Effect of Storage Conditions on Antioxidant Enzymes and Polyphenol Oxidase Activity of African Star Apple Juice

Abstract

This study investigated the effect of storage on both antioxidant enzymes and polyphenol oxidase activities of African star apple juice. African star apple (Chrysophyllum albidum) was sorted, washed, peeled and deseeded before milling the pulp to get fruit paste. The milled paste was then filtered to get a clear juice. The clear juice was packed in sterilized bottles before pasteurizing in a water bath at 71.2 oC for 30 minutes; after which a part was stored under refrigeration condition (6±2 oC), while the other part was stored under tropical ambient condition (28±2 oC). Catalase (CAT), superoxide dismutase (SOD) and reduced glutathione (GSH) all increased as storage period increased, with samples stored under refrigeration conditions recording higher values than those stored under tropical ambient conditions. On the other hand, the selenium-containing microsomal enzyme, glutathione peroxidase (GPx), registered an inverse relationship with storage period at both conditions. Polyphenol oxidase optimal thermal activity was observed at 80 oC and that of pH was at 7, whereas the enzyme was more stable at 40 oC at all stages and conditions of storage tested. The study also showed that polyphenol oxidase was more active when purified partially, compared to the crude enzyme. In conclusion, polyphenol oxidase can be isolated from African star apple juice stored under different conditions.