Kinetics of ascorbic acid thermal degradation in Valencia orange juices and evaluation of its shelf life

Abstract

Ascorbic acid is a well-known natural antioxidant which is widely distributed in nature, especially in green plants. Its traditionally known sources are citrus fruits like orange. This vitamin acts as an efficient radical inhibitor and it has been used as a food additive. Moreover, it presents antioxidant activity and contributes for the prevention of certain types of cancer. Ascorbic acid is also used as an index of nutritional quality of fruits and vegetables, due to its sensibility to different kinds of degradation in food processing and subsequent storage. Thus, the study of ascorbic acid degradation kinetics is important to raise information that allows estimating the quality changes that occur during the storage of food products. The purpose of this research was to evaluate the thermal degradation kinetics of ascorbic acid in Valencia orange juices and to quantify the effect of water activity on its rate of loss upon storage. Ascorbic acid content was determined by titration with 2,6 dichlorophenol indophenol. Its degradation as a function of storage time was studied at different temperatures during a period of 14 days of storage. Reaction constant rates (k) and the order of reaction (n) were determined through regression analysis of experimental data. Higher coefficient of determination (R2) indicated that a first-order reaction model fits closely well to data obtained in this study. In general, it was observed that increasing temperature and water activity led to increasing losses of ascorbic acid. A direct equation for the estimation of the shelf life of the juice with respect to ascorbic acid losses at any specified temperature and degradation rate has been derived.