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Internal temperature of strawberries during freeze-drying at different plate temperatures (m 30, e 40, f 50, t 60, oe 70 C). The dotted line ( O O O O O O O O )
Source publication
Drying kinetic, as well as color and volume variation, of whole and sliced strawberries were investigated after freeze-drying under various temperatures (30, 40, 50, 60 and 70°C). Dehydration time increased proportionally to the thickness of the product and heating plate temperature markedly reduced it. Freeze-drying caused a pronunciation in red c...
Context in source publication
Context 1
... glass transition temperature of freeze- dried strawberries was found to be 38 C (36). The internal temperature of strawberries during freeze-drying at different heating plate tempera- tures is shown in Figure 6 together with the glass transition temperature of freeze-dried strawberry. If the heating plate temperature is higher Figure 5. Percentage of collapsed strawberries during freeze-drying at dif- ferent plate temperatures (oe detected by volume reduction, e detected by visual observation). ...
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Citations
... Berries being very susceptible to skin rupture during air-drying may cause severe fruit bleeding during drying. The freeze-drying process, however, is known for producing lowshrinkage berry products [57]. Different letters indicate significant differences between the different drying treatments, while the asterisk (*) indicates significant differences between samples with and without pretreatment. ...
The impact of cryogenic pretreatments on drying performance was studied in blueberries, seabuckthorn fruits and green grapes. The fruits were immersed in liquid nitrogen in 2 min freezing/thawing cycles (one to five). Untreated samples were used as the control. Drying experiments were carried out on treated and non-treated berries at 50 °C and 1 m/s (hot-air-drying), 50 °C and 25″ Hg vacuum (vacuum-drying), 30 mTorr total pressure and 25 °C shelf temperature (freeze-drying). The weight loss evolution of the foodstuffs was measured as a function of time. Microscopic (SEM and optical) determinations of the epicarp were performed. A visual inspection was performed and color changes and volume reductions were assessed before and after dehydration. The thickness of the berries’ epicarp decreased between 20 and 50% (depending on the fruit) after 3–5 immersions in liquid N2. The drying kinetics was accelerated significantly for the three tested drying processes (i.e., drying time decreased from 48 to 16 h for blueberry freeze-drying). The best quality of dried berries was observed for pretreated blueberries after freeze-drying, keeping their volume, shape and color after the process. This work shows that “tailor-made” dried berry products with desired properties can be achieved and drying performance can be improved by the application of ultra-low temperature pretreatments.
... A standard freeze-drying processing condition was fixed at 0.3 mbar (30 Pa) with a condenser temperature of −85 • C and a shelf temperature of 50 • C. This shelf temperature was chosen by considering quality optimization studies on freeze-dried strawberries from the related literature [2,26,27]. The freeze-dryer system includes dedicated software (SCADA Software V1 LPC Plus Martin Chris, Osterode am Harz, Germany) to set, control, and monitor the freeze-drying process under the selected processing conditions. ...
... The tone angle parameter hue and chroma [27] were obtained according to Equations (3) and (4), respectively. ...
... The values were obtained from the data in Figure 4. Table 2 presents the mean, lower, and upper values of primary drying times, taken from the data set, the regression lines, and the respective upper and lower 95% CI lines. These FD times, between 20.5 and 27.1 h, are comparable to the times obtained in [27]: 30 h for whole strawberries freeze-dried at 27 • C or 24 h for those at 50 • C. However, much more information would be required (i.e., on the size of the fruits, the heat and mass transfer surface, and the total volume of fruits relative to the void volume of the FD chamber, among others) to conduct an exact comparison. ...
Freeze-drying (FD) processing preserves foods by combining the most effective traditional technologies. FD conserves the structure, shape, freshness, nutritional/bioactive value, color, and aroma at levels similar to or better than those of refrigerated and frozen foods while delivering the shelf-stable convenience of canned/hot-air-dehydrated foods. The mass transfer rate is the essential factor that can slow down the FD process, resulting in an excessive primary drying time and high energy consumption. The objective of this study was to reduce the FD processing time using CO2 laser technology to improve product competitiveness in the preservation of whole strawberries. The research process consisted of the selection and characterization of fresh strawberries, followed by preparation, pre-treatment, freeze-drying, a primary drying time assessment, and a quality comparison. Experiments were carried out using strawberries without micro-perforation and with five and eight micro-perforations. Quality parameters were determined for fresh, frozen/thawed, and freeze-dried/rehydrated strawberries. It was found that the primary drying time can be significantly reduced by 20% (95% CI) from 26.7 h for non-perforated fruits to 22.3 h when five micro-perforations are made on each strawberry. The quality parameters used to evaluate the strawberries did not show significant differences when comparing frozen/thawed fruits with freeze-dried/rehydrated fruits. The experiments conducted in this study showed that freeze-drying may efficiently compete with freezing technology when processing whole strawberries.
