DESIGN AND DEVELOPMENT OF TUNNEL TYPE SOLAR DRYER FOR DEHYDRATION OF ONION AND AMLA
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Date
2015-08-12
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK, BENGALURU
Abstract
Solar tunnel dryer of 6x3x2.7 m (LxWxH) with galvanized frame structure
was constructed and covered with 200 micron UV-stabilized LDPE sheet. Two fresh
air inlets of 0.6 x 0.3 m size and two exhaust fans each of 9 inches dia and 50 watt
capacity were installed at the rear side and front side of the dryer, respectively. The amla
pretreated with 2 per cent sodium chloride and 0.1 per cent potassium meta-bi-sulphite
and onion pretreated with 0.25 per cent potassium meta-bi-sulphite were subjected for
drying. In solar tunnel dryer, the drying required 12-15 h and 13-14 h for various pretreated
amla segments and onion slices to reduce from moisture content of 422.32-
521.46 per cent (d.b.) to a safe moisture content of 17.01-17.39 per cent (d.b) and from
moisture content of 572.92 -797.29 per cent (d.b.) to attain a safe moisture content of
6.08-6.24 per cent (d.b), for amla and onion, respectively. Chemical analysis indicates
that the quality of solar tunnel dried products are superior to open sun dried products .The
vitamin-C retention was found to be highest (125.68 mg/100g) in untreated amla samples
dried in solar tunnel dryer. The highest total phenolics, FRAP was found to be 325.09
(μg/g) and 1617.09 (μg/g), respectively in 0.25 per cent KMS pre-treated onion dried in
solar tunnel dryer. The payback period for amla is 6 months and for onion it is 9 months.
The results showed that the rehydrated products could be well utilized for substituting the
fresh product in off season.
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