Assessment of intra and inter species variation in antioxidant composition and activity in marginalized Fonio millet (Digitaria spp.)

摘要

Fonio (Digitaria spp.) is a highly nutritious, health promoting and cheaply available cereal which is, however, marginalized in many parts of Nigeria, and research attention on the crop is yet to measure up to its usefulness as a dietary staple. In this study therefore, five accessions each of two common species (Digitaria exilis and Digitaria iburua) were assessed for intra and inter- species variation in antioxidant activities. Total phenols were higher (p<0.05) in D. iburua than D. exilis accessions (0.64 to 1.59 and 0.43 to 0.63 mg gallic acid equivalents g-1 specimen, respectively). D. iburua accessions scavenged 50% of stable 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with greater potency (EC50 = 0.278 to 0.816 mg/mL) compared to D. exilis accessions (0.916 to 2.325 mg/ml). D. iburua accessions further showed higher (p<0.05) 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging potency (6.939 to 8.677 trolox equivalents) than D. exilis accessions (0.365 to 6.070 trolox equivalents). Total antioxidant capacity of D. iburua accessions ranged from 17.76 to 27.44 ascorbic acid equivalents, and was significantly higher (p<0.05) than those of D. exilis (8.69 to 15.80 ascorbic acid equivalents). Correlation analysis revealed that antioxidant activity of the fonio accessions was significantly associated with their total phenols content, but had little association with extract yields. Taken together, the study results provide evidence that fonio grains contain useful antioxidants, which varied significantly within and across species. Optimum antioxidant benefits in fonio would be derived more from D. iburua than D. exilis. However, environmental influence on antioxidant activity of the crop could also be prevalent, given the observed significant variation among accessions of both species.