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

Xiujie Jiang,Hongdou Jia,Xinting Shen,Jianbin Yuan,Aiwu Zhang,Yong Liu,Qingpeng Xu,Dongmei Cao,Liqin Zhao,Dongjie Zhang,Liwei Gu,Zhijiang Li

doi:10.3389/fnut.2021.693862

Xiujie Jiang, Hongdou Jia + Show 10 more

Open Access

https://doi.org/10.3389/fnut.2021.693862

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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.

Highlights

Γ-Aminobutyric acid (GABA) is a four-carbon nonproteinogenic amino acid that acts as a major inhibitory neurotransmitter in the central nervous system [1]
We investigated the effects of vacuum conditions and Monosodium glutamate (MSG) treatment on GABA contents in the germinating adzuki beans, in addition to the activity and expression of key enzymes (e.g., glutamate decarboxylase (GAD) and polyamine oxidase, PAO) in the GABA synthesis pathway
The optimal germination conditions were identified as a vacuum in combination with MSG treatment based on germination for 48 h, 1.99 mg/ml MSG concentration, and 41.49◦C germination temperature, and 15.83 h vacuum time, with a predicted GABA concentration of 443.57 ± 7.18 mg/100 g, which is 1.53 times the under normal germination, and 18.54 times higher than no germination

Summary

Introduction

Γ-Aminobutyric acid (GABA) is a four-carbon nonproteinogenic amino acid that acts as a major inhibitory neurotransmitter in the central nervous system [1]. The adzuki bean, which has been planted in China for more than 2,000 years, has high nutritional value and is a great source of protein, carbohydrates, vitamins, and minerals [13] It contains diverse amino acids, with a glutamic acid content of 3,608 mg/100 g [14]. We investigated the effects of vacuum conditions and MSG treatment on GABA contents in the germinating adzuki beans, in addition to the activity and expression of key enzymes (e.g., GAD and polyamine oxidase, PAO) in the GABA synthesis pathway. The present study aimed to reveal the contribution of exogenous MSG treatment under vacuum stress on GABA synthesis in germinating adzuki bean, and the underlying molecular mechanisms

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