Estudo da fotoestabilidade e quantificação do ácido L-ascórbico e D-isoascórbico em produtos processados a base de frutas por cromatografia líquida de alta eficiência

Abstract

Vitamin C is one of the most important water soluble vitamins, it is widely used in processed fruits, for enrichment or as an antioxidant. The generally found isomers of vitamin C in processed products are L-ascorbic acid and D-isoascorbic acid, being easily degraded in the presence of various factors such as light and oxygen. Photo-stability studies are needed to confirm that products exposed to light and containing vitamin C can maintain their integrity throughout shelf life. The objective of this work was to evaluate photostability and to develop a methodology for the determination of the L-ascorbic and D-isoascorbic acid isomers in processed fruit products. Adaptation was performed using the Bui-Nguyên (1980) methodology for quantification of L-ascorbic and D-isoascorbic acid by high performance liquid chromatography and DAD detection. The extraction was of liquid-solid and / or liquid-liquid type using 3% phosphoric acid solution, centrifugation and filtration. A NH2 (150 x 4.6 mm) 3μm normal phase column was used with isocratic elution using acetonitrile and monobasic potassium phosphate buffer (0.005 mol.L-1) pH 4.8 and temperature of 30°C in the ratio 80:20 v/v, respectively. For the evaluation of the photostability a non-commercial chamber was used, where the samples were exposed according to RDC nº 45/2012 of ANVISA. UV/VIS spectrophotometry analysis was performed for PET packaging and infrared vibration spectroscopy for PET and glass packaging. The proposed method showed to be sensitive to the standards presenting LD 0.0092 μg.mL-1 and 0.0131 μg.mL-1, and LQ 0.0278 μg.mL-1 and 0.0397 μg.mL-1 for acid D-isoascorbic and L-ascorbic, respectively. L-ascorbic acid was measured in the range of 0.29 to 12.01 mg.mL-1 in the samples, and the presence of D-isoascorbic acid was not detected. Exposure to visible light did not lead to degradation of L-ascorbic acid. However, in the exposure to UV radiation L-ascorbic acid was completely degraded, even the products were packed in safe packaging, allowing rethinking of guidelines for food fortification.