products. Important feature of sub-baric deep-fat frying process are protection of oil quality during frying, reduction of toxic compounds and oil uptake in the frying process. Good frying practices are quite helpful, in the routine frying conditions to achieve the better efficiency and quality of fried food.
The effect of sunflower oil treated with varying proportions of rosemary and thyme essential oils (0.3%, 0.6%, 0.9%, and 1.2%) on the lipid quality of Mediterranean horse mackerel and anchovy during traditional pan-frying was assessed in this research. Concentrations of rosemary and thyme essential oils greater than 0.9% applied to sunflower oil tend to reduce the lipid content of horse mackerel, while anchovies fried in sunflower oil with only a few concentrations of rosemary essential oil seemed to avoid a rise in lipid content that leads to frying. The addition of thyme and rosemary essential oils with the different percentages in frying oil significantly caused a reduction in the peroxide and thiobarbituric acid values of all fish samples after pan-frying (p < 0.05). However, the free fatty acid contents of all fried fish samples did not change significantly by the addition of EOs to sunflower oil (p > 0.05). According to our results, the amount of EPA and DHA in Mediterranean horse mackerel during traditional pan-frying was affected by the type of essential oils and their concentration in sunflower oil. Using EOs at different concentrations, on the other hand, has no noticeable impact on the retention of highly unsaturated fatty acids in anchovies. It shows that all of the essential oils used significantly reduce lipid oxidation and protect against EPA and DHA reduction as a result of frying in Mediterranean horse mackerel.
Machine learning algorithms were applied to predict the oil uptake of rice flour in batter-coated fried foods, depending on its physicochemical features before frying (amylose content, pasting parameters, batter viscosity). Low coefficients of Pearson correlation (0.29–0.61) were observed between the oil uptake of rice frying batters and other physicochemical parameters. Based on an exhaustive search method by the regsubsets function, the four experimental features (amylose content, peak time, peak temperature, and final viscosity) were selected as the best subset to affect the oil uptake of rice batters after frying, and then subjected to two machine learning algorithms – multivariable linear regression and multilayer perceptron neural network. Based on K-fold cross-validation, the experimental results were divided into 5 datasets consisting of each 80% training and 20% testing dataset. Compared to the multivariable linear regression (R² = 0.6204–0.7219), the iterative application of the multilayer perceptron model made a relatively higher prediction (R² = 0.7388–0.7781) of the oil uptake of rice flour frying batter. Thus, the multilayer perception model with a hidden layer outperformed the multivariable linear regression by showing higher R² and lower relative error.
Hot air frying is one of the newest processing methods that can make healthier fried foods. The mechanism of frying using this method is not understood entirely yet. There is no model available to describe the oil absorption for air-fried foods. In this research, an agent-based model was extended to describe the oil penetration procedure and study the different effects of the cellular structure of crust on oil distribution during hot air frying. Netlogo software was used for the model simulation. The simulation results of oil penetration were in good agreement with experimental data. Obtained results show that the oil penetration procedure divided into three main steps named latent phase, acceleration phase, and deceleration phase. The acceleration phase is the most critical step in doughnut oil absorption. Simulated data also show that oil penetration starts from the thinner parts of the crust. Therefore, it seems that the structure of the crust has an important effect on oil absorption pattern.
Production of high-quality fried foods with low oil content receives considerable attention from consumers and producers. The effects of electric field frying (EFF) and conventional frying (CF) on the physicochemical properties of frying oil, the oil absorption behavior, and the microstructural changes in fried shrimps were compared and evaluated in this study. Results showed the application of EFF could delay the degradation of frying oil evidently compared with CF. The increasing rate of total polar compound content, acid values, viscosity, and color deepening of EFF oil was slower (p < 0.05) than that of CF oil during the prolonged frying. The analysis of the results of low field nuclear magnetic resonance (LF-NMR) measurements confirmed our findings. In addition, the fried shrimps produced by EFF had reduced oil content (p < 0.05), increased water retention (p < 0.05), even oil distribution, and decreased microstructure damage via the observation of magnetic resonance imaging, confocal laser scanning microscope (CLSM), and scanning electron microscope. Results may provide ideas for producing high-quality fried products with low oil content and delaying oil degradation during frying.
