The growth response of coliform bacteria in milk to an increase of 5°C after refrigerated storage

The milk industry strives to offer the public safe and nourishing products. Improvements in milk processing has been made through the years and without a doubt will continue to be made in the future. Pasteurization by heating is the present method of ensuring that milk is free of pathogenic organisms. The phosphatase test is used for determining whether or not milk has been properly pasteurized.

Even if milk has been properly pasteurized, there is the possibility of recontamination through careless handling of pasteurized milk before it is bottled. At the present time, the best means of determining recontamination after pasteurization is the test for coliform bacteria.

"The Coliform Group includes all aerobic and facultative anaerobic, Gram-negative, non spore-forming bacteria which ferment lactose with gas formation" (28). This Group hereafter will be referred to as "coliforms''.

There has been considerable work done on coliforms but still there are questions that have not been answered. Studies have been conducted on their resistance to pasteurization and growth at refrigeration temperatures but still their growth in milk has not been fully explained.

The present milk marketing program creates problems that were not faced a few years ago. Every other day pick-up at the farm, three times a week retail delivery to the consumer and five work days a week are present day operations, any of which may add one to four days to the age of the products. Generally, it is accepted that there will be little or no bacterial growth at 35-40°F during the first 48 hours of storage. Longer storage may result in some bacterial growth. The rate of growth will depend upon the types of organisms present and may be influenced considerably by only a few degrees increase in the storage temperature.