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Advisor: V. R. Sagar
Other Titles: M Sc
Type: Thesis
Agrotags: sowing, yields, fruits, grain, genotypes, sowing date, summer, planting, developmental stages, crops
Abstract: The present study entitled, “Dehydration of onion: cultivar suitability and technological conditions for retaining functional quality” was conducted at the Division of Post Harvest Technology, IARI, New Delhi during 2008-2010. Two onion cultivars namely, Pusa White Round and Pusa Red were selected and stored for four months under ambient condition for storage study. To carry out the experiment the cultivars were studied for their physico-chemical constituents variation during storage and their drying behaviour. On the basis of physico-chemical constituent variations the cultivar Pusa Red was found more suitable for longer period of storage as it retain more pungency, total phenols, antioxidant activity throughout the period of storage as compared to Pusa White Round. With regard to drying behaviour, Pusa White Round was found more suitable for dehydration purpose as it retains low reducing/non reducing ratio, less browning, higher rehydration ratio and total solids/ha. To optimize the preteatments for retaining the nutritional quality of dehydrated onion slices, the peeled onion bulbs were cut into 3 mm thick slices. They were treated with different pre-treatments, namely CaCl2 1% (T1), CaCl2 2% (T2), CaCl2 1% + KMS 0.2% (T3), NaCl 2% (T4), NaCl 2%+ sulphuring (T5) along with one lot of control (T0). For successful effect of treatment the onion slices were dipped into the treated solutions for 10 min and dried at 58±2ºC in a cabinet drier for 7-8 hours upto 4-5% moisture content in the product. On the basis of nutritional quality assessment in respect of retaining higher amount of pungency, total phenols, antioxidant capacity, ascorbic acid rehydration ratio and sensory score with least moisture content and non enzymatic browning in the finished product, the treatment (T3) calcium chloride + potassium metabisulphate (CaCl2 +KMS 0.2%) was found to be better as compared to other treatments. Further to find out most appropriate drying condition the treated samples were subjected to three different drying methods namely cabinet drier, low temperature drier and microwave assisted convective drier. Among them the cabinet drier was found to be the best for dehydration of onion slices as it retains higher content of pungency, better drying and rehydration ratio and less NEB and also took less time for drying the product in bulk at a time. The onion powder prepared by grinding the dehydrated onion slices with the help of powder mill, was subjected for ERH study. For the storage of the onion powder the optimum RH of 50 to 55% and moisture content 4.3% were found best. The critical point and danger point for the onion powder were noticed as 9.21% and 7.23% moisture level, respectively. With regards to packaging material and storage temperature, the onion powder was packed in three packaging material of 200 g HDPE, 150 g PP and 260 g ALPE pouches and stored at ambient and low temperature for storage study. Results indicates that, packaging material of 260 g ALPE pouches followed by storage at low temperature were found best for retaining better nutritional qualities in onion powder up to six months at low temperature and four months at ambient temperature as compared to other packaging materials of 200 g HDPE and 150 g PP pouches. However the, ascorbic acid, pungency, total phenols, antioxidant activity, rehydration ratio and sensory score decreased with advancement of storage period, while moisture content, reducing sugars, total sugars and NEB increased during the storage period.
Description: T-8443
Issue Date: 2011
Appears in Collections:Theses

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