Defatted rice bran (DRB) is a by-product in the rice bran oil industry generated in large quantities. Unfortunately, DRB, is underutilized and often discarded despite containing valuable proteins, minerals, dietary fiber, and bioactive phytochemicals. This study examined the effects of four DRB substitution levels (0, 10, 15 and 20% of mixed flour in batter and pre-dust) on fried chicken nugget properties. Increasing DRB substitutions increased both batter viscosity and pickup (%) resulting in thicker nugget crusts. The 15 and 20% DRB substitutions significantly decreased both the crispness and lightness of battered fried chicken nuggets. Furthermore, oil content decreased significantly while moisture and fiber content increased in DRB batter-coated chicken nuggets compared to the control without DRB. In conclusion, 15% or less DRB substitution in batter reduces fried chicken nugget oil content while maintaining product quality and healthfulness.
This paper is concerned with the industrial frying process and in particular the role of the frying oil and the influence this has on the food. Attention is drawn to various factors that can adversely affect the quality of the frying oil. In this paper the term «frying oil» is used. Other publications may refere to frying fat or frying shortening. As these are all used well above their melting points, and are fully liquid, the term oil is preferred by the present author, there being no quality difference between the products so named. The quality of oil or fat used for frying is of paramount importance with regard to the quality of the fried food. The amount of oil absorbed in different fried foods varies; battered fish or chicken absorb about 15% frying oil, while breaded fish or chicken absorb up to 20% frying oil. The amount of oil absorbed by doughnuts varies from 15-20% of their final weight. This is, of course, in addition to the shortening used in preparation of the dough, giving a final oil/fat content of up to 30%. Standard or traditional potato crisps absorb the highest quantity of oil, and up to 35 or 40% of the final food may be frying oil. Recently, modern technology has been introduced to produce low-fat crisps, but these still have about 20% absorbed oil. It should therefore be remembered that the fat used for frying becomes part of the food we eat. The most important aspect of industrial frying is therefore the frying oil, and in surveying factors that affect frying oil quality, this paper reviews (a) oil properties and composition; b) transport, packaging and storage of oil; c) the nature of the food fried and its interaction with the frying oil; d) the frying equipment and the process of frying; and e) the evaluation of the quality of the frying oil during use. Each of these factors is important in its own way, and it is of no advantage to concentrate on one or two, or even three, of these aspects without appreciating that there may be additional influences on the quality of the frying oil, and thus the fried food.
The convective heat transfer coefficient is a useful parameter in characterizing heat flow across a fluid/solid interface when the fluid flow field is complex and solution of the coupled transport equations impractical. While convective heat transfer coefficient values for many unit operations have been tabulated, the boiling phase of immersion frying has not been quantified. The objective of this study was to develop a laboratory method for the measurement of the convective heat transfer coefficient during immersion frying. The method that was developed was applied to the immersion frying of potato cylinders at an oil temperature of 180C. The convective heat transfer coefficient was initially 300 W/m2K, it increased sharply to 1100 W/m2K, and gradually decreased to 300 W/m2K over the duration of the process. Use of this new method will allow the study of the effects of oil temperature, oil quality, product shape/size, and product quality on heat transfer coefficients.
To understand the influence of frying oil's physical properties on heat transfer, heat transfer coefficient and oil viscosity were measured for combinations of oil type, temperature, and condition. the lumped capacity method for heat transfer in a high thermally conductive metal gave convective heat transfer coefficients. A capillary viscometer in a convective air heater provided viscosity data at frying temperatures. Frying time and oil temperature significantly affected viscosity. Oil viscosities were not statistically different between fresh and 12 h frying oil or 12 and 24 h frying oil, while between the remaining frying times the oil viscosities were statistically different. Corn oil viscosity showed the greatest increase over 36 h and the highest correlation between viscosity and heat transfer coefficient (−0.959).
Fried products contribute to a significant amount of the overall oil consumed in the western world's diet. Fat intake has been identified as one of the most important factors contributing to several health risks. The desire to consume more nutritious and healthier foods has created significant pressure on the industry to reduce fat of fried products. Yet, lipids have still not been matched in their unique functionality and universal appeal. To address these risks, concentrated research efforts have focused on reducing fat absorption during the frying process. The objective of this review is to summarise the data available, and to focus on the mechanisms and factors affecting oil uptake during deep-fat frying. A holistic approach integrating the complexity of the process and its mechanisms is adopted, highlighting some of the possible factors that play a significant role in oil absorption. Some of the multiplicity interrelationships among three domains: oil, product and process are discussed. The main conclusions highlight the fact that oil uptake mechanism is an extremely complex process, still not completely understood. Additional studies focusing on the microstructure changes occurring in the product during deep-fat frying are recommended in order to further elucidate the various mechanisms affecting oil uptake, and to provide the means and the tools required to control the various processes that govern the phenomena.
