In situ production of γ-aminobutyric acid in breakfast cereals

Microbial-Derived γ-Aminobutyric Acid: Synthesis, Purification, Physiological Function, and Applications

γ-Aminobutyric acid (GABA) is an important nonprotein amino acid that extensively exists in nature. At present, GABA is mainly obtained through chemical synthesis, plant enrichment, and microbial production, among which microbial production has received widespread attention due to its safety and environmental benefits. After using microbial fermentation to obtain GABA, it is necessary to be isolated and purified to ensure its quality and suitability for various industries such as food, agriculture, livestock, pharmaceutics, and others. This article provides a comprehensive review of the different sources of GABA, including its presence in nature and the synthesis methods. The factors affecting the production of microbial-derived GABA and its isolation and purification methods are further elucidated. Moreover, the main physiological functions of GABA and its application in different fields are also reviewed. By advancing our understanding of GABA, we can unlock its full potential and further utilize it in various fields to improve human health and well-being.

High Production of γ-Aminobutyric Acid by Activating the xyl Operon of Lactobacillus brevis

γ-Aminobutyric acid (GABA) is an inhibitory neurotransmitter with important physiological functions such as sleep assistance and anti-depression. In this study, we developed a fermentation process for the high-efficiency production of GABA by Lactobacillus brevis (Lb. brevis) CE701. First, xylose was found as the optimal carbon source that could improve the GABA production and OD₆₀₀ in shake flasks to 40.35 g/L and 8.64, respectively, which were 1.78-fold and 1.67-fold of the glucose. Subsequently, the analysis of the carbon source metabolic pathway indicated that xylose activated the expression of the xyl operon, and xylose metabolism produced more ATP and organic acids than glucose, which significantly promoted the growth and GABA production of Lb. brevis CE701. Then, an efficient GABA fermentation process was developed by optimizing the medium components using response surface methodology. Finally, the production of GABA reached 176.04 g/L in a 5 L fermenter, which was 336% higher than that in a shake flask. This work enables the efficient synthesis of GABA using xylose, which will provide guidance for the industrial production of GABA.

Creation and gene expression analysis of a giant embryo rice mutant with high GABA content

Gamma-amino butyric acid (GABA) is a natural non-protein amino acid involved in stress, signal transmission, carbon and nitrogen balance, and other physiological processes in plants. In the human body, GABA has the effects of lowering blood pressure, anti-aging, and activating the liver and kidneys. However, there are few studies on the molecular regulation mechanism of genes in the metabolic pathways of GABA during grain development of giant embryo rice with high GABA content. In this study, three glant embryo (ge) mutants of different embryo sizes were obtained by CRISPR/Cas9 knockout, and it was found that GABA, protein, crude fat, and various mineral contents of the ge mutants were significantly increased. RNA-seq and qRT-PCR analysis showed that in the GABA shunt and polyamine degradation pathways, the expression levels of most of the genes encoding enzymes promoting GABA accumulation were significantly upregulated in the ge-1 mutant, whereas, the expression levels of most of the genes encoding enzymes involved GABA degradation were significantly downregulated in the ge-1 mutant. This is most likely responsible for the significant increase in GABA content of the ge mutant. These results help reveal the molecular regulatory network of GABA metabolism in giant embryo rice and provide a theoretical basis for the study of its development mechanisms, which is conducive to the rapid cultivation of GABA-rich rice varieties, promoting human nutrition, and ensuring health.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01353-1.

Recent advances of γ-aminobutyric acid: Physiological and immunity function, enrichment, and metabolic pathway

γ-aminobutyric acid (GABA) is a non-protein amino acid which naturally and widely occurs in animals, plants, and microorganisms. As the chief inhibitory neurotransmitter in the central nervous system of mammals, it has become a popular dietary supplement and has promising application in food industry. The current article reviews the most recent literature regarding the physiological functions, preparation methods, enrichment methods, metabolic pathways, and applications of GABA. This review sheds light on developing GABA-enriched plant varieties and food products, and provides insights for efficient production of GABA through synthetic biology approaches.

