Optimization of γ-Aminobutyric Acid (GABA) Accumulation in Germinating Adzuki Beans (Vigna angularis) by Vacuum Treatment and Monosodium Glutamate, and the Molecular Mechanisms

Abstract

This study aimed to investigate the optimal hypoxic and monosodium glutamate (MSG) stress conditions for the enrichment of γ-Aminobutyric acid (GABA) in germinating adzuki beans and to reveal the potential underlying molecular mechanisms of GABA accumulation. Using single-factor experiments and response surface model, we investigated the effects of germination time, germination temperature, vacuum time, and MSG concentration on GABA contents, and further explored the activity and gene expression of glutamate decarboxylase (GAD) and polyamine oxidase (PAO) critical rate restriction enzymes during GABA synthesis. The optimal soaking temperature, soaking time, and pH conditions were 35°C, 16 h, and 5, respectively. Furthermore, the optimal germination conditions for optimal GABA enrichment were 48 h, 1.99 mg/ml MSG concentration, germination temperature of 31.49°C, and vacuum time of 15.83 h. Under such conditions, the predicted GABA concentration was 443.57 ± 7.18 mg/100 g, with no significant difference between the predicted and experimental data. The vacuum + MSG (FZM) treatment has a maximum contribution rate of GABA to 38.29%, which significantly increase GABA content, and the increase was associated with increased GAD and PAO activity. In addition, MSG in combination with vacuum treatment could significantly induce VaGAD4 and VaGAD6 genes in 2 days germination of adzuki beans. According to the results of the present study, vacuum + MSG treatment is an effective approach to enhancing GABA accumulation in germinating adzuki beans, which could be employed in enhancing the functional quality of germinating adzuki beans.

Revealing the Hypoglycemic Effects and Mechanism of GABA-Rich Germinated Adzuki Beans on T2DM Mice by Untargeted Serum Metabolomics

“…In our previous paper ( 23 ), we described how to achieve GABA enrichment in sprouted adzuki beans with our new optimized method of germination by vacuum and monosodium Glu treatment. The present study focused on the anti-diabetic activity of GABA-enriched germinated adzuki beans.…”

“…The GABA content in the germinated adzuki beans was determined using the high-performance liquid chromatography (HPLC) (Agilent 1200, USA) system ( 11 ). The process optimization of GABA enrichment via germination and GABA content determination of germinated adzuki beans were reported in our latest article ( 23 ).…”

The Effects of GABA-Rich Adzuki Beans on Glycolipid Metabolism, as Well as Intestinal Flora, in Type 2 Diabetic Mice

“…Furthermore, the optimal germination conditions for optimal GABA enrichment were 48 h, 1.99 mg/ml MSG concentration, 31.49°C germination temperature, and 15.83 h vacuum time. The germinated adzuki beans were then divided into two parts: one was freeze-dried and used to measure GABA levels (our recent article ( 13 ) reported the preparation process of germinated adzuki beans and the optimization of GABA content) and subsequent animal experiments.…”

“…Adzuki bean contains a high amount of sodium glutamate (MSG), which is a good source of GABA, an earlier study has shown that germination treatment can increase GABA content in the bean ( 13 ), and dietary supplementation with GABA or GABA-rich foods is a common strategy for the treatment of T2DM. GABA-rich brown rice improves the blood glucose level of rats with T2DM ( 14 ) and has protective effects against liver and pancreatic injury ( 15 ).…”

From plant biology research to technology transfer and knowledge extension: improving food quality and mitigating environmental impacts

“…Based on earlier reviews of the literature, it was first suggested that arginine, derived from the mobilization of protein reserves in germinating seeds, is degraded to urea and ornithine, with the carbon and nitrogen from ornithine being converted via Glu to GABA, and then reported that GABA synthesis can be elevated by environmental stimulii Shelp 1989, 1997). As might be predicted from the biochemical properties of the plant GAD, an acidic pH of 5-6, a temperature of approximately 30-40 °C, and the addition of exogenous Glu and Ca 2+ /CaM are optimal for generating GABA in sprouting grain and germinating seeds (Scott-Taggart et al 1999;Oh 2003;Chung et al 2009;Techo et al 2018;Jiang et al 2021). Hypoxia also increases the GABA level (Chung et al 2009;Lin et al 2015;Shen et al 2015;Thuwapanichayanan et al 2015;Ding et al 2016;Techo et al 2018).…”