EFFECTS OF DIPPING AND WASHING PRETREATMENTS ON MICROWAVE DRYING OF GRAPES

The effects of different dipping pretreatments on microwave drying of grapes war studied in a multimode cavity, Grapes pretreated with 2% et hyl oleate in 0.5% sodium hydroxide (NaOH) solution resulted in compar atively good quality raisins with lowest drying times. Pretreatment wi th 3% ethyl oleate in 0.5% NaOH solution led to similar product withou t any major advantage over the former. Grapes treated with 3% ethyl ol eate in 2.5% potassium carbonate solution took longer time to dry. Gra pes treated with only NaOH solution resulted in raisins of inferior qu ality in terms of color and appearance. The interphase mass transfer c oefficients also described the effect of these chemical pretreatments. Studies conducted on the effect of washing and time of holding after the pretreatment indicated that both of these factors had no influence on drying time.