REDOX STATE OF NICOTINAMIDE-ADENINE DINUCLEOTIDES IN CITRUS FRUIT

Juice vesicles from mature and immature orange and grapefruit were examined for distribution of the nicotinamide-adenine dinucleotides as the oxidized and reduced forms: NAD, NADP, NADH, and NADPH. Enzymic assay of these oxidoreductase coenzymes in extracts from the juice vesicles gave the following average values in nanomoles per 10 grams of vesicles; NAD, 60 to 118; NADH, 8.1 to 25; NADP, 7.9 to 12; and NADPH, 12 to 18. These values are comparable to concentrations of the coenzymes in apple and pear pulp, and are in general agreement with concentrations reported for metafa olically active plant and animal tissues. The results suggest that citrus fruit has coenzyme capability to support synthesis of oxygenated compounds which contribute to flavor. The NADHNAD ratio in orange and grapefruit juice increased with fruit maturity and was higher in freeze-thawed grapefruit. This increase with maturity probably reflects changes in oxidoreductase activities accompanying the Brix-acid ratio increase. © 1969, American Chemical Society. All rights reserved.