Effect of acid pretreatment and the germination period on the composition and antioxidant activity of rice bean (Vigna umbellata)

•Germination increases crude protein and total phenolic content of rice bean.•Acid pretreatment and germination improve antioxidant activities of rice bean.•Germination strongly affects an increase in alanine, glutamic acid and serine.•Acid pretreatment leads to a significant decrease in intensity of the 76 kDa band.•Ethanolic extract contains more phenolics and antioxidant than water extract.

This research evaluated effect of germination period and acid pretreatment on chemical composition and antioxidant activity of rice bean sprouts. Moisture, total phenolics, reducing sugar and B vitamins (thiamine, riboflavin, and niacin) content of steamed sprouts increased with increasing germination time (p ⩽ 0.05). Pretreatment with 1% (w/v) citric acid for 6 h significantly increased the total phenolic content. The 18-h-germinated rice beans showed the highest crude protein content, as determined using the Kjeldahl method. During germination, acid pretreatment led to a significant decrease in the intensity of the 76-kDa band. Germination caused a significant increase in radical scavenging activity and ferric reducing antioxidant power, especially in sprouts from citric acid-treated seeds. The antioxidant activities of the ethanolic extracts from both pretreated beans and the control were 1.3-1.6 times higher than those obtained from the water extracts. Major phenolics found in both 0-h and 18-h-germinated rice beans were catechin and rutin.