Effect of Temperature and Pretreatment On Drying Characteristics of Onion

Abstract

The present study was carried out to investigate the drying kinetics of onion slices during tray drying and the effects of process on parameters during tray drying such as pretreatment and temperature of drying on drying kinetics, colour, pungency and rehydration ratio were studied. Untreated and treated sample were dried at 50'C, 60 'C and 70'C and drying time were found 330, 270 and 210 min for untreated sample where as drying time for treated sample were found 240,210,160 min. This showed that drying time decreased with increase in temperature. It showed that treated sample took less time in drying. Measurement of Color of untreated onion sample in the terms of average RGB value were 126.69, 113.20 and 108.54 at 50'C, 60'C, 70'C respectively . . Average RGB value of treated onion slices were found 170.28, 137.70 and 133.61 at 50'C, 60'C,70'C respectively. It reve aled that treated samples showed light colour compared to untreated sample but both sample showed colour increased with the increase in temperature. The treated samples with 5.46, 5.32 and 5.02 j.Jmol g-1 value of pyruvate content at 50'C, 60'C and 70'C respectively showed a higher flavour content than the untreated samples with 4.92, 4.87,4.75 !Jmolg-1 value of pyruvate content at 50'C, 60'C and 70'C respecti vely and result stated that the pyruvate content decreased with increase the temperature. Other quality parameter Rehydration ratio observed an increase in rehydration ratio with increase in drying temperature. The value of rehydration ratio were found 5.33, 5.51 and 5.66 at 50'C, 60'C and 70'C respectively for untreated sample where as value of rehydration ratio for treated sample were found 5.99, 5.07 and 5.48 at 50'C,60'C and 70'C respectively. It was also observ ed as an increase in rehydration ratio with increase in drying temperature. Quality of dried onion slice in respect to colour, pungency and rehydration was superior of treated sample at 60'C.