Effects of drying temperature on the flavonoid, phenolic acid and antioxidative capacities of the methanol extract of citrus fruit (Citrus sinensis (L.) Osbeck) peels

There are many active functional compounds in citrus peels, such as flavonoid and phenolic acid. Scientists tried to obtain more bioactive components from citrus peels by various methods. This research investigated the effects of different drying temperatures (50, 60, 70, 80, 90 and 100°C) on changes in the flavonoid, phenolic acid and antioxidative activities of citrus fruit (Citrus sinensis (L.) Osbeck) peels. The total phenolic and flavonoid contents of drying treated orange peels were decreased by lower drying temperature (50 and 60°C) and increased by higher drying temperature (70, 80, 90 and 100°C). Amounts of phenolic compounds in the 100°C treated sample extract were significantly higher than the amounts in the samples heated at other temperatures (P<0.05). EC₅₀ values of orange peel extracts by DPPH radical scavenging effects and ABTS^·+ scavenging effects were increased with lower drying temperature and decreased with higher drying temperature, and the values of 100°C treated sample extract were significantly lower than the samples heated at other temperatures (P<0.05). However, the chelating Fe²⁺activities of samples showed the opposite trend.