Accumulation of γ-aminobutyric acid and modifications of phenolic profiles and antioxidant capacity of foxtail millets during germination

This study investigated the influence of sprouting on the gamma-aminobutyric acid (GABA) concentration, phenolic composition, and antioxidant activity of foxtail millets. Phenolic compounds and GABA were significantly enriched during the sprouting process, with an increase of 4.25-5.59 fold and 18.56%-36.40%, respectively, after germination for three days. However, the total flavonoid content (TFC) was only significantly increased (p < 0.05) in one cultivar (JS-1). A total of 25 compounds were identified in the free phenolic extracts, with 3-p-coumaroylquinic acid, N-feruloylserotonin and N-(p-coumaroyl) serotonin appearing after sprouting for two days. The main polyphenols in the free fraction, feruloylquinic acid and trans-ferulic acid, increased by 95.78% and 11.95%, respectively after three days of germination. Trans-p-coumaric and trans-ferulic acid, the two principal phenolic compounds in the bound fractions, increased by 23.28% and 46.38%, respectively. The sprouted foxtail millets showed a significantly higher in vitro antioxidant activity than their corresponding un-germinated grains (p < 0.05). Our results suggest that sprouted foxtail millet can be exploited as a functional food product enriched in GABA and enhanced in natural antioxidants.