Biochemical processes, chemical compositions, and nutrient profiles of germinated barley grains after steeping with thiolated and aminated spent brewer's yeast hydrolysates

The present study investigated the effect of steeping solution containing a thiol- and amino-functionalization of hydrolyzed brewers' spent yeast hydrolysate (HBSY) on the enzymatic and nutritional profile of germinated barley. Thiol- and amino-functionalized HBSY (GSN) resulted in significantly elevated activities of α-amylase (35.5 U/g), β-amylase (41.2 U/g), protease (29.9 U/g), cysteine protease (12.6 U/g), lipase (4.8 U/g), and phytase (3.4 U/g) compared to control samples germinated in water (GW) (α-amylase: 23.5 U/g; β-amylase: 12.4 U/g; protease: 8.4 U/g; cysteine protease: 2.6 U/g; lipase: 2.1 U/g; phytase: 1.06 U/g). Higher cysteine protease activity was associated with increased β-amylase activity, consistent with a higher maltose concentration in GSN (2.92 g/L) than in the control (1.81 g/L). Comparative electrophoretic patterns and the branch-chain length distribution of amylopectin indicated that GSN is reflected more strongly in protease- and amylase-mediated hydrolysis, respectively. Steeping with GSN during a 96-h germination period produced nearly twice the γ-aminobutyric acid (GABA) content (2381.30 μg/g) compared with water steeping (1132.00 μg/g). Fortification with GSN resulted in significantly elevated levels of folic acid, niacin, riboflavin, γ-tocopherol, and minerals.