Therefore, it might be an efficient means for brewers to increase total phenolic content during brewing for improvement in flavour stability of the final beer.

Significant positive correlations between wort fermentability and the assimilation of Lys and His under normal-gravity and high-gravity conditions indicated that Lys and His were the key amino acids for lager yeast during beer brewing. In order to obtain insight into the roles of Lys and His in nitrogen regulation, the influences of Lys, His and their mixture supplementations on the fermentation performance and nitrogen metabolism in lager yeast during high-gravity fermentation were further investigated in the present study. Results showed that Lys and His supplementations improved yeast growth, wort fermentability, ethanol yield and the formation of flavor volatiles. Lys supplementation up-regulated Ssy1p-Ptr3p-Ssy5p (SPS)-regulated genes (LYP1, HIP1, BAP2 and AGP1) dramatically compared to nitrogen catabolite repression (NCR)-sensitive genes (GAP1 and MEP2), whereas His supplementation activated SPS-regulated genes slightly in exponential phase, and repressed NCR-sensitive genes significantly throughout the fermentation. Lys and His supplementations increased the consumption of Glu and Phe, and decreased the consumption of Ser, Trp and Arg. Moreover, Lys and His supplementations exhibited similar effects on the fermentation performance, and were more effective than their mixture supplementation when the same dose was kept. These results demonstrate that both Lys and His are important amino acids for yeast nitrogen metabolism and fermentation performance.

This is the first report on the ability of soy sauce to effectively reduce the serum uric acid levels and xanthine oxidase (XOD) activities of hyperuricemic rats. Soy sauce was partitioned sequentially into ethyl acetate and water fractions. The ethyl acetate fraction with strong XOD inhibition effect was purified further. On the basis of xanthine oxidase inhibitory (XOI) activity-guided purification, nine compounds including 3,4-dihydroxy ethyl cinnamate, diisobutyl terephthalate, harman, daidzein, flazin, catechol, thymine, genistein, and uracil were obtained. It was the first time that 3,4-dihydroxy ethyl cinnamate and diisobutyl terephthalate had been identified from soy sauce. Flazin with hydroxymethyl furan ketone group at C-1 and carboxyl at C-3 exhibited the strongest XOI activity (IC50 = 0.51 ± 0.05 mM). According to fluorescence quenching and molecular docking experiments, flazin could enter into the catalytic center of XOD to interact with Lys1045, Gln1194, and Arg912 mainly by hydrophobic forces and hydrogen bonds. Flazin, catechol, and genistein not only were potent XOD inhibitors but also held certain antioxidant activities. According to ADME (absorption, distribution, metabolism, and excretion) simulation in silico, flazin had good oral bioavailability in vivo.

Summary Five commercial lager beers were used to investigate the evolution of antioxidant activity and ageing compounds during storage. The relationships between antioxidant activity and ageing compounds were clarified by principal component analysis (PCA). Results showed that total phenolic content (TPC) and antioxidant activities of beers evaluated by different assays gradually decreased by 16.08–22.71% (average of 18.56%) and 1.99–78.79% (averages of 24.44–70.50%), which was accompanied by 100.50–269.35% (average of 178.77%) and 11.11–57.14% (average of 28.73%) of increases in total ageing compounds and thiobarbituric acid (TBA) value, respectively, during 6 months of storage at 25 °C. Results from PCA elucidated that there were negative correlations between antioxidant activities and ageing compounds of beers during storage, and satisfactory discrimination among beers with different storage time could be achieved on the basis of antioxidant activities and typical ageing compounds selected.

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