Comparison of physicochemical properties, amino acids, mineral elements, total phenolic compounds, and antioxidant capacity of Cuban fruit and rice wines

Physicochemical characterization, amino acids contents, minerals composition, total phenolic compounds, and antioxidant capacity of Cuban wines from different raw materials were studied. The wines studied were grape wines, tropical fruit wines, and rice wines. Twenty-one amino acids were identified and quantified, being Asp and Glu detected in all wines. The highest concentration of total amino acid content was found in wines elaborated from Cimarrona grape subjected to maceration with grape skins, while the raisined mixture grape wine presented the lowest values, probably caused by the amino acid degradation during the dehydration process by sun exposure. Minerals quantified were range amount limits of acceptable according to the OIV recommendation. Total phenolic compounds and antioxidant capacity showed the greatest values in wine from roasting rice. No statistical separation could be clearly observed by multivariate principal component analysis; however, 3 wine groups could be defined taking account the scores on the PC1.

Wheat Bran Modifications for Enhanced Nutrition and Functionality in Selected Food Products

The established use of wheat bran (WB) as a food ingredient is related to the nutritional components locked in its dietary fibre. Concurrently, the technological impairment it poses has impeded its use in product formulations. For over two decades, several modifications have been investigated to combat this problem. Ninety-three (93) studies (review and original research) published in English between January 1997 and April 2021 reporting WB modifications for improved nutritional, structural, and functional properties and prospective utilisation in food formulations were included in this paper. The modification methods include mechanical (milling), bioprocessing (enzymatic hydrolysis and fermentation with yeasts and bacteria), and thermal (dry heat, extrusion, autoclaving), treatments. This review condenses the current knowledge on the single and combined impact of various WB pre-treatments on its antioxidant profile, fibre solubilisation, hydration properties, microstructure, chemical properties, and technological properties. The use of modified WB in gluten-free, baked, and other food products was reviewed and possible gaps for future research are proposed. The application of modified WB will have broader application prospects in food formulations.

Probiotic potential of γ-aminobutyric acid (GABA)-producing yeast and its influence on the quality of cheese

Kazakh cheese is a traditional dairy product in Xinjiang, China. To study the function and potential probiotic characteristics of yeast in Kazakh cheese and its contribution to cheese fermentation, we screened the γ-aminobutyric acid (GABA)-producing yeasts Pichia kudriavzevii 1-21, Kluyveromyces marxianus B13-5, Saccharomyces cerevisiae DL6-20, and Kluyveromyces lactis DY1-10. We investigated the potential probiotic properties of these strains and their use in cheese fermentation (cheeses designated CSP, CSM, CSS, and CSI, respectively); a control with no added yeast was designated CS. The results showed that the 4 yeast strains all showed high self-polymerization (2- and 24-h autoaggregation capacity of >80 and 90%, respectively), hydrophobicity (40-92% variation, low hydrophobicity in xylene, but within the range of probiotics), and the ability to survive the gastrointestinal tract (survival rate >75% after simulation), indicating the probiotic ability of the strains in vitro. The GABA production capacity of the CSM cheese increased (to 95.6 mg/100 g), but its protein content did not change significantly, and amino acid degradation was obvious. The GABA production capacity of the CSS cheese decreased (to 450 mg/kg); its protein content declined, and its amino acid content increased. Except for water and protein, we found no obvious differences in most physical and chemical indicators. Kluyveromyces marxianus B13-5 helped to form the desired texture. Multivariate statistical analysis showed that fermentation of the cheese with the 4 yeasts improved the production of esters and alcohols. The CSS cheese had good aroma production performance, because S. cerevisiae DL6-20 produced high concentrations of isoamyl alcohol, hexanoic acid ethyl ester, benzyl alcohol, octanoic acid ethyl ester, 3-hydroxy-2-butanone, and hexanoic acid; the content of 2-methyl-propanoic acid was low. Compared with the CSP cheese, the CSI and CSM cheeses had a fruitier aroma and a milder odor, but the CSI and CSM cheeses had high concentrations of ethyl acetate, butanoic acid, ethyl ester, 3-methyl-1-butanol-acetate, ethyl hexanoate, ethyl octanoate, acetic acid 2-phenylethyl ester, and ethyl lactate; concentrations of 3-methyl-butanoic acid, propanoic acid, acetic acid, and butanoic acid were low. The CSP cheese had stronger acid-producing ability. The order of fragrance production performance was CSS > CSI, CSM > CSP > CS. Research into the fermentation mechanisms of GABA-producing yeast in cheese will provide a theoretical basis for the quality control and industrial production of Kazakh cheese.

