700. Factors influencing the activity of cheese starters. The role of milk peroxidase

Abstract

1. Certain starter cultures have been found to be inhibited in the presence of milk peroxidase. 2. A high correlation has been established between the inactivation of milk peroxidase and of the inhibitory action by use of critical values of any of the following: temperature, pH, concentration of either sodium azide or hydrogen peroxide. 3. The inhibitory action can be overcome by the addition of certain reducing substances such as cysteine and sodium hydrosulphite. 4. The inhibitory action is exhibited by the corresponding separated milk and whey. 5. It is suggested that this inhibition may be due to the formation of a specific inhibitory oxidation product having a quinonoid structure. 6. The addition of 1–2% of pasteurized milk or whey to autoclaved milk caused total inhibition, whereas such additions to milk heated to 190° F. showed no such effect. This is attributed to the presence of SH groups in the latter milk capable of reducing the oxidation product. 7. It is suggested that the inhibition due to peroxidase is identical with that ascribed to lactenin 2, and that the inhibition described in our previous paper as due to ‘agglutinin’ is identical with that ascribed to lactenin 1.