Kinetics of moisture transfer during air drying of blanched and/or osmotically dehydrated mango

The effect of previous blanching and/or osmotic dehydration (at atmospheric pressure or in vacuum) with glucose syrups on the kinetics of water transp ort during the first falling rate period of air drying of mango at 60 degre esC was investigated. Both pre-drying treatments decreased strongly the eff ective moisture diffusivity (D-eff) calculated with Fick's second law. For osmotically concentrated fruit at atmospheric pressure, the increase in glu cose concentration of the immersion solution decreased the drying rate. D-e ff values were similar for mangoes predehydrated to a(w) 0.97 by vacuum or atmospheric osmosis, but previous blanching slightly decreased the D-eff va lue for vacuum treated slices compared with those osmotically dehydrated to the same a(w), at atmospheric pressure. The air drying behaviour of blanch ed and/or osmotically dehydrated mangoes was ascribed to glucose uptake dur ing the impregnation step, volume shrinking, low modification of cell wall resistance to water flux by the pretreatments and/or gelatinization of star ch and denaturation of protein - carbohydrate mucilage. (C) 2001 Elsevier S cience Ltd. All rights reserved.