... Various drying techniques are used to prevent the fruit spoilage and extend shelf life. Freeze-drying is one of the best methods for removing water from biological products compared to other dehydration techniques [6]. Freeze-drying (FD) produces the highest quality food product, but it is the most expensive process for producing dehydrated products due to high energy consumption [7]. ...
In order to preserve the nutritional properties of fruits after dehydration, it is necessary to use appropriate storage methods. The traditional freeze-dried and combination-dried i. e. vacuum pre-and freeze post-dried, freeze pre-and vacuum post-dried, mid-infrared-freeze-dried, and freeze-mid-infrared dried blueberry samples were stored in vacuum packs for 6 months. The reference drying method, i.e. freeze drying at a pressure of 80-90 Pa and a temperature range between −25 and 20°C, with a drying time of 22 h, was used. The blueberries were mid-infrared dried at 60°C for 5 min before and after freeze-drying, and the experimental materials were also vacuum dried at 60°C for 4 h at 7 kPa vacuum pressure before and after freeze-drying. Drying operation times were ranked from the shortest to the longest as follows: freeze-mid-infrared drying, mid-infrared freeze-drying, freeze pre-and vacuum post-drying, and vacuum pre-and freeze post-drying and conventional lyophilization. The aim of this study was to investigate the effects of different storage conditions, namely refrigeration (5°C in a refrigerator) and room temperature (23°C on a shelf in a dark place) on the moisture content, water activity, firmness, rehydration ratio, polyphenol-and flavonoid content, as well as antioxidant capacity of dried blueberries. The dried and vacuum-packaged blueberries stored in the refrigerator and at room temperature can be characterized by the stability of their physical and chemical properties throughout the storage period. It was found that a traditional freeze-drying (FD), freeze-drying and vacuum-drying combination of 4 h at 60°C (FD-VD4h60°C) together with vacuum packaging at ambient temperature, is sufficient to ensure a shelf-stable whole blueberry product.
... However, it also has some downsides, such as high energy costs and prolonged processing times (Prosapio & Norton, 2017). Despite these drawbacks, freeze-dried strawberries maintain high food quality and extended shelf life (Shishehgarha et al., 2002). ...
... Many studies on freeze-dried strawberries have been conducted in the literature. Some of them are Shishehgarha et al. (2002) investigated the drying kinetics as well as color and volume changes after freezedrying whole and sliced strawberries at different temperatures (30, 40, 50, 60, and 70 C). They found that after freeze-drying the strawberries, there was a volume reduction of 8% in whole strawberries and 2% in sliced strawberries. ...
This study aims to investigate the effects of different drying temperature profiles on freeze‐dried strawberries. The drying temperature profiles used in the trials were as follows: Trial I: 20°C–6 h, 30°C–6 h, 40°C–6 h, 50°C–3 h, Trial II: 30°C–6 h, 40°C–9 h, 50°C–6 h, Trial III: 50°C–6 h, 40°C–9 h, 30°C–6 h. The quality of the freeze‐dried strawberries was assessed by measuring various parameters, including shrinkage, total dry matter, color, water activity, and anthocyanin content. The shrinkage rate was resulted at least in the Trial I (3.61% height, 5.44% width). Among all trials, the highest total dry matter content was found in Trial II (95.41%). Color values of freeze‐dried strawberries, the redness value was the highest in Trial I (27.45). Trial III had the highest value of anthocyanin content (317.48 mg/100 g dry matter).
Practical applications
This study will contribute scientifically to the comparative analysis of freeze‐dried strawberries based on various freeze‐drying trials. This study will assist in determining the most suitable drying profile for freeze‐dried strawberries in terms of the desired quality, physical, and chemical properties.
... The main reason for the high production cost is that the drying process takes too long. Considering the important effects of product thickness and porosity on drying speed in the drying process, drying the whole strawberry takes quite a long time (Duan et al., 2010;Liu et al., 2017;Shishehgarha et al., 2002). Shishehgarha et al. (2002) showed that in the freeze dryer, where the plate was heated between 30 and 70 °C, drying took 48 h to reach the desired moisture content of all strawberries. ...
... Considering the important effects of product thickness and porosity on drying speed in the drying process, drying the whole strawberry takes quite a long time (Duan et al., 2010;Liu et al., 2017;Shishehgarha et al., 2002). Shishehgarha et al. (2002) showed that in the freeze dryer, where the plate was heated between 30 and 70 °C, drying took 48 h to reach the desired moisture content of all strawberries. ...
