Whole pomegranates with rinds were processed into juice and then concentrate. Effects of cold clarification and storage temperatures (−23C, 5C, 12C and 20C) on anthocyanins (ACNs), ACN composition and color were determined. Major ACNs in pomegranate juice concentrate (PJC) were identified as cyanidin-3,5-diglucoside (47.9%), delphinidin-3,5-diglucoside (23.2%) and cyanidin-3-glucoside (18.5%). Diglucosides were more stable than monoglucosides during storage. ACN degradation and polymeric color formation were fitted to first-order reaction models. Higher storage temperatures increased the rate of ACN degradation and polymeric color formation in PJCs. Good correlation (r = −0.988) was found between ACN degradation and polymeric color formation during storage. Rate of ACN degradation and polymeric color formation were slower in the PJC obtained from unclarified juice than PJC obtained from clarified juice during storage.
There has been great interest in pomegranates and their products for their potential health benefits due to their impressive antioxidative properties, which are highly correlated with their polyphenol content, including tannins and ACNs. During pressing of pomegranates, polyphenols especially high molecular weight tannins present in the rinds pass to the juice. And excessive polyphenols cause haze and sediment formation, astringent, taste and color loss. This is serious industrial problem in the production of clear pomegranate juice. Attractive red-violet color of pomegranate products is due to their ACN contents. However, ACNs are unstable and susceptible to degradation leading to a brownish color during juice processing and storage. Results of this study showed that clarification with gelatin as well as high storage temperatures adversely affected the ACNs of pomegranate juice concentrates (PJCs). Therefore, PJC should be produced from unclarified juice and frozen-stored. The reconstituted juice should then be cold-clarified right before marketing.