Antioxidant properties of some Sri Lankan traditional red rice (Oryza sativa L.)

Abstract

Abstract Rice bran is one of the most abundant co-products produced in the rice milling industry and research conducted in last two decades has shown that it contains a unique complex of naturally occurring antioxidant compounds. Rice is the staple food in Sri Lanka and there are over 300 different traditional Sri Lankan rice varieties (RV). However, no antioxidant activity evaluation study has been conducted on these indigenous varieties. Present study evaluates the antioxidant properties of some Sri Lankan traditional red RV. Freeze-dried 70% ethanolic extracts of brans of 4 traditional red RV (Oryza sativa) namely Masuran (M), Dik Wee (DW), Goda Heeneti (GH) and Sudu Heeneti (SH) were used in this study. Antioxidant properties of bran extracts of selected RV were evaluated using total polyphenolic content (TPC) (n=6), 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging (n=4), 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid [ABTS] radical scavenging (n=4) and ferric reducing antioxidant power (FRAP) (n=6) in vitro antioxidant assays. Significant differences were observed among bran extracts of selected RV for investigated antioxidant properties (P<0.05). Mean TPC, DPPH, ABTS and FRAP antioxidant properties were in the range of 11.74 - 29.75 mg gallic acid equivalents/g, 5.14 ± 0.17 - 6.77 ± 0.06 mmol Trolox equivalents (TE)/100g, 8.67 ± 0.14 - 14.25 ± 0.46 mmol TE/100g, 8.30 ± 0.15 - 11.02 ± 0.25 mmol FeSO4/100 g rice bran respectively. The order of mean TPC was SH > M > GH > DW. Bran extracts of all the RV exhibited dose dependent radical scavenging activity against both DPPH· and ABTS radicals. Bran extracts of GH demonstrated maximum radical scavenging activity for both radicals. However, the order of scavenging was observed to be different among bran extracts of different RV for DPPH· and ABTS radicals. The order of scavenging for DPPH· was GH > SH > DW > M and for ABTS it was observed as GH > SH > M > DW. Highest mean 290 FRAP was observed for bran extract of GH variety while lowest for bran extract for SH variety. The antioxidant power of the bran extracts for FRAP was in the order of GH > M > DW > SH