Characterization of vacuum dried onion slices

Abstract

Assessment of various quality parameters of vacuum dried onion, with or without pretreatment was attempted. Colour, flavor and rehydration ratio were analyzed and compared with those of convective air drying. Tissue microstructure images of dehydrated onion were studied and compared with convective air drying and microwave drying, with the help of scanning electron microscopy. The texture of dried onion was measured in terms of hardness, cohesiveness, springiness, gumminess and chewiness using texture analyzer. All these parameters were higher in case of treated samples compared to untreated ones. True density and thermal conductivity of vacuum dried onion were assessed with the changing moisture content. Colour, flavor and microstructure of vacuum dried onion were better than convective air drying. True density was found less compared to hot air dried product however thermal conductivity was almost comparable. The vacuum drying method for onion was found suitable over convective air drying which is normally practiced commercially.