The convective heat transfer coefficient is a useful parameter in characterizing heat flow across a fluid/solid interface when the fluid flow field is complex and solution of the coupled transport equations impractical. While convective heat transfer coefficient values for many unit operations have been tabulated, the boiling phase of immersion frying has not been quantified. The objective of this study was to develop a laboratory method for the measurement of the convective heat transfer coefficient during immersion frying. The method that was developed was applied to the immersion frying of potato cylinders at an oil temperature of 180 C. The convective heat transfer coefficient was initially 300 W/m2K over the duration of the process. Use of this new method will allow the study of the effects of oil temperature, oil quality, product shape/size, and product quality on heat transfer coefficients.
Fat distribution in deep fat fried French fries can be visualized directly by carrying out the frying process in oil supplemented with 1-3% Sudan Red B and by subsequent microscopic inspection of cross-sections of the fried potato sticks. Sudan Red B is an oil-soluble azo dye which is commonly used in microscopy and is still heat-stable at temperatures of 150-180 °C. Migration of the dye into the potato stick is absolutely identical to that of the frying oil. Frying experiments at 180 °C for 1-10 min showed that the frying oil remains virtually on the surface and in the first few layers of cells. No further penetration towards the centre of the potato sticks was observed. The staining method could be useful for other fried potato products and also for fried bakery and meat products.
Modeling Immersion Frying as a Moving Boundary Problem
Abstract
A quantitative description of the heat and mass transfer which occurs during the
frying of foods is needed to aid in product and process development. The goal of this
research was to develop a predictive mathematical model of the heat and mass transfer in
the product during immersion frying. The model, developed using macroscopic balances,
was comprised of four non-linear, coupled, partial differential equations and associated
initial and boundary conditions. The method of Crank-Nicholson was used to reduce the
problem to a set of nonlinear, algebraic equations; Gauss-Seidel iteration was used to
solve these equations.
It was found that the model was able to predict temperature profiles, moisture
content, and crust thickness in close agreement with experimentally determined data.
Heat transfer in the crust and core regions was primarily by conduction. The conversion
of liquid water to vapor at the crust/core interface served to fix the interface temperature
at the boiling point. Mass transfer in the core was modeled using diffusion theory.
Magnetic resonance images of un-fried and fried potato samples showed that oil resides
solely in the outer crust layer of the fried material.
The validated model was used for a sensitivity analysis. The effect of changing
the physical and thermal properties required by the model on temperature profiles,
moisture content, and crust thickness was studied. Temperature profiles in the crust
region were primarily a function of oil temperature. Core region temperature profiles
were not affected by oil temperature due to the presence of a 100°C boundary
temperature at the crust/core interface. Heating rates of the core region were affected by
thermal conductivity and specific heat of the core. Values chosen for diffusivity of the
water/starch system had a strong effect on the final moisture content of the fried sample.
It was found that crust thickness was affected by thermal conductivity of the crust region,
oil temperature, moisture content, and thermal conductivity of the core region. As oil
temperature and thermal conductivity of the crust increased so did crust thickness. As
moisture content and core thermal conductivity decreased crust thickness increased.
The mathematical models that describe the immersion-frying period and the post-frying cooling period of an infinite slab or an infinite cylinder were solved and tested. Results were successfully compared with those found in the literature or obtained experimentally, and were discussed in terms of the hypotheses and simplifications made. The models were used as the basis of a sensitivity analysis. Simulations showed that a decrease in slab thickness and core heat capacity resulted in faster crust development. On the other hand, an increase in oil temperature and boiling heat transfer coefficient between the oil and the surface of the food accelerated crust formation. The model for oil absorption during cooling was analysed using the tested post-frying cooling equation to determine the moment in which a positive pressure driving force, allowing oil suction within the pore, originated. It was found that as crust layer thickness, pore radius and ambient temperature decreased so did the time needed to start the absorption. On the other hand, as the effective convective heat transfer coefficient between the air and the surface of the slab increased the required cooling time decreased. In addition, it was found that the time needed to allow oil absorption during cooling was extremely sensitive to pore radius, indicating the importance of an accurate pore size determination in future studies.
