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A study was undertaken to investigate the feasibility of heat-treating sweet onions under controlled commercial conditions. Three test runs were conducted whereby approximately 4 m3 of onions for each test were passed through a continuous-flow drier. Set-point temperatures of 43 degrees C, 43 degrees C, and 46 degrees C and durations of heat treatm...
Citations
... To ensure long term storage at room temperature, onion must undergo an important postharvest treatment called bulb curing where heat is applied to dry out the outermost scales and neck (Maw et al., 2004). The formation of these protective layers results in cell death and tissue browning. ...
A R T I C L E I N F O Keywords: senescence programmed cell death postharvest disorders storage-induced stress A B S T R A C T Postharvest performance of fresh horticultural products is largely affected by processing and storage conditions. Various practices such as chemical and physical treatments and controlled or modified atmosphere storage can delay the senescence and reduce deterioration. However, the treatments and storage environment may also be stressful and induce detrimental physiological, metabolic and molecular changes resulting in quality loss. The macroscopic symptoms of quality decline have gotten an appropriate attention, but the processes underlying the defects at the cellular level are not well understood. It is suggested that some of the postharvest disorders may involve programmed cell death (PCD): a genetically determined process of cellular suicide indispensable for normal plant development and an important mechanism for survival in response to stressful environmental factors of biotic and abiotic origin. In this review the contribution of PCD to postharvest senescence and storage-related deterioration of perishable horticultural products is discussed. For better comprehension of plant PCD, the major concepts are outlined. Senescence is considered as a specific form of PCD. Examples of recent and earlier findings demonstrating the incidence of storage-related PCD are presented. It is suggested that revealing the implication of PCD in postharvest disorders may trigger the development of new or optimized preservation strategies addressing cell death. Identification of PCD related markers can be a promising tool for predicting the shelf life of harvested products. The control over postharvest stress-induced PCD may be beneficial for the postharvest industry in sustaining the quality in the supply chain as well as in breeding programs for obtaining products with improved tolerance to storage-induced stress.
... However, this process is expensive and is efficient for only greenhouse and small area. • Heat treatment of harvested bulb with continuous flow dryer is effective for reducing post harvest diseases of onion (Maw et al., 2004). ...
Fusarium wilt is a serious problem in brinjal production. Fusarium spps. are among the most important phytopathogenic and toxigenic fungus, producing diseases in almost all commercially important plant species. Brinjal is susceptible to a variety of fungal and bacterial diseases. Fusarium wilt is a soil-borne fungus that has been reported to infect various solanaceous plants such as brinjal, potatoes, tomatoes, and peppers. This disease is a significant biotic limitation in brinjal production because Fusarium spp. penetrates the roots and proliferates in vascular tissue, interfering with the plant's water conducting vessels, making it difficult to control. Because of the soil-borne nature of this plant pathogen, its spores can survive in the soil for many years, leaving chemical fungicides ineffective. Chemical, cultural, and biological approaches are some of the most popular practices used to manage this condition. Chemical fungicides are used extensively, accumulating toxicity in the environment and causing residual issues. Microorganisms in the rhizosphere provide an excellent control for soil-borne plant diseases. For the management of Fusarium wilt disease, Trichoderma viride, Bacillus subtilis, and Pseudomonas fluorescens are recommended.
... Curing is an important postharvest treatment required to store bulbs for longer time (Maw et al., 1997a). Curing is a process intended to dry off the neck and outer scales of the bulb (Bayat et al., 2009;Maw et al., 2004). Curing is a constant process which can occur at any stage from harvest to marketing whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). ...
... Curing is a process intended to dry off the neck and outer scales of the bulb (Bayat et al., 2009;Maw et al., 2004). Curing is a constant process which can occur at any stage from harvest to marketing whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). Curing of onion is an important problem because of seasonal production and location specific, whereas the consumption of onion throughout the year and it is not location specific. ...
