Ultraviolet-Induced Oxidation of Ascorbic Acid in a Model Juice System: Identification of Degradation Products

• Published in: Journal of agricultural and food chemistry Vol. 59; no. 15; pp. 8244 - 8248
• Main Authors: Tikekar, Rohan V, Anantheswaran, Ramaswamy C, Elias, Ryan J, LaBorde, Luke F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10-08-2011
• Subjects: ascorbic acid; Ascorbic Acid - chemistry; Beverages - analysis; Biological and medical sciences; Chemical Changes Induced by Processing/Storage; dehydroascorbic acid; electron paramagnetic resonance spectroscopy; Food industries; free radicals; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; juices; malic acid; Models, Chemical; oxidation; Oxidation-Reduction - radiation effects; ultraviolet radiation; Ultraviolet Rays; ultraviolet light processing; ascorbic acid; ultraviolet radiation processing; nonthermal food processing; electron paramagnetic resonance spectroscopy; apple juice; Ascorbic acid; Fruit; Vitamin; Fruit product; Identification; Fruit juice; Apple; Ultraviolet radiation; Light; Models; Oxidation; Electron paramagnetic resonance; Degradation product; Food
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf201000x

Degradation products of ultraviolet (UV-C, 254 nm) treated ascorbic acid (AA) are reported. Analysis by high-performance liquid chromatography–mass spectroscopy (HPLC-MS) conducted in a 0.5% malic acid model juice system (pH 3.3) demonstrated increased degradation of AA above untreated controls with concomitant increases in dehydroascorbic acid (DHA) and 2,3-diketogulonic acid (DKGA) levels. Electron spin resonance (ESR) spectroscopy studies, conducted in phosphate buffer (pH 7.0) to increase detection sensitivity, demonstrated that ascorbyl radical (AA•) formation occurs simultaneously with AA degradation. Consistent with a previous study in which UV treatments were shown to accelerate dark storage degradation, AA• radicals continued to form for up to 200 min after an initial UV treatment. Results from this study suggest that the mechanism for UV-induced degradation is the same as the general mechanism for metal-catalyzed oxidation of AA in juice.