Photostability of vitamin C in industrialized fruit juices and isomers determination by HPLC-DAD

L-ascorbic acid (LAA) and D-isoascorbic acid (DIAA) are two of the most important antioxidants in industrialized fruit products as mixed fruit juices, fruit concentrates, and jams, in which they are added as antioxidants and as a nutrient. Despite that, LAA may undergo oxidative- and photo-degradation during storage, compromising its concentration and activities in these food products. In this work we aimed to optimize a method for the identification and quantification of LAA and DIAA by high performance liquid chromatography with diode-array detection (HPLC-DAD) using a NH2 column and a pre-heated mobile phase. A further aim was to investigate if food packing actually protects fruit juices against LAA photodegradation. For the UV photostability test, samples were UV-irradiated at 1,416 μW·cm−2, at 28 ±°C, and with a radiation energy above 200 W·h·m−2. The optimized HPLC method provided complete peak resolution of vitamin C isomers in less than nine min run-time. At the end of photostability tests with fruit juices and jellies packaged in polyethylene terephthalate and glass bottles or flasks, L-ascorbic acid was undetectable, suggesting that the packages did not provide effective protection against vitamin C photodegradation. To the best of our knowledge, vitamin C photostability in fruit products was previously unreported.