Effect of aeration on extracellular enzyme synthesis by psychrotrophs growing in milk during refrigerated storage

Aerating milk markedly reduced proteolysis but increased lipolysis during storage at 6°C. The increase in lipolysis was due to native milk lipoprotein lipase, and aeration conditions could be modified to overcome this deleterious effect. The decrease in proteolysis was due primarily to a decrease in the amount of protease synthesized rather than a change in the bacterial flora of the milk. It was shown that protease and lipase production by psychrotrophs growing in milk was subject to catabolite repression by glucose. Differences in levels of certain metabolites produced by bacteria growing in aerated and non-aerated milks may be a factor contributing to the decrease in protease activity.