Effect of heat treatment on polyphenol oxidase and peroxidase activities in Algerian stored dates

Abstract

Effect of heat treatment (55°C/20 min) on polyphenol oxidase (PPO) and peroxidase (POD) activities and total phenolic compounds was investigated in Algerian dates (Deglet Nour variety) at Tamar (fully ripe) stage and in dates stored for 5 months at ambient temperature and in cold storage (10°C). Results obtained showed a high percentage of total phenolic compounds. These compounds decreased weakly as the fruit advanced in storage at ambiant temperature, whereas, they are still higher in heat treated and cold stored dates. Heat treatment did not show a significant effect on phenolic compounds variation. Deglet Nour dates showed that there was a decrease in both POD and PPO activities during storage for either heat treated and non-treated dates samples. Whereas, PPO activity was weaker in chilled dates comparatively to those stored at ambient temperature. Peroxidase activity showed a similar trend where a decrease was observed in all samples during storage, particularly in heat treated dates. In all cases, heat treatment seems to benefit reducing POD activity, whereas a relative stability in PPO activity was noted.