Aspergillus niger was found to be predominantly
associated with Aspergillus rot of pomegranate in
orchard as well as after harvest and storage but in
storage Aspergillus niger cause severe damage due
to favorable conditions. Therefore, Three fungicides,
two antifungal agent and three plant extracts were
evaluated for their efficacy against both isolate of
Aspergillus nigerin vitro and one contact fungicide
(mancozeb), two antifungal agent and three botanicals
were used in fruit dip treatment. Mancozeb at 0.5, 1.0
and 1.5 per cent inhibited the maximum mycelial
growth of both the isolates as 100 per cent at all three
concentrations followed by chlorine water that caused
100 per cent inhibition at 4 per cent and 6 percent
concentration while boric acid least effective and the
botanical extracts of neem oil and ginger (rhizome
extract) at 4 and 6 per cent concentration were
effective in vitro while garlic extract was lest effective
compare with neem oil and ginger extacts. When
evaluated by fruit dip method for injured inoculated
fruits under laboratory condition, Mancozeb at all
three concentration and chlorine water at 6%
concentration were effective in reducing fruit rot
followed by boric acid. The botanical extracts (neem
oil and ginger) were effective against A. niger in fruit
dip treatment at 4 and 6 per cent concentration,
respectively.
... An important postharvest treatment required for long-term storage of onion bulbs is curing. Curing is a drying process intended to dry down the bulb (Maw et al., 2004;Bayat et al., 2010) to prevent the loss of moisture and attack by pathogenic organisms during storage. Standard conditions for curing are blowing hot air at around 38°C with no RH control for several days (Bansal et al., 2018). ...
... Hot-air curing of bulbs is an important postharvest treatment, used to 44 dry out the outer scales, which are then transformed into a complete skin. This skin protects 45 the bulb from water loss and suppresses disease incidence, thereby maintaining higher 46 quality during storage (Chope et al., 2012;Downes et al., 2009;Maw et al., 2004). 47 Application of postharvest heat treatment, 33 °C at 98% relative humidity (RH) for a few 48 days to a few weeks, to detached outer and inner scales reveals their differential responses 49 to the heat stress (Galsurker et al., 2018). ...
Postharvest heat treatment stimulates desiccation and browning of outer scales of onion ( Allium cepa . L) bulb to dry papery skins. Inner scales resist the heat treatment, as evidenced by high moisture levels. During heating, inner scales showed increasing soluble sugar levels followed by higher osmolarity, vs. a dramatic decrease in both in the outer scales. Exogenous feeding of outer scales with sucrose, glucose or fructose solutions before heat treatment reduced water loss during heating, suggesting a role for soluble sugars in water retention and therefore, heat tolerance. Vacuolar invertase (VInv) is a key enzyme regulating the levels of sucrose, glucose and fructose in plant tissue. VInv -silencing in potato plants prevented the accumulation of reducing sugars in heated leaves, increasing water loss. In onion outer scales, VInv activity increased during heating but reducing sugars decreased, possibly due to their rapid metabolism during scale senescence to form skin. Transcriptomic analysis demonstrated upregulation of genes involved in lignin biosynthesis and secondary cell-wall formation in outer scales during heat exposure, and upregulation of genes involved in energy-related pathways in inner scales. This study reveals the dual role of soluble sugars in different onion scales, as osmoprotectants or building blocks, under heat stress.
Highlight
Hexose formation in the inner scales of onion is associated with heat tolerance, while in the outer scales, the hexoses are metabolized for onion skin formation.
... Another important postharvest treatment required for long-term storage of onion bulbs is curing (Maw et al., 1997a). Curing is a drying process intended to dry down the necks (Bayat et al., 2010) and outer scales of the bulbs (Maw et al., 2004) to prevent the loss of moisture and attack by pathogenic organisms during storage. From harvest to storage, curing can occur at any stage, whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). ...
... Curing is a drying process intended to dry down the necks (Bayat et al., 2010) and outer scales of the bulbs (Maw et al., 2004) to prevent the loss of moisture and attack by pathogenic organisms during storage. From harvest to storage, curing can occur at any stage, whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). ...