Several studies have highlighted the importance of the cooling period in oil absorption in deep-fat fried products. Specifically, it has been established that the largest proportion of oil which ends up into the food, is sucked into the porous crust region after the fried product is removed from the oil bath, stressing the importance of this time interval. The main objective of this paper was to develop a predictive mechanistic model that can be used to understand the principles behind post-frying cooling oil absorption kinetics, which can also help identifying the key parameters that affect the final oil intake by the fried product. The model was developed for two different geometries, an infinite slab and an infinite cylinder, and was divided into two main sub-models, one describing the immersion frying period itself and the other describing the post-frying cooling period. The immersion frying period was described by a transient moving-front model that considered the movement of the crust/core interface, whereas post-frying cooling oil absorption was considered to be a pressure driven flow mediated by capillary forces. A key element in the model was the hypothesis that oil suction would only begin once a positive pressure driving force had developed. The mechanistic model was based on measurable physical and thermal properties, and process parameters with no need of empirical data fitting, and can be used to study oil absorption in any deep-fat fried product that satisfies the assumptions made.
Potato tubers of cv. Record UK were used to produce crisps (chips) of different slice thickness (40–70 thousandths of an inch; 1-1·75 mm approximately) using an industrial slicer. The slices were examined to determine maxumum thickness variability of each slice and the range of values produced at each set thickness. Prepared crisps were analysed to determine the effect of slice thickness on the yield and composition of crisps. A series of regression equations were produced relating slice thickness and total surface area of slices to yield, moisture content and oil content of product. Oil uptake during frying was found to be related to the surface area of the potato slices.
The convective heat transfer coefficient during deep-fat frying of potatoes was determined at different temperatures. The temperature, 0.1 cm below the top and bottom surfaces of a 0.05×0.05×0.005 m potato sample was monitored over time. The thermal conductivity and specific heat of the sample were expressed as a function of time, and the data were analyzed using the heat transfer equation with an explicit finite difference method. Crust formation occurred primarily at the bottom surface of the potato slice. Therefore, the frying was examined at the bottom surface; before and after the crust formation. The convective heat transfer coefficient ranged between 300 to 335 W / m2°C for the top, and 450 to 480 W/m2°C for the bottom surface before crust formation. After crust formation, it varied between 70 to 150 W/m2°C for the bottom surface within the studied temperature range of 150 to 190 °C.
A relationship between moisture loss and oil adsorption with frying time during deep fat frying of french fries has been developed. A first order kinetic equation was used, in which the rate constant is a function of the main process variables (oil temperature, sample thickness and oil type). This model was applied to a wide range of experimental data and its parameters were estimated using non-linear regression analysis. The results showed that oil temperature and thickness of potato strips have a significant effect on oil uptake and moisture loss of french fries, while the use of hydrogenated oil in the frying medium does not affect mass transfer phenomena.
The viscoelastic behaviour of french fries during deep fat frying after two different types of drying pre-treatment (air drying and osmotic dehydration) was examined under uniaxial compression tests. The stress-strain data of the compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (σmax), the maximum strain (εmax), the elasticity parameter (E) and the viscoelastic exponent (p). The effect of air drying duration and the type of osmotic solution used on the compression behaviour of fried potatoes was introduced through the corresponding effects upon the model parameters. Pre-fry drying as well as osmotic pre-treatment increase the maximum stress and maximum strain of french fries during frying. Air drying pre-treatment increases the crispness of potato strips while osmotic pre-treatment does not affect it, with the exception of sugar solutions.
Deep-fat frying is one of the most important unit operations in both the catering and food processing industries. Although many aspects of the frying process are still poorly understood, studies of the chemistry and physics of frying in recent years have provided the means of optimizing the process. In addition to ensuring consistent, high-quality products, such optimization procedures can improve the profitability of frying operations.
The effects of pretreatment and processing conditions on the quality of vacuum fried apple chips were studied. As blanched apple slices were pretreated by immersing in fructose solution and freezing prior to vacuum frying, more uniform porosity was observed on the surface (or cross-section) of apple chips as examined by scanning electron microscopy (SEM). During vacuum frying, the moisture content and breaking force of apple chips decreased with increasing frying temperature and time while the oil content increased. The L values of fried apple chips decreased apparently with increasing frying temperature. However, when apple slices were fried at 100°C for up to 20 min, both a and b values increased rapidly. Statistical analysis with the central composite rotatable design showed that the moisture content, oil content, color, and breaking force of apple chips were significantly (P⩽0.05) correlated with concentration of immersing sugar solution, frying temperature and frying time. Based on surface responses and contour plots, optimum conditions were: vacuum frying temperature of 100–110°C, vacuum frying time of 20–25 min, and immersing fructose concentration of 30–40%.