The aim of this study is to dry whole strawberries, which are a sensitive and high value-added food, with different heating rate approach in different drying stages developed to overcome the problems encountered in microwave freeze-drying (MFD). To do this, a specially designed microwave (2450 MHz) freeze-drying system developed in our laboratory was used. Internal temperatures at two different whole strawberries which are one at the center and one at the edge of the basket were recorded during drying experiments by using a signal conditioner and fiber optic probes. Drying experiments were carried out until a moisture content of below 10% by weight was attained. Heating rates determined by preliminary trials of 0.035 °C/min and 0.2 °C/min were applied to whole strawberries in the primary and secondary drying stages, respectively. The quality parameters of microwave freeze-drying and freeze-dried whole strawberries were compared. In this context, dried strawberries were subjected to some physical (moisture content, water activity, texture, and color) and chemical (vitamin C, total phenolic content, and antioxidant capacity) analyses. Microwave freeze-drying (MDF) was able to preserve the vitamin C content of all strawberries by approximately 55% while yielding a final product of substantially similar quality to freeze-drying (FD).
... The main indicator determining the quality of freeze-dried berries is the sensory evaluation of the finished product, which depends on parameters such as the shelf temperature and the duration of freeze-drying. Shelf temperature has an effect on the freeze-drying time, the higher the temperature, the less time it takes to dry, but higher temperatures can also worsen the organoleptic performance of the final product, which is consistent with the research by Shishehgarha et al. [56]. ...
Fresh berries contain numerous components that can undergo complex changes during the drying process. This study aims to investigate the effect of freeze-drying on the sensory and chemical properties of black currant and sea buckthorn berries. Freeze-drying was performed at a shelf temperature of 35–55 °C with a step of 5 °C and durations of 18, 20, 22, and 24 h. Comparing the final freeze-dried berries with their fresh counterparts, it was observed that at a shelf temperature of 50 °C and a drying time of 18 to 20 h, there was a minimal loss in the content of vitamins, organic acids, and carbohydrates. However, based on organoleptic evaluations, the best results were achieved after drying for 20 h. Furthermore, the preservation of citric and malic acids in black currant berries, along with citric, tartaric acids, and sucrose in sea buckthorn berries, was only at 45.6% when the freeze-drying time was extended to 22 h. Considering the physical and chemical properties of listed freeze-dried berries, the optimal parameters were identified as a shelf temperature of 50 °C and a drying time of 20 h. The findings from this study serve as a foundation for selecting appropriate freeze-drying parameters for various types of berries.
... Furthermore, freeze drying may result in oxidation retardation, resulting in little colour deterioration. The preservation of foods' nutraceutical components requires little colour deterioration (Shishehgarha et al., 2002). Additionally, the researchers observed that increases in redness and yellowness followed a first-order kinetic model in which vacuum, oven, and microwave-dried samples resulted in significant browning of the final products. ...
Eggplant, also known as Solanum aethiopicum (S. aethiopicum), is a highly favoured vegetable globally and belongs to the Solanaceae family. Various research studies have provided evidence of African eggplant's biological properties, such as antioxidant potential, anti-inflammatory, anti-cancer, anti-diabetic, liver-protective, and renal-protective effects. Therefore, our investigation focused on examining the impact of S. aethiopicum on the cytotoxicity of HeLa cells, which are derived from human cervical cancer. Fruits were freeze-dried or oven-dried before being subjected to aqueous infusion or hot aqueous extraction. Hot aqueous extracted (oven-dried) samples contained the highest concentration of total phenol and flavonoids. After that, HeLa cells were treated with hot aqueous extracts. After a 24-hour incubation period, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was conducted. According to the cytotoxicity analysis, neither oven-dried nor freeze-dried induced significant inhibitory effects towards HeLa cell proliferation. These findings suggest that both extracts demonstrated weak cytotoxic effects on cervical cancer cells.
... Rehydration and texture are actually two criteria that are intimately related to the final use of the freezedried product and cannot be viewed as absolute standards. Fruits that have been dehydrated are typically meant to be added to foods like corn flakes, cereal bars, ice cream, pastry sauces, etc. 2011 (Ciurzyska) Makhlouf et al. (2002), establishes that the fresh fruits with high moisture content are difficult to dehydrate using conventional drying procedures since doing so causes substantial physical damage, including collapse and serious bleeding from skin rupture. Under varied freeze-drying shelf temperatures (30 , 40 , 50 , 60 , and 70 ), under varied freeze-drying shelf temperatures (30 , 40 , 50 , 60 , and 70 ), Shishehgarha et al. (2002) studied the various quality metrics (drying kinetics, color, and volume variation) of sliced and whole strawberries. ...
