Mechanism of γ-aminobutyric acid production from the enzymatic hydrolysis of urea-solubilized glutenin by mung bean sprout juice

Abstract

γ-aminobutyric acid (GABA) has been recognized for its pivotal role in inhibiting neural excitability and is used considerably in foods and pharmaceuticals. Synthetic GABA may result in significant adverse effects, such as drowsiness and dizziness. In contrast, natural GABA supplementation is associated with minimal side effects. In this paper, GABA was prepared by hydrolyzing gluten fractions using multiple enzymes in bean sprout juice. After enzymatic hydrolysis with mung bean sprout juice, the order of GABA content in the gluten fractions was as follows: urea-soluble glutenin (USG) > αβγ-gliadin > ω-gliadin > alkali-soluble glutenin (ASG). The highest GABA content (2.72 mg/g) was achieved by hydrolyzing USG with 2 % bean sprout juice at 40 °C for 8 h. The maximum UV absorbance of mung bean sprout juice was close to that of ASG. The α-helical structure of USG with a higher content of disulfide bonds, corresponding to an X-ray diffraction angle of 22.2°, disappeared after hydrolysis. The exposure of isoleucine in USG possibly enhances the structural stability of succinic semi-aldehyde dehydrogenase. After hydrolysis, C_γ of phenylalanine and histidine from USG were present. The substrates for converting GABA in USG, along with the precursors catalyzing glutamate decarboxylase, GABA transaminase, and succinate dehydrogenase, were denoted as Q5D862, P10387, Q10464, and P02863 by label-free quantification (LFQ), respectively. A novel, cost-effective, and eco-friendly method to produce GABA was developed, and the application fields of USG would be broadened.