A multiphase porous media model has been developed to predict the moisture migration, oil uptake and energy transport in a food material such as a semi-dry potato during deep-fat frying. The model predictions are validated using experimental data from the literature. Spatial moisture profiles show two distinctive regions (dry or crust region near the surface and wet region in most of the core) with a sharp interface which can be referred to as the evaporation front. Spatial temperature profiles show two distinctive regions—higher but constant temperature gradient region near the surface, and lower temperature gradient region in the core. In the crust region, vapour diffusional flux is comparable with vapour convective flux. In the more moist core region, capillary flux of liquid water is comparable to the convective flux of liquid water. Therefore, all three modes of transport—diffusional, capillarity, and pressure driven (Darcy) flow are found to be important. Sensitivity of the final product moisture and temperature to changes in oil temperature, initial moisture content of the sample, thickness of the sample, and the surface heat and mass transfer coefficients are discussed.
Osmotic dehydration as a pretreatment before frying in order to produce low-fat french fries was examined. A relationship between frying kinetics and the type of solution used for osmotic dehydration before frying of french fries has been developed. The effect of osmotic dehydration on the structural properties (apparent density, true density, specific volume and internal porosity) and color parameters (lightness, a, b) of french fries was also investigated. Four types of solutions (sugar, NaCl, maltodextrine 12 and maltodextrine 21) were used. The results showed that osmotic pretreatment has a significant effect on oil uptake and moisture loss of french fries, as well as on the structural properties and color parameters of french fries. Osmotic dehydration pretreatment decreases oil and moisture content of french fries, while the porosity and intermit of color increased.
The mechanism of oil absorption of tortilla chips during cooling was analyzed using capillary pressure theory. The experimental and theoretical results obtained with this mechanistic model agreed well. Computer simulations were made to determine the effect of different process conditions on the final product oil content. The results show higher oil content for tortilla chips with higher initial moisture content, smaller radius, lower cooling air temperature, and higher interfacial tension.
A novel method utilizing 14C palmitic acid for image analysis and liquid scintillation for quantifying oil uptake of French fries undergoing deep-fat frying is described. Radiolabeled computerized image analysis of the fried product furnished comprehensive visual information on the distribution and localization of oil uptake which was limited to the crust. A significant high linear correlation (R2 = 0.977; P < 0.001) was found between oil uptake measured by liquid scintillation and differential scanning calorimetry, and between liquid scintillation and radiolabeled imaging (R2 = 0.861; P < 0.001). The high specificity and sensitivity of the method allows quantifying uptake of very low oil concentrations ranging from several milligrams. Oil quantification via liquid scintillation was more sensitive than image analysis and requires up to 3 order of magnitude lower concentration of the radiolabeled marker. The low concentration and inherent stability of the radiolabeled chemical make this technique uniquely suitable for studying oil uptake mechanism during deep-fat frying of foodstuffs. Keywords: Deep-fat frying; radiolabeled; liquid scintillation; image analysis; oil uptake.
4-Hydroxy-2-trans-nonenal (HNE) is a cytotoxic secondary lipid peroxidation product of linoleic acid. Previous investigations in this laboratory
showed that HNE is formed in thermally oxidized soybean oil, which is high in linoleic acid. Continuous exposure of the oil
to frying temperature (185°C) for up to 6 h graduallyincreased the formation of HNE and other polar lipophilic aldehydes.
Additional investigations in this laboratory showed that HNE is absorbed into food fried in thermally oxidized oil in the
same concentration as was found in the oil. In the present experiment, the effect of intermittent heating on the formation
of HNE in soybean oil was compared with continuous heating. Soybean oil samples were heated either for 1 h each day for five
sequential days or for 5 h continuously at 185±5°C. The thermally oxidized soybean oil samples were analyzed by HPLC for the
presence of HNE and three other polar lipophilic α-,β-unsaturated hydroxyaldehydes: 4-hydroxy-2-trans-hexanal, 4-hydroxy-2-trans-octenal, and 4-hydroxy-2-trans-decenal. Under intermittent and continuous heating over a total of 5 h, the concentration of these compounds increased similarly.
