Combined Osmotic and Microwave-vacuum Dehydration of Persimmon (Diospyros kaki)

Abstract

Whole fruit persimmons were dehydrated osmotically by immersion in a ternary solutions consisting of sucrose and NaCl at a constant temperature (30°C). A second-order central composite design (CCD) with two variables was used involving combinations of sucrose concentration from 30 to
60 g / 100g and NaCl concentration from 0 to 10 g / 100g. The mass transfer parameters were experimentally determined by measuring Weight Reduction (WR), Water Loss (WL) and Solid Gain (SG). After impregnation soaking for 48 h the WR and WL were more than 0.4 kg/kg and the SG was less than 0.13 kg/kg. The mathematical models as a function of osmotic solution concentration were fitted to a 2^nd order polynomial. The optimum sets were selected from the superimposed response surface plots. The best osmotic treatment condition was immersion of fruit in an osmotic solution containing 40 g/100g sucrose and 1 g/100g NaCl for 12 h 45 min to reach 35% solid content. The combined osmotic and microwave-vacuum dehydration could produce an osmo-dehydrated persimmon product which accepted by 81% of consumers and 61% of consumers would consider purchasing it.