Antioxidant potential of selected whole grain cereals consumed by Sri Lankans: a comparative in vitro study

Whole grains of rice [improved: Bw 361 (red) and Bg 359 (white); traditional: Kalu Heeneti (red) and Suwadal (white)], corn, finger millet, wheat, barley and oat were used in this study. Ethanolic extracts (EEs) and methanolic extracts (MEs) of whole grain cereals were evaluated for total polyphenolic content (TPC), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), DPPH and ABTS radical scavenging antioxidant properties (AP) in vitro (n=3 each). Results showed significant differences (p<0.05) between extracts and among cereals for investigated AP. In general, MEs of cereals showed significantly higher (p<0.05) activity compared to EEs of cereals. Among the studied cereals, finger millet exhibited the highest AP in both extracts for TPC, FRAP and ORAC while for DPPH and ABTS it's only in MEs. The mean TPC, FRAP and ORAC of MEs of finger millet were 708.45 ± 11.72 mg gallic acid equivalents (GAE), 1413.69 ± 1.61, 1240.45 ± 67.38 mg Trolox equivalents (TE) and 955.76 ± 2.03 mg TE/100 g grain, respectively while for EEs it was 275.36 ± 4.26 mg GAE, 606.34 ± 5.00 mg TE and 1112.52 ± 24.38 TE/100 g grain respectively. For DPPH and ABTS radical scavenging activities the IC50 values of MEs of finger millet were 49.42 ± 6.65 and 10.74 ± 0.44 μg/mL respectively. Of the cereals analyzed the second highest AP was observed in traditional red rice variety, Kalu Heeneti (except for ORAC) for both extracts tested. Whole grains of wheat and oats had very low AP compared to finger millet and red rice varieties analyzed in the present study. It is concluded that finger millet possesses highest AP.