a b s t r a c tA small test apparatus was made for partial melting of ice at controlled conditions in temperature and stirring speed. Ice cubes from 10 wt% sucrose were partially melted in this apparatus at 4 temperature and 4 stirring speeds. At the lower temperature with relatively faster stirring speed, the initially-melted fractions effectively contained the higher concentration of solute than the later-melted fractions. The partial ice-melting technique was combined with progressive freeze-concentration (PFC) to improve the yield in PFC. Apple juice with 13.7°Brix was concentrated up to 25.5°Brix by PFC using a tubular ice system. Then, the partial ice-melting was applied for the ice formed by PFC to improve the yield from 63.8% to 85% by recovering the initial 30% melted fraction. The partial ice-melting was also applied to pear (La France) juice flavor condensate. After 2.36 times concentration of flavor component (butyl acetate) by PFC, the yield was improved from 86.7% to 95% by recovering the initial 35% melted fraction in the partial ice-melting process. Partial ice-melting technique will overcome the major drawback of PFC, in which the yield decreases with an increase in solute concentration because of the solute inclusion in the ice.
Progressive freeze-concentration of 3 to 30% sucrose solutions were carried out using a small cylindrical apparatus. The solute concentration distribution in the ice phase was determined by cutting the ice formed into fractions and analyzing the solute concentration in the fractions. The solute concentration in the ice phase was found to increase as the concentration process progressed. From the solid phase analysis, the corresponding liquid phase concentration was estimated in the concentration process and an effective partition coefficient, K, was determined. K was also obtained from the concentration polarization theory. To this purpose, the limiting partition coefficient, K 0 , was obtained, then K was determined from the concentration polarization theory. K obtained by the two methods agreed well. K increased with an increase in solute concentration of sucrose, which corresponds to the higher incorporation rate of solute into the ice phase in progressive freeze-concentration.
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