Vidalia onions (Allium cepa) are very susceptible to infection from pathogens and diseases compared with other types of onions. Botrytis neck rot (BNR) (Botrytis allii) is the most common and destructive storage disease, whereas sour skin (Pseudomonas cepacia) can cause significant bacterial losses, particularly, for late season cultivars. The objective of this study was to assess the effects of different fungicide and bactericide drenches on marketability of Vidalia onions using the cultivar Savannah Sweet grown, harvested, and graded for high-quality onions. Six different fungicide treatments were evaluated, including fludioxonil at two different rates, fluopyram and pyrimethanil in combination, and pyraclostrobin and boscalid in combination with a water-only and an untreated entry. In addition, four different bactericide treatments were evaluated, including copper hydroxide and copper sulfate pentahydrate with a water-only and untreated control. Treatments were applied by drenching the onion bags with 1 gal of solution at the desired concentration. Onions treated with fungicide were inoculated with the pathogen that causes BNR, whereas the bactericide treatments were inoculated with the pathogen that causes sour skin by placing a single inoculated bulb into each bag. Half of the bags were heat-cured for 48 hours and all of the onions were stored immediately under refrigerated conditions at 34 to 36 °F for 2 or 4 months. Bactericide treatments were not heat-cured the second year of the study. Onions were evaluated after 1 and 14 days of shelf life. For both years, all the fungicide applications were effective with more marketable onions compared with the controls. Fludioxonil, fluopyram/pyrimethanil, and boscalid/pyraclostrobin had the highest percentage of marketable onions compared with the water or untreated controls. Fluopyram/pyrimethanil and boscalid/pyraclostrobin fungicides had significantly higher percentage of marketable onions than the controls but were similar to the low rate of fludioxonil. Bactericide applications were not effective in reducing losses when compared with the controls. © 2018, American Society for Horticultural Science. All rights reserved.
... Often, artificial curing, the more costly method, is used to supplement cheaper natural curing (Boyette et al. 1992). Currently, this process is controlled simply by time and human visual inspection (Maw et al. 2004). However, varietal, seasonal and year-to-year differences can require different time periods for the curing procedure (Maw et al. 1997b). ...
The use of dielectric properties of materials for applications in agriculture is reviewed, and research findings on the use of dielectric heating of materials and on sensing of product moisture content and other quality factors are discussed. Dielectric heating applications include treatment of seed-borne pathogens, stored-product insect control, seed treatment to improve germination, soil treatment for pest control, and conditioning of products to improve nutritional value and quality maintenance. Quality sensing applications reviewed include the sensing of moisture content in grain, seed, fruit and nuts, and other quality attributes of fruits and vegetables.
... The postharvest treatment required for long-term storage of onions is curing (Maw et al., 1997a) is a drying process intended to dry out the necks (Bayat et al., 2010) and outer scales of the bulbs (Maw et al., 2004) to reduce loss of moisture and prevent decay during storage. From harvesting to storage, curing can occur at any stage, whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). ...
... The postharvest treatment required for long-term storage of onions is curing (Maw et al., 1997a) is a drying process intended to dry out the necks (Bayat et al., 2010) and outer scales of the bulbs (Maw et al., 2004) to reduce loss of moisture and prevent decay during storage. From harvesting to storage, curing can occur at any stage, whenever the conditions around the bulb become favorable to remove moisture from the bulb (Maw et al., 2004). There are two ways of curing onion bulbs: artificial and natural. ...
