QUALITY CHANGES DURING STORAGE IN KOREAN CLEAR PEAR JUICES CONCENTRATED BY THREE METHODS

Pears of Shingo variety were coarsely ground, and subjected to heat treatment by HTST (high temperature short time) and pectinase treatment to produce a cloudy pear juice. The pear juice was then treated with Viscozyme, gelatin and bentonite, and filtered through an ultrafiltration membrane to produce a clear pear juice. The clear pear juice was concentrated to 3 to 5 fold by vacuum evaporation, freeze concentration, and reverse osmosis methods. The concentrates were diluted to 10° Brix and stored at 4C for 15 days. The single strength juice was evaluated for color, turbidity, heat stability, and sensory preference at 5 day intervals during storage. The pear juice concentrated by the three methods showed only small differences in quality. While the clear pear juice with added ascorbic acid had no quality changes at 4C after 15 days' storage, that without the addition of ascorbic acid resulted in some deterioration in browning, turbidity and heat stability after 10 days' storage. There were small, but significant flavor differences among clear pear juices concentrated by evaporation, freeze concentration and reverse osmosis.