Accumulation of γ-aminobutyric acid in soybean by hypoxia germination and freeze-thawing incubation

Novel strategy to raise the content of aglycone isoflavones in soymilk and gel: Effect of germination on the physicochemical properties

Germination holds the key to nutritional equilibrium in plant grains. In this study, the effect of soybean germination on the processing of soymilk (SM) and glucono-δ-lactone (GDL) induced soymilk gel (SG) was investigated. Germination promoted soybean sprout (SS) growth by activating the energy metabolism system. The energy metabolism was high during the three-day germination and was the most vigorous on the second day of germination. After germination, protein dissolution was improved in SM, and endogenous enzymes produced small molecule proteins. Small molecule proteins were more likely to aggregate to produce SM protein particles. Germination increased the water-holding capacity of SG induced by GDL but weakened the strength. Furthermore, the dynamic fluctuations in isoflavone content were closely monitored throughout the processing of soybean products, including SS, SM, and SG. Although the total amount of isoflavones in SM and SG processed from germinated soybeans decreased, a significant enrichment in the content of aglycone isoflavones was observed. The content of aglycone isoflavones in SG processed from germinated soybeans on the second day of germination was 736.17 ± 28.49 µg/g DW, which was 83.19 % higher than that of the control group. This study demonstrates that germination can enhance the nutritional value of soybean products, providing innovative opportunities for the development of health-promoting soybean-based products.

Production and quality evaluation of a novel γ-aminobutyric acid-enriched yogurt

Objective

γ-aminobutyric acid (GABA) is a neurotransmitter inhibitor that has beneficial effects on various health conditions such as hypertension, cognitive dysfunction, and anxiety. In this study, we investigated a novel yogurt naturally enriched with GABA using a Levilactobacillus brevis strain isolated in our laboratory; the specific optimum yogurt production conditions for this strain were determined.

Methods

We isolated an L. brevis strain and used it to produce yogurt naturally enriched with GABA. We explored the optimal conditions to enhance GABA yield, including fermentation temperature, inoculation amount, L-monosodium glutamate (L-MSG) concentration, fermentation time, and sucrose content. We also performed mixed fermentation with Streptococcus thermophilus and evaluated the quality of the yogurt.

Results

Following optimization (43°C, 8% inoculation amount, 1.5 g/L L-MSG, and 8% sucrose for 40 h of fermentation), the GABA yield of the yogurt increased by 2.2 times, reaching 75.3 mg/100 g. Mixed fermentation with S. thermophilus demonstrated favorable results, achieving a GABA yield akin to that found in some commercially available functional foods. Moreover, the viable microbe count in the GABA-enriched yogurt exceeded 1 × 108 cfu/mL, which is higher than that of commercial standards. The yogurt also exhibited a suitable water-holding capacity, viscosity, 3-week storage time, and favorable sensory test results.

Conclusion

This study highlights the potential of naturally enriched GABA yogurt as a competitive commercial yogurt with beneficial health effects.

Optimizing Levilactobacillus brevis NPS-QW 145 Fermentation for Gamma-Aminobutyric Acid (GABA) Production in Soybean Sprout Yogurt-like Product

Gamma-aminobutyric acid (GABA) is a non-protein amino acid with various physiological functions. Levilactobacillus brevis NPS-QW 145 strains active in GABA catabolism and anabolism can be used as a microbial platform for GABA production. Soybean sprouts can be treated as a fermentation substrate for making functional products. This study demonstrated the benefits of using soybean sprouts as a medium to produce GABA by Levilactobacillus brevis NPS-QW 145 when monosodium glutamate (MSG) is the substrate. Based on this method, a GABA yield of up to 2.302 g L^-1 was obtained with a soybean germination time of one day and fermentation of 48 h with bacteria using 10 g L^-1 glucose according to the response surface methodology. Research revealed a powerful technique for producing GABA by fermentation with Levilactobacillus brevis NPS-QW 145 in foods and is expected to be widely used as a nutritional supplement for consumers.

Enhancement of γ-aminobutyric acid content in shells of passion fruit (Passiflora edulis) under anoxic vacuum conditions

Passiflora edulis, commonly known as passion fruit, is a popular all-weather fruit eaten fresh or processed. Its shells, which currently are mostly discarded as waste and hurt the environment, account for more than half of the passion fruit. The shells contain gamma-aminobutyric acid (GABA) which is the main inhibitory neurotransmitter and has many proven medical values such as antidepressant, anti-anxiety, etc. Many studies have shown that GABA production in plants can be significantly increased by reverse stress. Taking Tainong 1 as a typical passion fruit cultivar, this study explored the optimal anoxic vacuum treatment for increasing the GABA content of passion fruit shells. The content increased to 2139.25 ± 26.69 mg/100 g on day 4 of chill storage after vacuum packing (63.68% higher than the control). The activities of glutamate decarboxylase (GAD) and diamine oxidase (DAO) were significantly higher in the vacuum-treated group than in the control group after 4 days of vacuum-chill storage. On day 5 of vacuum-chill storage, the activities of all measured enzymes decreased except for the increase of GABA transaminase (GABA-T), which was accompanied by a decrease in GABA content. Vacuum treatment and subsequent chill storage increased the content of GABA, thereby increasing functional value of passion fruit shells.

