Reactivation of the Lactoperoxidase System during Raw Milk Storage and its Effect on the Characteristics of Pasteurized Milk.

The Lactoperoxidase (LP) system was activated periodically during raw milk storage, and after pasteurization. Raw milk was stored at 4°C for 4, 6 or 8 d, and after pasteurization at 8 or 16°C, until a laboratory-trained taste panel reported the presence of off-flavors. When treated milk was stored raw for 4 d, then pasteurized it maintained its quality for 12 d at 8°C; pasteurized control milk had a shelf-life of 9 d only. Shelf-life of pasteurized milk stored at 16°C after pasteurization was 6 d for LP-treated and 5 d for control milk. LP-treated milk that was stored raw for 6 d retained its quality after pasteurization for 11 d at 8°C and 5 d at 16°C, while shelf-life for control milk of this experiment was 5 d at 8°C and 1 d at 16°C. When storage of raw milk was extended to 8 d, control milk showed off-flavors right after pasteurization, whereas LP-treated milk developed a "stored" or "unclean" taste after 1 d of pasteurized storage. Reactivation of the LP system is proposed to extend the shelf-life of pasteurized milk, when raw milk storage for over 2 d is necessary.