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Pasteurization, low temperature Processing and Storage of Milk

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Pasteurization or pasteurisation is a process in which certain packaged and non-packaged foods are treated with mild heat, usually less than 100 °C, to eliminate pathogens and extend shelf life.
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Pasteurization, heat-treatment process that destroys pathogenic microorganisms in certain foods and beverages. It is named for the French scientist Louis Pasteur, who in the 1860s demonstrated that abnormal fermentation of wineand beer could be prevented by heating the beverages to about 57° C (135° F) for a few minutes. Pasteurization of milk, widely practiced in several countries, notably the United States, requires temperatures of about 63° C (145° F) maintained for 30 minutes or, alternatively, heating to a higher temperature, 72° C (162° F), and holding for 15 seconds (and yet higher temperatures for shorter periods of time). The times and temperatures are those determined to be necessary to destroy the Mycobacterium tuberculosis and other more heat-resistant of the non-spore-forming, disease-causing microorganisms found in milk. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time offood.

Low temp processing and storage of milk

The effect of low temperature storage and milk quality on cheese yield was investigated. Raw milk was stored at 5, 7.5, and 10°C; grade A milk was stored for 6 to 12 d and manufacturing grade milk for up to 6 d. At 1-d (manufacturing grade) and 2-d (grade A) intervals, aliquots from each treatment were pasteurized and manufactured into cheese, and the resulting yield was compared with that obtained on d 0 for manufacturing and grade A milks, respectively. Each treatment was terminated when stored milk coagulated when pasteurized.

Increase in total bacterial count ranged from one log cycle for high count manufacturing grade milk to more than three log cycles for low count grade A milk. Similar changes were observed for proteolytic and psychrotrophic populations. As stationary populations were approached, essentially all organisms were psychrotrophic, and most were proteolytic and lipolytic. Cheese yield was affected by initial psychrotrophic populations and length of time raw milk was stored. Recovery of cheese solids decreased by approximately .

5% for manufacturing grade milk per day of storage up to 4 d. Further storage increased the loss of cheese solids, and loss of cheese yield correlated with increase in bacterial population. Yield loss appeared to be due to exocellular enzymes causing breakdown of proteins and fats. Protein degradation was accompanied by increased moisture in the curd. Cheese quality decreased as psychrotrophic populations increased. After pasteurization high count stored raw milk contained enough psychrotrophs to dominate the aging process, producing gassy unclean cheese. Stored milk cheese had a weak body with bitter flavors typical of that produced by heat-stable proteolytic enzymes.

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