Mass spectrometry imaging enables visualization of the localization of glutamate decarboxylase activity in germinating legume seeds

Visualizing the distribution of enzymes is vital for understanding physiological phenomena. Enzyme histochemistry is a technique used to investigate the localization of enzyme activity. However, the target is restricted to enzymes with easy-to-design artificial substrates that can develop color through reactions. Mass spectrometry imaging (MSI)-based enzyme histochemistry has been developed as a novel method to visualize enzyme localization. It can be applied to enzyme histochemistry as it detects products from the supplied substrate using enzymes present on the tissue sections. However, enzyme histochemistry using MSI has not been applied to plant tissue samples yet. Glutamate decarboxylase (GAD, EC: 4.1.1.15) is an enzyme that catalyzes the decarboxylation reaction of l-glutamic acid to produce γ-aminobutyric acid (GABA). GABA biosynthesis is important both in the field of food chemistry and plant physiology. This study focused on GAD during the legume germination process and successfully visualized GAD activity in legume seeds using MSI for the first time. Furthermore, the localization of GAD activity in the embryonic axis of germinated soybean seeds and alfalfa seeds could be visualized.

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

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.

The versatile GABA in plants

Gamma-aminobutyric acid (GABA) is a ubiquitous four-carbon, non-protein amino acid. GABA has been widely studied in animal central nervous systems, where it acts as an inhibitory neurotransmitter. In plants, it is metabolized through the GABA shunt pathway, a bypass of the tricarboxylic acid (TCA) cycle. Additionally, it can be synthesized through the polyamine metabolic pathway. GABA acts as a signal in Agrobacterium tumefaciens-mediated plant gene transformation and in plant development, especially in pollen tube elongation (to enter the ovule), root growth, fruit ripening, and seed germination. It is accumulated during plant responses to environmental stresses and pathogen and insect attacks. A high concentration of GABA elevates plant stress tolerance by improving photosynthesis, inhibiting reactive oxygen species (ROS) generation, activating antioxidant enzymes, and regulating stomatal opening in drought stress. The transporters of GABA in plants are reviewed in this work. We summarize the recent research on GABA function and transporters with the goal of providing a review of GABA in plants.

Accumulation of Agmatine, Spermidine, and Spermine in Sprouts and Microgreens of Alfalfa, Fenugreek, Lentil, and Daikon Radish

Sprouts and microgreens are a rich source of various bioactive compounds. Seeds of lentil, fenugreek, alfalfa, and daikon radish seeds were germinated and the contents of the polyamines agmatine (AGM), putrescine (PUT), cadaverine (CAD), spermidine (SPD), and spermine (SPM) in ungerminated seeds, sprouts, and microgreens were determined. In general, sprouting led to the accumulation of the total polyamine content. The highest levels of AGM (5392 mg/kg) were found in alfalfa microgreens, PUT (1079 mg/kg) and CAD (3563 mg/kg) in fenugreek sprouts, SPD (579 mg/kg) in lentil microgreens, and SPM (922 mg/kg) in fenugreek microgreens. A large increase in CAD content was observed in all three legume sprouts. Conversely, the nutritionally beneficial polyamines AGM, SPD, and SPM were accumulated in microgreens, while their contents of CAD were significantly lower. In contrast, daikon radish sprouts exhibited a nutritionally better profile of polyamines than the microgreens. Freezing and thawing of legume sprouts resulted in significant degradation of CAD, PUT, and AGM by endogenous diamine oxidases. The enzymatic potential of fenugreek sprouts can be used to degrade exogenous PUT, CAD, and tyramine at pH values above 5.

Exogenous Spermidine Promotes γ-Aminobutyric Acid Accumulation and Alleviates the Negative Effect of NaCl Stress in Germinating Soybean (Glycine max L.)

We investigated the effects of exogenous spermidine (Spd) on the physiological status, γ-aminobutyric acid (GABA) synthase activity, and gene expressions in germinating soybeans under NaCl stress. The results show that Spd significantly increases sprout growth and biomass, decreases malonaldehyde and H2O2 contents, and markedly promotes the activities of superoxide dismutase, catalase, peroxidase, and glutathione peroxidase of germinating soybeans. The harmful effect of NaCl stress was alleviated by exogenous Spd. GABA accumulation in germinating soybeans was caused by the activation of diamine oxidase, polyamine oxidase, aminoaldehyde dehydrogenase, and glutamate decarboxylase activities and by up-regulating their gene expression under Spd-NaCl treatment. The GABA content decreased by 57% and 46% in germinating soybeans with the application of aminoguanidine under Spd and Spd-NaCl treatments, respectively. In conclusion, spermidine induces the accumulation of GABA and increases sprouts biomass, thereby enhancing the functional quality of germinating soybeans.