... Fruits that have been dehydrated are typically meant to be added to foods like corn flakes, cereal bars, ice cream, pastry sauces, etc. 2011 (Ciurzyska) Makhlouf et al. (2002), establishes that the fresh fruits with high moisture content are difficult to dehydrate using conventional drying procedures since doing so causes substantial physical damage, including collapse and serious bleeding from skin rupture. Under varied freeze-drying shelf temperatures (30 , 40 , 50 , 60 , and 70 ), under varied freeze-drying shelf temperatures (30 , 40 , 50 , 60 , and 70 ), Shishehgarha et al. (2002) studied the various quality metrics (drying kinetics, color, and volume variation) of sliced and whole strawberries. Whole and sliced strawberries saw an average volume reduction of 8% and 2%, respectively, after freeze drying at shelf temperature. ...
... The material's composition and kind may have an impact on how much the freeze-dried product shrinks. According to Khalloufi and Ratti (2003) and studies by Shishehgarha et al. (2002) for freeze-dried whole strawberries under different temperatures in the range of from 30 to 70 , the material's shrinkage did not significantly differ under the different shelf temperatures of 20 , 40 , and 70 for apples (13%) and strawberries (8%). This investigation shown that although the quantity of collapsed fruits increased with the heating temperature, the value of fruit shrinkage remained independent of shelf temperature. ...
Freeze-drying or lyophilization is defined as a method of removing water by sublimation of ice crystals from frozen material. When compared to products dried with traditional methods, suitable parameters of process application allow the best quality products to be obtained. Freeze-drying method has been successfully applied to different food products such as meats, coffee, juices, dairy products, pumpkin, strawberries, guava, spices, tomatoes etc. Recently, the market for ‘natural’ and ‘organic’ foods is strongly growing as well as the consumer’s demand for foods with minimal processing and high quality. From this perception, the market for freeze-dried processed foods is not only increasing but also diversifying.
... Color and volume variation, and the drying kinetics of freezedried strawberries (whole and sliced) were examined by Shishehgarha et al. [49]. The authors found that FD reduced the strawberry volume by 8 % (whole) and 2 % (slices), but the extent of shrinkage was independent of the dehydration temperature. ...
The impact of various freeze‐drying (FD) methods on the drying efficiency and quality of dried fruits and vegetables is reviewed. Additionally, a brief overview of recent advances in FD methods is provided. The FD technique is characterized by the following key properties: ability to maintain original texture and color, the highest nutritional value, and appropriate rehydration rate due to the porous tissue of the product. Recently, various combination methods have been tested to improve the drying speed and save energy when FD fruits and vegetables. This includes combining FD systems with other techniques such as ultrasound, microwave, vacuum, infrared radiation, pulsed electric field (PEF), and CO2 laser perforation. Combined benefits of these technologies include increased mass transfer rates, shorter dehydration time, energy savings, improved product quality, lower shrinkage, higher rehydration capacity, and flexibility to dry and manufacture the many types of dried fruits and vegetables pieces.
... Similar research finding reported by Jangam et al. [52] revealed that freeze-dried mangoes, avocados and pineapples retained their sensory characteristics and shelf stabilities. The very low water content of freeze dried fruits helps them to have a longer shelf life [57]. However, freeze dried fruits have a high moist air absorption tendency and additional barrier to water absorption solutes such as Arabic gum, tricalcium phosphate and maltodextrin should be added to increase its shelf stability [58,59]. ...
Fruits are perishable horticultural crops grown in tropical and sub-tropical areas of the world. It is a richest source of micro nutrients and phyto chemicals that contributed a significant role in human health. Mango, avocado, papaya, guava and pine apple are popular and economically important tropical fruits due to their essential nutritional properties and appreciated eating quality. However, in developing countries, upto 50% of those fruits are lost after harvest due to improper post-harvest handling practices. Edible coating, dip in calcium chloride solution, hot water treatment and drying are easily applicable post harvest treatments used in the preservation of such tropical fruits. Shelf life of mangoes coated using edible coating material can be extended up to 18 days without rotting and developing unpleasant-flavour relative to coated guava, papaya, avocado and pine apple fruits. Dipping harvested fruits in various concentration of calcium chloride solution exhibited different storage life. Consequently, mango fruits treated with 10% of calcium chloride solution preserved for 30 days at 12°C and 85-90% relative humidity. Guava fruits treated by hot water at 45oC for 3 minute lasts upto 31 days under room temperature. In this review maximum shelf life up to 9 months was found for Avocado fruit dried using freeze drying method.
