Investigation and comparsion of natural and Mechanical Drying process of North Khoozestan Onion varieties
2004
Soleimani, Majid
Drying process with decrease of moisture content and water activity(aw) promotes onion storability which is resulted by limiting microbial , chemical and biochemical reactions . In this study , for comparing natural drying methods with mechanical method and also for selecting a suitable variety , a factorial experiment on the basis of a complete randomized design with 3 factors including drying method (sun drying , shade drying and drying with cabinet dryer) , onion variety(local Ramhormoz variety , Perimavera , Texas and Savana sweet) and effective evaporation area (at 2 levels of 4.22 cm2/g and 4.74 cm2/g) was performed . The results from experiments were compared using Duncan's multiple range test at 1% statistical level . The results showed that Ramhormoz had the highest efficiency of dried material , vitamin C and also the highest energy saving . Among the drying methods , mechanical method(cabinet dryer) resulted in the best color( highest L value in Hunterlab system) , the least drying time , the least total (microbial) count and the least loss in vitamin C in comparison with the other methods . Between the two natural methods , sun-drying was better than shade-drying method except for its high effect on decrease of vitamin C . But in Overall, natural methods contaminated the dried product that made it unuseable . Also the results indicated that the increase of effective evaporation area reduced drying time and the loss of vitamin C significantly . Calculation and drawing of drying rate curves on the basis of drying curves , indicated that the critical points of the mentioned varieties (except for Ramhormoz) were between 8 and 10(decimal dry basis) and there was not any critical point in drying rate curves of Ramhormoz variety. Also it was indicated that the increase of effective evaporation area causes a little decrease in critical point and consequently decrease of drying time.
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