DEVELOPMENT AND PERFORMANCE EVALUATION OF A MULTISTORIED UNIVERSAL CABINET DRYER FOR DRYING OF HIGH MOISTURE VEGETABLES

Abstract

Development of appropriate drying technique and associated dryer are important issues for quality and stable dried vegetables. The present research was carried out to design and fabricate of a multi-storied universal cabinet dryer (MSUCD) suitable for drying of high moisture vegetables. Further, drying performance of the dryer was compared to other three conventional drying methods (sun, shade and existing cabinet) in yielding quality dried mallow (napa shakh) powder. Necessary adjustments were employed for ensuring uniform distribution of drying air flow and temperature in all trays of the drying chamber. The dryer was found to be quite satisfactory functioning for drying of 13 locally grown vegetables. Drying results revealed that shorter drying time (only 1.00 to 2.67 hr) required for drying of leafy vegetables from initial high moisture content of 93% to final moisture content of 3.78% (wb). However considerably longer drying time (6.33 to 17.67 hr) required for drying of tuber vegetables from 90.20% to 6.44% (wb) final moisture content. Lesser energy (0.87kWh/kg) required in drying of leafy vegetables whereas comparatively higher energy (5.05 kWh/kg) was found to be needed in drying of tuber vegetables by this dryer. Consequently, drying cost was lower in drying of leafy vegetables than tuber vegetables. Thermal efficiency was found to be 42.19% and 7.61% in drying leafy and tuber vegetables, respectively. The drying time required for drying of the mallow leaves were 6 hr, 48 hr, 4.25 hr and 1.33 hr for sun, shade, cabinet and MSUCD, respectively. The obtained results showed that drying methods have significant effects on functional, antioxidant and sensory characteristics of dried mallow powder. Results also revealed that significantly higher amount of bioactive compounds and their antioxidant activity were found to be retained in mallow powder dried by MSUCD compared to other drying methods. Therefore, this work suggests that the MSUCD is promising for drying of all high moisture vegetables. Moreover, this work also provided the way to design prototype as well as industrial scale multi-storied universal cabinet dryer for drying of high moisture vegetable products.