The mechanism of freeze-thawing induced accumulation of γ-aminobutyric acid in germinated soybean

BACKGROUND

γ-Aminobutyric acid (GABA) is a non-protein amino acid with several functions in the human body. Although freeze-thawing could effectively accumulate GABA in soybean sprouts, the mechanism has not been revealed. The mechanism by which freeze-thawing enhances GABA accumulation in germinated soybean was revealed by evaluating GABA content, the activity of related synthesis enzymes, and the microstructure of the tissues and cells of sprouts. The germinated soybeans were treated at different temperatures (from -196 °C to 25 °C) for 12 h and then thawed at 25 °C for 6 h.

RESULTS

The results showed that GABA content in frozen soybean sprouts did not change significantly before thawing. After thawing, the GABA content of sprouts increased by 83.9% and 82.9% when treated by liquid nitrogen flash freeze at - 80 °C for 12 h compared with the control (4 °C treatment for 12 h). The results indicated that GABA formation mainly occurred during thawing. However, glutamate decarboxylase (GAD), diamine oxidase (DAO), and aminoaldehyde dehydrogenase (AMADH) activity decreased during thawing. Based on the malonaldehyde (MDA) content and microstructure of sprouts, it was suggested that freezing at lower temperatures (< -20 °C) maintained the integrity of the cell structure, while the tissues and cell membranes were broken during thawing.

CONCLUSION

These results could provide evidence for the hypothesis that GABA formation resulted from full contact between enzymes and substrates during thawing, rather than the contribution of higher enzyme activity. © 2019 Society of Chemical Industry.

AMADH inhibitor optimization and its effects on GABA accumulation in soybean sprouts under NaCl-CaCl2 treatment

ABSTRACT

1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide (EDC) was the suitable inhibitor for aminoaldehyde dehydrogenase (AMADH) compared with N-ethylmaleimide (NEE) and iodoacetamide (IAM). EDC exhibited the most obvious inhibition effect on AMADH activity, while its inhibition on glutamate decarboxylase (GAD) was insignificant. Compared with the control, AMADH activity reduced by 70.4% with 0.5 mM EDC, and γ-aminobutyric acid (GABA) content declined by 44.3% in soybean sprouts at 4 days of germination. AMADH activity reduced by 80.62, 67.61 and 72.02% in the 4-day sprouts with 1 mM EDC under NaCl, CaCl2 and NaCl + CaCl2 treatment, respectively, and GABA content decreased by 43.56, 38.84 and 35.53%, respectively. EDC is a proper inhibitor for AMADH and it could be used to quantify the contribution of polyamine degradation pathway on GABA formation. In soybean sprouts, the presence of CaCl2 under NaCl stress decreased the contribution of polyamine degradation pathway on GABA accumulation.

GRAPHICAL ABSTRACT

Roles of oxides of nitrogen on quality enhancement of soybean sprout during hydroponic production using plasma discharged water recycling technology

This study was performed to assess the effect of plasma-discharged water recycling technology as irrigation water on soybean sprout production. Two different types of irrigation water were used individually for cultivation, including plasma discharged water as a source of oxides of nitrogen and tap water, irrigation water was recycled for every 30 minutes. Plasma discharged irrigation water reduced overall 4.3 log CFU/ml aerobic microbe and 7.0 log CFU/ml of artificially inoculated S. Typhimurium within 5 minutes and 2 minutes, respectively, therefore sprout production occurs in a hygienic environment. Using of plasma-discharged water for cultivation, increases the amount of ascorbate, asparagine, and γ-aminobutyric acid (GABA) significantly (p < 0.05), in the part of cotyledon and hypocotyl of soybean sprout during 1 to 4 days of farming. A NO scavenger, 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (cPTIO), was added in irrigation water to elucidate the roles of the oxides of nitrogen such as NO3-, NO2- generated in plasma discharged water. It was observed that all three nutrients decreased in the cotyledon part, whereas ascorbate and GABA contents increased in the hypocotyl and radicle part of bean sprout for the same duration of farming. The addition of NO scavenger in the irrigation water also reduced growth and overall yield of the soybean sprouts. A recycling water system with plasma-discharged water helped to reduce the amount of water consumption and allowed soybean sprouts growth in a hygienic environment during the hydroponic production.

γ-Aminobutyric Acid (GABA) Accumulation in Tea (Camellia sinensis L.) through the GABA Shunt and Polyamine Degradation Pathways under Anoxia

γ-Aminobutyric acid (GABA) is an important bioactive component of tea (Camellia sinensis) providing various health benefits. We studied GABA accumulation via the GABA shunt and polyamine degradation pathways under anoxia in tea leaves. Anoxia caused a ∼20-fold increment in GABA concentration, relative to fresh tea leaves. This increment was due to the increase of glutamate decarboxylase and diamine oxidase activities. Genes involved in GABA formation, such as CsGAD1 and CsGAD2, were significantly up-regulated by anoxia. The concentrations of putrescine and spermine, two substrates for GABA production, were also increased by anoxia. Treating tea leaves with aminoguanidine completely inhibited diamine oxidase activity during anoxia, but the concentration of GABA decreased by only ∼25%. We infer that about one-fourth of GABA formed in tea leaves under anoxia comes from the polyamine degradation pathway, opening the possibility of producing GABA tea based through the regulation of metabolism.