Effects of dipping and washing pre-treatments 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% ethyl oleate in 0.5% sodium hydroxide (NaOH) solution resulted in comparatively good quality raisins with lowest drying times. Pretreatment with 3% ethyl oleate in 0.5% NaOH solution led to similar product without any major advantage over the former. Grapes treated with 3% ethyl oleate in 2.5% potassium carbonate solution took longer time to dry. Grapes treated with only NaOH solution resulted in raisins of inferior quality in terms of color and appearance. The interphase mass transfer coefficients 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.