Profiling polyphenol composition and antioxidant activity in Australian-grown rice using UHPLC Online-ABTS system

The aim of this study was to profile the polyphenol composition and antioxidant activity of 8 Australian-grown rice varieties. UHPLC with an online ABTS system was used to identify and quantify individual polyphenols present in the rice extract whilst simultaneously measuring their respective antioxidant activity. In addition, the synergistic antioxidant activity of the rice extracts was assessed using the ferric reducing ability of plasma assay (FRAP). The study found that the pigmented rice varieties had higher total antioxidant activity than the brown non-pigmented rice varieties. The red variety Yunlu29 had the highest FRAP total antioxidant activity (303.8 ± 16.16 mg 100 g−1 Trolox equivalents). UHPLC profile of Yunlu29 revealed a wide variety of active polyphenols. In particular, the chromatogram from the red rice variety Yunlu29, contained two unidentified peaks that exhibited the highest antioxidant activity. In the purple rice extract, cyanidin-3-glucoside and peonidin-3-glucoside were profiled as having the most free-radical scavenging activity. In comparison, the brown non-pigmented rice extracts did not exhibit substantial antioxidant activity in its polyphenol UHPLC profile. The results of this study demonstrate the antioxidant potential of polyphenols present in Australian-grown pigmented and non-pigmented rice varieties which may have a future role as a potential functional food ingredient.