Abstract: During seed germination, γ-aminobutyric acid (GABA) and phenolics are both accumulated, and GABA may play a regulatory role in the accumulation of phenolics. In this study, the effect of exogenous GABA at doses of 0, 2.5, 5, 10 and 20 mmol/L was investigated on the growth indices, total phenolics and phenolic acid contents and antioxidant capacity of germinated soybean grown in hydroponics. The results showed that 2.5, 5 mmol/L exogenous GABA could significantly increase the sprout length, mass, growth (P < 0.05). With the increase in GABA concentration, the contents of total phenolics and free phenolic acid increased gradually. When the concentration of GABA was 20 mmol/L, the content of total phenolics was enhanced by 1.39 times relative to the control group. However, the content of bounded phenolic acid increased firstly and then decreased with the increase in GABA concentration, reaching the highest value at 2.5 mmol/L concentration, proving that bound phenolic acid was released gradually and transformed into a free form. In addition, GABA treatment also improved the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl, 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) cation radical and the activities of peroxidase, catalase and ascorbic acid peroxidase. The above findings indicated that exogenous GABA significantly promoted the growth of germinated soybean, regulated the activity of phenylalanine ammonia lyase, induced the accumulation of phenolics, and enhanced the activity of antioxidant enzymes as well as the free radical scavenging capacity in vitro, which will provide a theoretical basis for the development of soybean sprouts rich in phenolics.

Key words: γ-aminobutyric acid; total?phenolics; phenolic?acid; antioxidant capacity