Effect of photoperiod on polyphenol biosynthesis and cellular antioxidant capacity in mung bean (Vigna radiata) sprouts

This study investigated the effects of photoperiods on the metabolic regulation of polyphenol biosynthesis, as well as antioxidant activities in mung bean sprouts. Mung bean sprouts exposed to three different photoperiods: constant dark (light/dark, 0/24 h), semilight (light/dark, 12/12 h) and constant light (light/dark, 24/0 h). The results showed that the DFR, F6H, F3'5'H, F3'H, and F3H genes in the polyphenol biosynthetic pathway, as well as PHOT1/2, HY5, and MYBs, were strongly stimulated by photoperiods in sprouts. Seven polyphenol compounds (caffeic acid, rutin, vitexin, daidzin, glycitin, ferulic acid and p-coumaric acid) were detected in sprouts; the first five gradually increased with increasing illumination time, especially rutin, which showed a 547% increase. Illumination enhanced the antioxidant activities of sprouts, which was potentially related to the increases in caffeic acid, rutin and vitexin. These findings indicated that illumination would be a promising technique to improve the nutritional value of mung bean sprouts.