These results indicate that the formation of HNE and other hydroxyaldehydes at frying temperature is a cumulative result of
oxidation of PUFA over time.
The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose–NaCl–water, 20–5–75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.
Reports of the presence of acrylamide in a range of fried and oven-cooked foods1, 2 have caused worldwide concern because this compound has been classified as probably carcinogenic in humans3. Here we show how acrylamide can be generated from food components during heat treatment as a result of the Maillard reaction between amino acids and reducing sugars. We find that asparagine, a major amino acid in potatoes and cereals, is a crucial participant in the production of acrylamide by this pathway.
The uptake of oil during deep-fat frying of potato slices was followed by frying slices for an equal length of time, introducing a fat-soluble and heat stable dye into the oil at different times before the end of frying and measuring the fraction of dyed oil compared to the total oil content. Total oil content was measured by a refractometric method, and the content of dyed oil by a spectrophotometric method. Results from these measurements were compared to those obtained by removing slices after various periods of frying and analysing fat content. The experiments with dyed oil showed conclusively that oil does not penetrate the potato slices during frying, but is taken up by the slice only when it is removed from the frying pan due to adhesion of oil to the surface of the slice. Therefore, oil uptake is primarily a surface phenomena involving an equilibrium between adhesion and drainage of oil upon retrieval of the slice from the oil bath.
Differential scanning calorimetry (DSC) was used to determine the oil uptake of commercial frozen par-fried potatoes after frying at 180 °C in colza/soybean oil. The enthalpy and temperature range of the crystallization peak for the pure frying oil were 47.2 J/g and −44 to −50 °C, respectively. DSC was performed by cooling samples of crust and core of fried potatoes from 10 to −60 °C at 1 °C/min and the oil content calculated from the peak area. The crust contained almost 6 times as much oil as the central core (23.6% vs 4%, dry weight basis), as visualized by light microscopy. Only 87% of the oil in the intact crust can be removed by solvent extraction, the rest being extractable only after grinding. Deviation between DSC and Soxtec extraction methods was less than 3%. The DSC method is fast, specific, and reliable, does not use solvents, requires smaller samples (<100 mg) than conventional solvent extraction methods, and can also detect freezable water. Keywords: Differential scanning calorimetry; oil; frying; fried potatoes; microstructure
The oil-absorption capacity of different restructured potato chips during deep-fat frying was investigated. Low-leach potato flake was chosen as the major ingredient, whereas native and pregelatinized potato starches were studied as complementary ingredients. Results showed that oil absorption increased significantly when reducing product thickness in all products. Interestingly, it was found that the product containing native potato starch as an ingredient picked up the lowest amount of oil when sheeted into a thick chip, whereas it absorbed the largest amount of oil when sheeted into a thin chip. Those findings were mainly attributed to crust microstructure development as revealed by electron microscopy and confocal microscopy.
The effect of added powdered cellulose and methyl cellulose on oil uptake during deep-fat frying of donuts and falafel balls was determined. A new criterion, UR, expressing the oil uptake ratio between the weight of oil uptake and the weight of water removed was introduced. This criterion was valuable in assessing effectiveness of reducing oil uptake during deep-fat frying. Methocel was significantly more effective than powdered cellulose in reducing oil uptake.
The porosity of a restructured potato product ranged from 0.089 to 0.168 after fluctuating subfreezing storage temperatures. A linear relation was found between oil uptake during frying and porosity prior to frying. Bulk and particle density, and porosity were monitored for up to 5 min during deep-fat frying. Particle density increased gradually, bulk density decreased and porosity increased noticeably. After an initial short period, oil uptake correlated linearly with porosity of the fried product. A new term, “net porosity” which excluded the void volume occupied by oil was developed for describing the oil uptake mechanism.
The effect of added fructose (0–10% w/w) on restructured potato product surface characteristics, mechanical properties, moisture loss, oil uptake and color changes during deep-fat frying was investigated. The apparent fractal dimension derived from the silhouettes of the sample contour was related to surface ruggedness, and displayed a marked linear effect of the added fructose on reducing its value from 1.27 to 1.08. The apparent fractal dimension correlated linearly with oil uptake and UR, suggesting a practical criterion for predicting oil uptake during deep-fat frying. Added fructose reduced water diffusivity coefficients of pre-fried specimens from 2.00 × 10−9 to 1.26 × 10−9 m2/s. Porosity ranged from 0.79 to 0.82.
