Effect of storage on the content of polyphenols, vitamin C and the antioxidant activity of orange juices

The effect of time and temperature on the content of vitamin C, total polyphenols and individual phenolic compounds as well as on the antioxidant activity of two commercial orange juices was studied. The polyphenol content was determined using Folin-Ciocalteu and HPLC methods. The two methods, SPE versus direct injection following a simple treatment of samples, were compared to assess two techniques of sample preparation. For antioxidant capacity determination, DPPH and FRAP assays were used. All analyses were carried out for fresh juices and after storage at 18, 28 and 38 degrees C for 2, 4 and 6 months. It was found that vitamin C and free and conjugated hydroxycinnamic acids were the most affected by both duration and temperature of storage. The decrease in the content of polyphenols and vitamin C upon storage was reflected by the decrease in the antioxidant capacity of orange juices. Small changes in flavanone content were observed, indicating high stability of these compounds upon storage.