On-line high-performance liquid chromatography analysis of the antioxidant activity of phenolic compounds in selected tropical citrus

Citrus hystrix, Citrus microcarpa and Citrus suhuiensis fruits were analysed by high-performance liquid chromatography (HPLC) with photo-diode array and MS2 detector (HPLC-PDA-MS2) to identify flavone, flavanone and dihydrochalcone. The antioxidant potential on each tropical citrus flavonoid was performed using HPLC with post-column on-line antioxidant detection based on 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging assay. Phloretin-3′,5′-di-C-glucopyranoside present in C. microcarpa fruit peel and flesh possess high Trolox Equivalent Antioxidant Ratio (TEAR) values by 3.4 and 3.1 respectively. Quercetin-3-O-rutinoside, hesperetin-7-Oneohesperidoside and hesperetin-7-O-rutinoside also showed high TEAR values in C. hystrix and C. suhuiensis fruit, but have lower than phloretin-3′,5′-di-C-glucopyranoside. Levels of TEAR values of flavonoids in C. microcarpa, C. suhuiensis and C. hystrix fruits were as follows; phloretin-3′,5′-di-Cglucopyranoside quercetin-3-O-rutinoside hesperetin-7-O-neohesperidoside hesperetin-7-O-rutinoside = luteolin-7-O-rutinoside = naringenin-7-Orutinoside. Citrus microcarpa has been widely used in Asian food and beverages or as a preserved snack, is consider to be a good source of phloretin-33′,5′-di-Cglucopyranoside. This compound is structurally almost similar to aspalathin and nothofagin, the potent antioxidant compounds in rooibos tea.