Refined soybean oils were degraded at 190°C for 60h to a total polar material of 61.54%. The effect of fresh to highly degraded oil on the physical and thermal properties of the oil as well as on the Final quality of tortilla chips was determined. Surface tension decreased significantly with oil degradation (P < 0.05). Colour readings also changed significantly with oil degradation (P < 0.05) and were more pronounced after 30h of frying. Foam and off-flavour developed between 20 and 30h of degradation suggesting that the oil should have been discarded when the total polar material reached 27%. The convective heat transfer coefficient changed more rapidly after 30h of frying. The values of the convective heat transfer coefficient correlated highly with viscosity (−0.98). The oils, whether fresh or degraded, behaved as Newtonian fluids. Viscosity was significantly affected by oil degradation time and temperature (P < 0.05). The effect of temperature on the viscosity of the oils was described by an Arrhenius equation. Viscosity changed more rapidly with temperature as the degradation time increased. Tortilla chips were fried in fresh and degraded soybean oils. Total oil content and fracturability of tortilla chips were not affected significantly by oil degradation time (P < 0.05). However, the oil content adhering to the surface of the tortilla chips was significantly higher (P < 0.05) in the tortilla chips fried in degraded oil than in fresh oil.
The heating and water loss of a single tortilla chip during deep fat frying was investigated experimentally and the data were analyzed by writing two heat and mass transfer balances. the equations were solved using explicit finite difference technique. Oil uptake as a function of frying time was described by a first order exponential equation. the empirical and theoretical heat and mass transfer agreed well.
The effect of oil temperature on the moisture loss and oil uptake as a function of frying time was analyzed. Moisture loss rate increased as temperature increased. the effects of temperature on oil uptake were not significant during the first 15 s of frying, however, the final oil content was higher for the tortilla chip fried at 190C than at 150C for 60 s.
Frying induces major structural changes in the surface of foods influencing oil uptake. This work discusses the use of several different methods of microscopy as well as techniques of image analysis to study frying at the microstructural level. Hot-stage video microscopy was instrumental in assessing geometrical changes in cells of potato tissue and in starch in real time. The swelling of starches inside cells appeared to be retarded compared with that in starch suspensions. Confocal laser scanning microscopy (CLSM) permitted ‘optical’ sectioning of the crust, revealing that oil was located in the interior in pockets or surrounding intact cells. The manipulation of microscopy data by image processing is also presented.
Length-scale and area-scale analyses, two of the scale-sensitive fractal analyses performed by the software Surfraxhttp://www.surfract.com, were used to study food surfaces measured with a scanning laser microscope (SLM). The SLM measures surfaces, or textures (i.e., acquires topographical data as a collection of heights as a function of position), at a spatial and vertical resolution of 25 μm. The measured textures are analyzed by using linear and areal tiling (length-scale and area-scale analysis) and by conventional statistical analyses. Area-scale and length-scale fractal complexities (Lsfc and Asfc) and the smooth-rough crossover (SRC) are derived from the scale-sensitive fractal analyses. Both measures proved adequate to quantify and differentiate surfaces of foods (e.g., chocolate and a slice of bread), which were smooth or porous to the naked eye. Surfaces generated after frying of potato products (e.g., potato chips and French fries) had similar values of Asfc and SRC, and larger (implying more complex and rougher surfaces) than those of the raw potato. Variability of surface texture characterization parameters as a function of the size of the measured region was used in selecting the size of the measured regions for further analysis. The length-scale method of profile analysis (also called the Richardson or compass method) was useful in determining the directionality or lay of the anisotropic texture on food surfaces.
The objective of this study was to determine the thermal conductivity, specific heat, density (true and bulk), and the texture characteristics of tortilla chips and to study the effects of moisture content, oil content, and frying time on these properties. Tortilla chips were fried in fresh soybean oil for different times at 190C. Results showed that the values of thermal conductivity of tortilla chips decreased from 0.23 to 0.09 W/mC, specific heat from 3.36 to 2.31 kJ/kgC, and bulk density from 880 to 579 kg/m3 as frying time increased. In general, the crispness of tortilla chips increased as frying time increased.
