Stability of ascorbic acid in commercially available orange juices

Objective: To compare the vitamin C content of reconstituted frozen orange juice concentrates at preparation to that of ready-to-drink orange juices purchased 4 to 5 weeks from expiration. Design: Juices were unsealed and analyzed for reduced and oxidized vitamin C content at the time of purchase and reanalyzed 3 times weekly for 4 to 5 weeks. Same-lot samples of the ready-to-drink juices remained sealed after purchase and were opened for analyses at 3, 2, 1, or 0 weeks before expiration. Samples/setting: Orange juices were reconstituted frozen concentrates, ready-to-drink juice packaged in resealable, screw-top containers, or ready-to-drink juice packaged in nonresealable containers. Juices were obtained from local retailers and stored at 4°C in their original containers when appropriate. Statistical analyses performed: The reduced vitamin C content of juices analyzed repeatedly, 3 times weekly for 4 weeks, were compared using repeated measures analysis of variance. Linear regression lines were computed for reduced vitamin C in each juice over time, and differences between slopes were analyzed by oneway analysis of variance. Results: The orange juices from frozen concentrates contained 86 mg reduced vitamin C per fluid cup at initial preparation and 39 to 46 mg/c after 4 weeks of storage. Ready-to-drink juices averaged significantly lower reduced vitamin C: 27 to 65 mg/c at opening and 0 to 25 mg/c at expiration 4 weeks later. Ready-to-drink orange juices had twofold to threefold higher concentrations of oxidized vitamin C vs the orange juices reconstituted from frozen, and the decomposition rate of reduced vitamin C was similar for all juices, about 2% per day once opened. Applications: Ready-to-drink orange juices should be purchased 3 to 4 weeks before expiration date and consumed within 1 week of opening.