Peeling of Walnut Kernel by Vacuum Freeze-Drying: An Analytical and Experimental Study

Peeling of walnut kernel by vacuum freeze-drying was mathematically modeled, theoretically evaluated in heat/mass transfer analysis and experimentally studied.The peeling mainly comprised the pre-freezing, sublimation drying and desorption drying.The influence of the sublimation drying temperature and time on the color, nutrition and taste of the peeled walnut kernel was investigated.The analytical results show that the sublimation drying time had a major impact.To be specific, as the sublimation drying time increased, walnut kernel could be peeled increasingly easy. Peeled and dried under the optimized conditions:a rehydration time of 2 h, a sublimation time of 4 h, a desorption drying temperature of 30℃ and time of 4 h, the dried and completely peeled walnut kernel had natural color, nutrition and taste.The analytical and experimental results were in good agreement.