Changes in chemical composition and antioxidant activity of dried Citrus unshiu peel after roasting

The aim of this study was to investigate the relationship between the chemical composition and antioxidant activity of roasted jinpi extract (RJE) under various roasting conditions (e.g., 100–155 °C). The total phenolic contents, flavonoid content, and antioxidant activities in RJE increased with increased roasting temperature, and the highest efficacy was observed at 155 °C. The narirutin and hesperidin contents in RJE reached 15.32 and 11.50 mg/g, respectively, under this optimal temperature (155 °C). The roasting process caused the Maillard reaction to occur which increased the amounts of 2,4-diamino-5-(3′,4′-dichlorophenyl)-6-methyl pyrimidine (DDMP) and 5-hydroxymethlyfurfural (5-HMF) but decreased the total sugar content in RJE. Among the compounds contained in RJE, DDMP had the strongest diethylene glycol, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, which was determined by DPPH-HPLC analysis. These results suggest that roasting jinpi under optimal conditions increases the amount of phenolics and flavonoids and thereby enhances the antioxidant activity of jinpi.