Direct Enzymatic Conversion of Lactose to Acid: Glucose Oxidase and Hexose Oxidase

The conversion of lactose directly to an acid by glucose oxidase and hexose oxidase as a method of milk acidification was studied. Under the appropriate conditions, both enzymes demonstrated the capability to catalyze the conversion of sugar in milk to an acid, producing coagulation. A uniform distribution of oxygen under quiescent conditions was essential for the reaction and could be accomplished with the addition of hydrogen peroxide in the presence of catalase. Commercial samples of glucose oxidase caused a gradual decrease in pH of skim milk containing added glucose or lactase, (beta‐galactosidase). Hexose oxidase, which can react with galactose and lactose as well as glucose, produced acid at a very slow rate in skim milk alone. When lactase was incorporated into the milk, the rate of reaction increased significantly.