STUDIES ON DEHYDRATION OF ONION AND TOMATO USING SOLAR TUNNEL DRYER
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Date
2018-07
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UNIVERSITY OF HORTICULTURAL SCIENCES, BAGALKOT
Abstract
An experiment entitled “Studies on dehydration of onion and tomato using
solar tunnel dryer” was conducted in the Department of Post Harvest Technology,
College of Horticulture, Bagalkot, Karnataka during the year 2017-18. Fresh onion
and tomatoes were prepared for dehydration by cutting into different size/shapes
(S1 - Dices and S2 - Slices in case of onion and S1 - 0.5 cm slices, S2 -1 cm slices and
S3 - Longitudinal quarters in case of tomato) and subjected to different chemical pretreatments
for a specified duration. Onions and tomatoes thus prepared were
dehydrated in solar tunnel dryer and analyzed for different physico-chemical qualities.
In dried onion, the slices (S2) recorded significantly minimum moisture
content (13.80%), minimum drying time (57.17 hours), higher rehydration ratio (2.98)
and significantly higher sensory score. Among pre-treatments, T2 (0.25% KMS for 15
min), T3 (0.1% KMS + 2% CaCl2 for 5 min) and T6 (0.5% Na2S2O5 for 20 min) were
found superior with respect to various physico-chemical and sensory properties.
Onion slices dehydrated after pre-treatments (T2, T3 and T6) were subjected to storage
in stand on PE-pouches for three months. During storage, T6 recorded significantly
minimum moisture (initial-11.38% and 3 MAS-14.02%) and NEB value (initial-0.08
and 3 MAS-0.15), significantly higher pungency (initial-6.35and 3 MAS-4.83) and
maximum sensory score for overall acceptability (initial-8.56 and 3 MAS-8.06).
In dried tomatoes, the S3 (Longitudinal quarters) recorded significantly
maximum recovery (5.01), titratable acidity (0.80%) and lycopene content (3.23
mg/100 g) followed by S2 (1cm). Most of the physico-chemical and sensory
properties of dried tomatoes due to pre-treatments and control did not show
significant differences. Therefore, tomatoes (S2 and S3) dehydrated without any pretreatment
(T1-control) were packed in stand on PE-pouches and stored for three
months under ambient conditions. Though S3 tomatoes absorbed more moisture and
higher NEB values during storage, they were found better in retention of titratable
acidity (Initial-0.77 and 3 MAS-0.48) and lycopene (Initial-3.04 and 3 MAS-2.65)
representing characteristic taste and nutritional benefits associated with acidity and
lycopene respectively. Therefore T6 of S2 in onion and T1 (Control) of S3 in tomato are
concluded as best for dehydration under solar tunnel dryer.
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