Changes of antioxidant capacity and oxidoreductases of Saudi date cultivars (Phoenix dactylifera L.) during storage

- The total phenolic and flavonoid contents increased during storage of dates cultivars.
- The antioxidant activity assessed by DPPH and FRAP decreased threefold during storage.
- Activities of peroxidase and catalase decreased and polyphenoloxidase increased during storage.
- The enzymatic browning by oxidoreductases may be essential to character of the dates in tamer stage.

Dates harvested from date palm (Phoenix dactylifera L.) are considered as the most commonly consumed fruits in Saudi Arabia. The total phenolic and flavonoid contents, antioxidant activity and oxidoreductases of dates cv. Khalase and cv. Shishi in tamer stage during storage were investigated. The total phenolic and flavonoid contents increased during storage for 6 and 12 months at 4 °C. The antioxidant activities assessed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) decreased threefold after 12 months of storage at 4 °C. The correlation coefficient (R2) between phenolic contents, and DPPH and FRAP assays was strong. While the activities of peroxidase and catalase decreased during storage, polyphenoloxidase increased. The intensity of browning of Khalase and Shishi increased during storage at 4 °C. In conclusion, the change in antioxidant capacity during storage at 4 °C may attribute to appear new phenolic compounds with low antioxidant activity by reaction of oxidoreductases. The enzymatic browning by oxidoreductases may be essential to character of the dates in tamer stage. The dates palm even after storage at 4 °C could be a good source of antioxidants which may have healthy benefits for humans.