Please use this identifier to cite or link to this item: http://krishikosh.egranth.ac.in/handle/1/92589
Authors: Sahoo, Nihar Ranjan
Advisor: Mohanty, Satya Narayan
Title: STUDIES ON DIFFERENT DRYING METHODS FOR ONION (Allium cepa L.)
Language: en
Type: Thesis
Series/Report no.: Th;3789
Abstract: A Study was conducted to explore the feasibility of drying onion with some newer methods as microwave assisted convective drying, heat pump drying and combination drying methods and to compare the drying characteristics and product quality with the conventional hot air drying methods. Experiments were conducted to dry onion shreds in convective hot air drying (HAD) at 50°C (46 ± 4% R.H.), 55°C (35 ± 4% R.H.), 60°C (28 ± 4% R.H.) and 65°C (20 ± 4% R.H.), heat pump drying (HPD) viz. 35° C (32 ± 2% R.H.), 40° C (26 ± 2 %R.H.), 45° C (19 ± 2% R.H.) and 50° C (15 ± 2% R.H.) and microwave assisted convective drying at four microwave power levels i.e. 120, 240, 360 and 480 W and at air temperatures of 50, 55 and 60°C. Hot air drying at 60°C, heat pump drying at 50°C and microwave assisted drying at 240W power level and 50°C were recommended among the different conditions of drying to maintain the desired quality parameters. The drying times were observed to be 300, 360 and 75 minutes for bringing down the moisture content of onion shreds from 675.8 to 6±2.5 %(d.b.) in hot air dryer (60°C), heat pump dryer (50°C) and microwave assisted convective drying (240 W power and 50°C), respectively. Drying took place mainly under falling rate period and drying rate decreased with the moisture content of the samples in all the drying methods. Page model fitted well to all the experimental drying data for describing the thin layer drying behaviour of onion in hot air drying, heat pump drying and microwave assisted drying. The onion shreds pre-treated with potassium meta-bisulphite retained better colour of the dried product. The retention of pyruvic and ascorbic acid was more in heat pump dried samples as compared to hot air dried samples at 50°C. The quality of dehydrated onion was observed to be the best in heat pump dryer at 50°C followed by microwave assisted convective drying at 240 W-50°C combination and hot air convective drying at 60°C. HAD(60°C)-HPD(50°C) combination drying yielded product of better colour, whereas, texture, flavour and ascorbic acid retention were more in HPD(50°C)-HAD(60°C) drying method. Sulphited onion shreds dried in heat pump dryer at 50°C and stored in metallized polyester polyethylene (MPP) under ambient condition retained the quality parameters better up to 6 months of storage as compared to PET bottle. From the above study, it is recommended that onion shreds to be dried in heat pump dryer at 50°C to produce quality dehydrated product with better acceptability followed by microwave assisted convective drying at 240 W power level-50°C temperature and hot air convective drying at 60°C. Sulphited samples dried at 50°C in heat pump dryer and stored in MPP pouches is acceptable after six months of storage with substantial amount of quality retention.
Subject: Processing and Food Engineering
These Type: Ph.D
Issue Date: 2011
Appears in Collections:Thesis

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