Enzyme-mediated aldehyde change in orange juice

Abstract

Flavor stability of unheated orange juice was assessed by following enzymically the change of volatile aldehyde content of freshly extracted orange juice incubated at 30°. The aldehyde content increased linearly for 4 hr to 130% of that in the initial juice. Sodium pyruvate stimulated accumulation of aldehyde about 20-fold. Radioactivity was recovered in acetaldehyde fraction from gc of headspace of juice incubated with so-.dium pyruvate-14C. Freshly extracted juice contains active pyruvic decarboxylase (E.C. 4.1.1.1), which is still about 20% active after 1 hr incubation. If pyruvic decarboxylation were the only source of the aldehyde increase, about 1.4 ppm of acetaldehyde would accumulate in 4 hr at 30°.Citrus fruits contain numerous hydrolytic and oxidative enzymes (Kefford and Chandler, 1970). When fruit is extracted for juice, most of the enzymes are rapidly inactivated by the acid released from the vacuole. However, several enzymes retain detectable activity in fresh unprocessed citrus juices: acetylesterase (Jansen et al., 1947), alcohol dehydrogenase (Roe, 1972), pectinesterase (Mac-Donnell et al., 1945), peroxidase (Davis, 1942), and phosphatase (Axelrod, 1947). Only pectinesterase is known to

Orange juice quality with an emphasis on flavor components

“…Only a few enzymes, pectinesterase, acetylesterase, alcohol dehydrogenase, and peroxidase, remain active in fresh, unprocessed orange juice. 90 Pectinesterase via hydrolysis produces adverse quality changes in orange juice by destabilizing the cloud or the colloidal system of suspended particles which results in separation and ultimately in juice clarification. 90 -91 Acetylesterase, as well as alcohol dehydrogenase, reacts with esters, aldehydes, and alcohols, the important flavor components of orange juice, but the significance of these enzymes in determining finished juice quality is dubious.…”