Abstract
By-products of Orange (Citrus sinensis (L.) Osbeck) juice processing are that are rich in flavonoids. This study investigated changes in total phenolic and flavonoid concentrations and antioxidative activities of orange peel methanol extracts in response to various heating times (0, 30, 60, 90, 120, 150 and 180 min) at 100°C, after a 48-h drying treatment at 50°C. The total phenolic and flavonoid contents of the 0 min heat-treated peel methanol extract (T0) were 21.65 ± 1.42 GAE mg/g, and 4.77 ± 0.01 CE mg/g, respectively. The phenolic content increased as the heating time increased, as shown by the 180 min heating treatment (T180; 27.99 ± 0.38 GAE mg/g), but changes in total flavonoid content were not significant between different heating time treatments. Increasing the heating time of orange peels could improve the antioxidative activities (1,1-Diphenyl-2-picrylhydrazyl radical scavenging effect, ABTS+· scavenging effect and reducing power) of methanol peel extracts, but there were no significant difference between the β-carotene bleaching inhibition of the different heating time extracts, excluding T30. According to correlation analysis, one possible factor of increasing antioxidative activities was the production of phenolic compounds during heating treatment.
