14A-37 |
Use of high-pressure processing to extend the shelf life of pasteurized fluid milk products |
E. G. ADAMS and W. J. Harper. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 The shelf life of commercial pasteurized milk is limited to 10 to 14 days due to post-pasteurization contamination by psychrotrophic microorganisms. Although UHT treatment significantly increases shelf life, it also creates a noticeable flavor difference compared to pasteurized milk. Non-thermal processes, such as high-pressure processing (HPP), have been shown to reduce microbial counts in foods. HPP may extend the shelf life of milk by reducing psychrotrophic bacteria counts without creating off-flavors from heat or altering physical properties. The objective was to extend the shelf life of pasteurized milk using high-pressure treatments to eliminate post-pasteurization contamination by psychrotrophic bacteria. Commercial samples of pasteurized 2%, skim and chocolate milk were high-pressure treated at 400 and 800 MPa below 30ºC for 10 minutes in a cold isostatic press. The samples contained psychrotrophic bacteria counts ranging from 104 to 107 cfu/ml. Other commercial samples of pasteurized 2% and chocolate milk containing less than 40 cfu/ml were high-pressure treated at 400, 600 and 800 MPa below 30ºC for 10 minutes. The samples were enumerated for psychrotrophic growth on days 0, 10, 20 and 30 using the International Dairy Federation enumeration technique. HPP reduced the psychrotrophic bacteria counts in the milk samples with high initial counts by 5 log for skim and chocolate milk and 2 log for 2% milk. After 20 days of storage each sample had psychrotrophic counts above 6*104 cfu/ml. The samples with low initial counts before HPP contained below 6*104 cfu/ml after 20 days of storage, but above 6*104 cfu/ml after 30 days. Average particle size and color of the milk were not significantly altered by the treatments. High-pressure treatments (400, 600, 800 MPa) extended pasteurized milk shelf life more than 10 days beyond untreated pasteurized milk and resulted in a longer extension for fresh milk than milk near its expiration date.
Session 14A, Dairy Foods: General developments in dairy technology I
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