Contributions of the heat-resistant lipase of psychrophilic bacteria to off-flavors in pasteurized milk

The importance of psychrophilic bacteria is linked to their ability to grow at refrigeration temperature. Their importance to the dairy industry has been accentuated by the advancements in refrigeration facilities, increased regard for keeping quality, and longer holding times resulting from every other day pickup, less frequent home deliveries, and transporting over greater distances. The psychrophiles have long received the attention of butter and cottage cheese manufacturers and much of the present knowledge of the psychrophiles was received from these products; recently much concern has been shown to market milk processing with regard to the contamination by the psychrophiles.

The psychrophiles are primarily responsible for limiting the keeping quality of milk and fluid milk products in which they may produce a wide variety of spoilage defects. Despite the obvious and long importance of lipolytic activity of bacteria in dairy products, other than demonstration of the presence of lipolytic bacteria (81) or the observation that a particular bacterium produced rancidity, very little work has been directed toward the study of lipolysis by psychrophilic bacteria. Some of the species of the genus Pseudomonas produced lipase which was found to be heat stable (52).

The present study was undertaken to determine the effects of the heat resistant lipase of the psychrophilic bacteria on the flavor of pasteurized milk stored at refrigeration temperature (4°C.).