Yield improvement in progressive freeze-concentration by partial melting of ice

Abstract

Progressive freeze-concentration (PFC) was applied for the concentration of sucrose solutions with various concentrations (0.3–40%), a model pear (La France) flavor solution, tomato juice (5.3 Brix) and apple juice (12–15 Brix). When the solute concentration was low with low osmotic pressure as in the case of the model pear flavor solution, the apparent partition coefficient (Kapp) between the ice and the concentrated liquid phase was low to give a high yield. For samples with high solute concentrations, however, Kapp increased with an increase in solute concentration to reduce the yield in PFC operation. In this case, the partial melting of ice was effective. In this method, the ice crystal formed after PFC was melted gradually with time to collect the melted fractions with intervals. Then the initial fractions were found to contain the higher amount of solute. Therefore, the yield could be improved to a necessary level (>90%) by recovering these fractions with the higher solute concentration. The recovered melted ice fraction may be mixed with the feed in the succeeding batch of PFC operation to avoid dilution of the concentrate. The partial ice melting will extend the practical applicability of PFC substantially.