Microbial production of gamma-aminobutyric acid: applications, state-of-the-art achievements, and future perspectives

Gamma-aminobutyric acid (GABA) is an important non-protein amino acid with wide-ranging applications. Currently, GABA can be produced by a variety of methods, including chemical synthesis, plant enrichment, enzymatic methods, and microbial production. Among these methods, microbial production has gained increasing attention to meet the strict requirements of an additive in the fields of food, pharmaceutical, and livestock. In addition, renewable and abundant resources, such as glucose and lignocellulosic biomass can also be used for GABA microbial production under mild and environmentally friendly processing conditions. In this review, the applications, metabolic pathways and physiological functions of GABA in different microorganisms were firstly discussed. A comprehensive overview of the current status of process engineering strategies for enhanced GABA production, including fermentation optimization and whole-cell conversion from different feedstocks by various host strains is also provided. We also presented the state-of-the-art achievements in strain development strategies for industrial lactic acid bacteria (LAB), Corynebacterium glutamicum and Escherichia coli to enhance the performance of GABA bioproduction. In order to use bio-based GABA in the fields of food and pharmaceutical, some Generally Recognized as Safe (GRAS) strains such as LAB and C. glutamicum will be the promising chassis hosts. Toward the end of this review, current challenges and valuable research directions/strategies on the improvements of process and strain engineering for economic microbial production of GABA are also suggested.

Rapid evaluation of γ-aminobutyric acid in foodstuffs by direct real-time mass spectrometry

Direct analysis in real-time ionization coupled with mass spectrometry (DART-MS) was first applied for the rapid determination of gamma-aminobutyric acid (GABA) in foods. Samples of germinated barley and fermented beans containing GABA at different levels were used, and the results were compared with those obtained by ultrahigh-performance liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry (UHPLC-ESI-MS). After a series of optimization, a simple sample extraction procedure using 30% methanol aqueous solution was conducted, followed by direct determination of sample extracts without chromatographic separation or prior derivatization. The optimized DART-MS method exhibited low limits of detection (0.040 mg·kg^-1) and good recovery rates (88.6%-104%). The Aspergillus oryzae-fermented black beans produced the highest amount GABA. The results for the samples slightly varied between DART-MS and UHPLC-ESI-MS. Current findings indicate that DART-MS could be a high-throughput alternative to classic UHPLC-ESI-MS.

Comparative Study on the Bread Making Quality of Normoxia- and Hypoxia-Germinated Wheat: Evolution of γ-Aminobutyric Acid, Starch Gelatinization, and Gluten Polymerization during Steamed Bread Making

To explore the bread making characteristics of germinated wheat flour, the current study focused on the componential evolution throughout the steamed bread making process. Hypoxia-germinated wheat (HGW) dough produced the maximum γ-aminobutyric acid as a result of high glutamic acid decarboxylase activity during fermentation compared to normoxia-germinated wheat (NGW) and sound wheat (SW). HGW was superior to NGW in terms of rheological properties and restored the organoleptic characteristics as SW bread. Blocking of α-amylase activity and protein polymerization demonstrated that the decline in pasting and gelation properties was not caused by changes in intrinsic starch and protein properties. Polymerization of α- and γ-gliadin to glutenin was facilitated in germinated wheat bread, while the cross-linking degree of glutenin-gliadin was suppressed. In comparison to NGW bread, more high-molecular-weight glutenin subunits but less α-gliadin fractions polymerized upon steaming of HGW dough. Results demonstrate that HGW has great potential to be exploited as a nutritious functional ingredient for wheat-based food.