Deep-fat frying is a rapid and low cost process widely used to prepare tasty food. During this cooking process, oil is used both as the heating medium and as an ingredient producing calorific products. Nutrition has become a major health issue, especially in developed countries where increasing obesity is a problem, particularly among children. Many food research projects involving snack food industries therefore attempt to understand oil uptake during the frying process in order to control and reduce the fat content of fried products without deteriorating their desirable organoleptic characteristics. The main objectives of this paper are to review the literature on the frying process and more precisely the mechanisms and parameters involved in the oil uptake phenomenon. Both products and processes will be considered and their influence via experimental results will be discussed.
During the last decade much attention has been given to investigating oil absorption during frying. Several studies have suggested the key role of the dehydrated crust, which is thought to control the main mechanisms in oil absorption, that is drainage and capillary suction during post-frying cooling. To contribute to a better understanding of these mechanisms, we have used infrared microspectroscopy at the Synchrotron Radiation Source at Daresbury (UK) to monitor the oil distribution in fried potato cylinders. We report what we believe to be the first quantitative data on oil distribution within a fried product. Results show that the oil distribution within the crust reflects the anisotropic nature of the porous region in accordance with the proposed mechanism of oil absorption.
Fundamental theory of surface chemistry was utilized to develop an equation for calculating initial interfacial tension between a product and liquid. The relationship provides a practical approach to overcome the complexity of quantitatively determining interfacial tension of foods. The range of interfacial tension between a restructured potato product and the frying medium was 0.01 to 5.23–10−3 N/m. This range was determined using various frying media or additives. A power relationship was found between the initial interfacial tension and uptake of oil or other frying media. A model of capillary rise in porous media was implemented to explain the linear relationship between uptake and contact angle.
Microwave, hot air (40 and 105°C) and freeze drying were used to remove varying amounts of moisture from 1.3 mm thick potato slices. The partially dried slices were then fried in oil at 165°C either for a constant 2 min or a variable frying time based on the amount of pre-drying. The microwave and hot air treatments resulted in a reduction in the final oil content, which was related to the degree of pre-fry drying. Freeze drying resulted in an increase in the oil content, again related to the initial moisture reduction. Oil distribution at the microscopic and macroscopic level was determined and found to be related to the initial moisture distribution in the slice. It is suggested that pre-fry drying may be a more successful point of influence than post-fry treatment in the manufacture of a‘lower fat crisp’.
The variations in moisture content and oil content of samples of 1.5-mm thick slices of potato (c.v. Record U.K.) were examined after various frying times at frying temperatures of 145, 165 and 185°C. The loss of moisture and the uptake of oil were found to be interrelated and both were linear functions of the square root of frying time. Within the temperature range examined, moisture loss and oil uptake were found to be independent of frying temperature. From the data and visual observations the mechanism of moisture loss and its influence on oil content in the final product were discussed. Suggestions are made for means of reducing the total oil content by modifications in the frying process.
The purpose of the present investigation was to study the influence of the degree of degradation of different kinds of oils used as a frying medium on fat uptake and texture of frozen pre-fried French fries. As has been found, the degradation degree of the frying medium depends on the kind of oil and processing time. Liquid hydrogenated rapeseed oil exhibited the best thermo-oxidative stability among the oils under investigation. The kind of oil influenced fat uptake and the texture of French fries. The lowest fat uptake was observed with French fries fried in solid oil. Some correlations between fat uptake and changes in fatty acid content were found in the frying medium during frying. Fat absorption increased with increasing unsaturated fatty acids and decreasing saturated fatty acid content. The texture of French fries fried in hydrogenated oils was harder than that exhibited by French fries fried in liquid rapeseed oil. The hardness of French fries fried in liquid oils decreased during frying while the hardness of French fries fried in solid oil increased. Some correlations between the texture of French fries and iodine value and fatty acids content of frying media were found. The hardness of French fries increased with increasing content of saturated fatty acids and decreasing unsaturated fatty acids and trans isomer fatty acid content. Copyright © 2005 Society of Chemical Industry
We studied the use of edible films to reduce fat absorption in fried foods. A mathematical model was developed incorporating heat, moisture and fat transfer in the food and the film. Moisture diffusivities of the food and the film were 0.33×10−7 m2/s and 0.25×10−7m2/s, respectively. Fat diffusivities were 0.103×10−8m2/s for the food and 0.604×10−9m2/s for the film. Thermal diffusivities were 0.102×10−6m2/s for the food and 0.156×10−6m2/s for the film. Film diffusivities were determined for gellan gum films at a thickness of 2.0 mm during frying.