The affinity for oxygen of polyphenoloxidase in grapes

The influence of oxygen on the reaction of polyphenoloxidase in grapes was determined. Using crude extracts of grapes with a sufficiently high polyphenoloxidase activity on a substrate of pyrocatechol, apparentKm values for oxygen, at 25° C were calculated as 1.1 × 10−4mol (or 9% 02) for Sultana, and 1 × 10−4mol (or 8% O2) for Doradillo grapes. The importance of these figures for wine making is discussed.