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Proceedings of Symposium on Energy Engineering in the 21<sup>st</sup> Century (SEE2000) Volume I-IV

ISSN:
1-56700-132-7 (Print)

OSMOTIC DEHYDRATION PRETREATMENT IN DRYING OF FRUITS AND VEGETABLES

Y.K. Pan
Department of Mechanical Engineering, Tianjin Institute of Light Industry, 300222, Tianjin, China

L.J. Zhao
Department of Mechanical Engineering, Tianjin Institute of Light Industry, 300222, Tianjin, China

Y. Zhang
Department of Mechanical Engineering, Tianjin Institute of Light Industry, 300222, Tianjin, China

G.H. Chen
Department of Chemical Engineering, Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong, China

Arun S. Mujumdar
Department of Chemical Engineering, McGill University, Montreal, Canada; National University of Singapore 9 Engineering Drive 1 Singapore 117576

Abstract

Several vegetables and fruits, apple, ginger, carrot and pumpkin are dehydrated under various osmotic conditions using sucrose and salt as the permeating agents. The dehydrated materials are then dried. The influence of solute concentration, process temperature and the type of solute on osmotic dehydration and further thermal drying are investigated. The nutrition loss during the osmotic process is measured using carotene as the nutrition index. The effect of calcium chloride present in osmotic solution on the product quality has also been studied. A first order kinetic model is chosen to describe the mass transfer phenomena of the osmotic process. The equilibrium value of water loss, solute gained, kinetic constants KWL and KSG under various conditions are successfully predicted by the model. The relationship between the equilibrium value and four major factors that influence osmotic process of carrot is obtained based on the experimental data. The relations between the loss constant of carotene and the solute concentration in carrot and pumpkin are obtained based on the experimental data. The qualities of dried products are better for the osmotic dehydration pretreated samples than those dried directly.