On-line near-infrared spectroscopy optimizing and monitoring biotransformation process of γ-aminobutyric acid

Near-infrared spectroscopy (NIRS) with its fast and nondestructive advantages can be qualified for the real-time quantitative analysis. This paper demonstrates that NIRS combined with partial least squares (PLS) regression can be used as a rapid analytical method to simultaneously quantify l-glutamic acid (l-Glu) and γ-aminobutyric acid (GABA) in a biotransformation process and to guide the optimization of production conditions when the merits of NIRS are combined with response surface methodology. The high performance liquid chromatography (HPLC) reference analysis was performed by the o-phthaldialdehyde pre-column derivatization. NIRS measurements of two batches of 141 samples were firstly analyzed by PLS with several spectral pre-processing methods. Compared with those of the HPLC reference analysis, the resulting determination coefficients (R2), root mean square error of prediction (RMSEP) and residual predictive deviation (RPD) of the external validation for the l-Glu concentration were 99.5%, 1.62 g/L, and 11.3, respectively. For the GABA concentration, R2, RMSEP, and RPD were 99.8%, 4.00 g/L, and 16.4, respectively. This NIRS model was then used to optimize the biotransformation process through a Box-Behnken experimental design. Under the optimal conditions without pH adjustment, 200 g/L l-Glu could be catalyzed by 7148 U/L glutamate decarboxylase (GAD) to GABA, reaching 99% conversion at the fifth hour. NIRS analysis provided timely information on the conversion from l-Glu to GABA. The results suggest that the NIRS model can not only be used for the routine profiling of enzymatic conversion, providing a simple and effective method of monitoring the biotransformation process of GABA, but also be considered to be an optimal tool to guide the optimization of production conditions.

Study of the rapid detection of γ-aminobutyric acid in rice wine based on chemometrics using near infrared spectroscopy

Rice wine, in which γ-aminobutyric acid is present, is beneficial to human health and is one of the three most well-known fermented wines in the world, and is very popular in China. The rapid detection of γ-aminobutyric acid was studied in rice wine using near infrared spectroscopy with an optical fibre probe. Through the selection of detection conditions, including a waveband range of 12500-4000 cm(-1), a scanning duration of 16 scans and a resolution of 8 cm(-1), the near infrared spectrum of rice wine was acquired three times, for every wine sample, with an optical fibre probe. The resulting average value of the spectrum was obtained and the corresponding data were analysed via normalization. By adopting a multivariate calibration partial least squares method (PLS) and establishing a calibration model, the highest precision for γ-aminobutyric acid in rice wine was predicted when the factor coefficient was 17. The overall results demonstrating the content of γ-aminobutyric acid in rice wine was predicted to be between 157.6696-317.5813 mg/L, with a relative standard deviation of prediction between 0.01-5 %, as well as the fact that the single sample measuring time was less than 20 s, prove that near infrared spectroscopy is a rapid, accurate and effective method to adopt for detecting the content of γ-aminobutyric acid in rice wine.

Effects of NaCl Replacement with Gamma-Aminobutyric acid (GABA) on the Quality Characteristics and Sensorial Properties of Model Meat Products

This study investigated the effects of γ-aminobutylic acid (GABA) on the quality and sensorial properties of both the GABA/NaCl complex and model meat products. GABA/NaCl complex was prepared by spray-drying, and the surface dimensions, morphology, rheology, and saltiness were characterized. For model meat products, pork patties were prepared by replacing NaCl with GABA. For characteristics of the complex, increasing GABA concentration increased the surface dimensions of the complex. However, GABA did not affect the rheological properties of solutions containing the complex. The addition of 2% GABA exhibited significantly higher saltiness than the control (no GABA treatment). In the case of pork patties, sensory testing indicated that the addition of GABA decreased the saltiness intensity. Both the intensity of juiciness and tenderness of patties containing GABA also scored lower than the control, based on the NaCl reduction. These results were consistent with the quality characteristics (cooking loss and texture profile analysis). Nevertheless, overall acceptability of the pork patties showed that up to 1.5%, patties containing GABA did not significantly differ from the control. Consequently, the results indicated that GABA has a potential application in meat products, but also manifested a deterioration of quality by the NaCl reduction, which warrants further exploration.