Vidalia onions (Allium cepa) are a branded product of southeastern Georgia marketed under a federal marketing order. They are short-day, yellow onions with a Granex shape that are susceptible to a number of diseases postharvest, limiting the amount of time they can be marketed. Postharvest treatments and storage methods can help extend their marketability. Thus, the objective of this study was to evaluate these postharvest treatments and storage conditions on quality of three Vidalia onion varieties: ‘WI-129’, ‘Sapelo Sweet’, and ‘Caramelo’. All varieties were undercut, then either harvested immediately (zero cure), field cured (2 days), or forced-air heat cured (3 days at≈37 °C) when judged mature. ‘WI-129’, ‘Sapelo Sweet’, and ‘Caramelo’ represent early, midseason, and late varieties, respectively. Bulbs were then sorted and stored in refrigerated storage [0–1 °C, 70% relative humidity (RH)], sulfur dioxide (SO2) (1000 mg•L–1 in 2010 and 5000 mg·L–1 in 2011, one time fumigation) followed by refrigeration, ozone (O3 (0.1–10 mg•L–1; continuous exposure, 0–1 °C, 70% RH), or controlled-atmosphere storage [3% oxygen (O2), 5% carbon dioxide (CO2), 0–1 °C, 70% RH]. After 2 and 4 months, bulbs were removed from storage, and evaluated after 1 and 14 days for quality and incidence of disorders. ‘Caramelo’ had the lowest percent marketable onions after curing in 2010, while ‘WI-128’ had the lowest percent marketable onions in 2011. There was a rain event immediately before harvesting ‘Caramelo’ that may have contributed to low marketability in 2010. Heat curing improved marketability for ‘Sapelo Sweet’ and ‘WI-129’ in 2010 compared with no curing. In 2011, heat curing resulted in more marketable onions for ‘Sapelo Sweet’ compared with no curing. Curing had no effect on ‘Caramelo’ in 2011 and field curing had the greatest percent marketable onions for ‘WI-129’ in 2011. In 2010, controlledatmosphere storage had more marketable onions compared with SO2 for ‘Caramelo’ and was better than simple refrigeration or O3 with ‘WI-129’. In 2011 refrigeration, controlled-atmosphere storage, and O3 were all better than SO2 with ‘Caramelo’. ‘Sapelo Sweet’ and ‘WI-129’, on the other hand in 2011, had better storage with SO2 compared with other storage methods. Onions stored for 2 months had 32% and 17% more marketable onions after removal compared with 4 months of storage regardless of storage conditions for 2010 and 2011, respectively. Poststorage shelf life was reduced by about one-third, 14 days after removal from storage regardless of the storage conditions. © 2015, American Society for Horticultural Science. All rights reserved.
... Onions with a short shelf life are used within a short time period or they are processed as a sauce, fried chips, onion powder, etc. However, heating is the best method to increase the storage potential of sweet onion cultivars with a low shelf life [8]. Dehydrated onion has great commercial value because of its culinary and medicinal properties. ...
Heating effect on total phenol, flavonoids, antioxidant activity, and sugar content of six onion varieties has been quantitatively investigated to explore the effect of different temperatures. The onion varieties comprised one red-skinned variety, two white-skinned varieties, and three yellow-skinned varieties. The heating temperature was scanned at 80°C, 100°C, 120°C, and 150°C for 30 minutes each, and quantitative analysis was performed relative to the powdered onion at ambient temperature. Quercetin, glucosides and sugar content were analyzed using high-performance liquid chromatography. The total phenolic and antioxidant content increased in all six varieties. The total flavonoid levels showed a considerable change. On heating the onion samples at 120°C for 30 minutes, the red-skinned variety showed the highest level of total phenolic content [13712.67 ± 1034.85 μg of gallic acid equivalent/g dry weight (μg GAE/g DW)] and total flavonoids [3456.00 ± 185.82 μg of quercetin equivalents/g dry weight (μg Q/g DW)], whereas the content of total phenolics and total flavonoids were 13611.83 ± 341.61 μg GAE/g DW and 3482.87 ± 117.17 μg Q/g DW, respectively, for the yellow-skinned (Sunpower) variety. Quercetin and its glucoside contents increased up to 120°C and then decreased at 150°C, whereas the sugar content continuously decreased with heating. All cultivars showed the same pattern in the heating effect, and the predominant flavonoids were destroyed at higher temperatures. Therefore, it is improper to expose onion powder to a temperature higher than 120°C.
... Oftentimes, artificial curing, the more costly method, is used to supplement cheaper natural curing (Boyette et al., 1992). Currently, this process is controlled simply by time and human visual inspection (Maw et al., 2004). However, varietal, seasonal, and potentially year-to-year differences can require different time periods for the curing procedure (Maw et al., 1997b). ...
Microwave sensing offers an opportunity to determine nondestructively the amount of moisture in materials by sensing the dielectric properties of the material. Dielectric properties of Vidalia onions grown in southeastern Georgia were measured with an open-ended coaxial-line probe and network analyzer in the range from 200 MHz to 20 GHz. Frequency dependence and moisture dependence of dielectric properties were analyzed for moisture contents between 8% and 91%. Moisture content was linearly correlated with the dielectric constant at higher frequencies for the entire moisture range. A density-independent function that incorporates both the dielectric constant and loss factor was tested across multiple frequencies and moisture ranges. Use of this function enabled prediction of moisture content with high accuracy (R2 = 0.99) up to 40% moisture content.
