Optimization of fermentation for γ-aminobutyric acid (GABA) production by yeast Kluyveromyces marxianus C21 in okara (soybean residue)

Insights and progress on the biosynthesis, metabolism, and physiological functions of gamma-aminobutyric acid (GABA): a review

GABA (γ-aminobutyric acid) is a non-protein amino acid that occurs naturally in the human brain, animals, plants and microorganisms. It is primarily produced by the irreversible action of glutamic acid decarboxylase (GAD) on the α-decarboxylation of L-glutamic acid. As a major neurotransmitter in the brain, GABA plays a crucial role in behavior, cognition, and the body's stress response. GABA is mainly synthesized through the GABA shunt and the polyamine degradation pathways. It works through three receptors (GABAA, GABAB, and GABAC), each exhibiting different pharmacological and physiological characteristics. GABA has a variety of physiological roles and applications. In plants, it regulates growth, development and stress responses. In mammals, it influences physiological functions such as nervous system regulation, blood pressure equilibrium, liver and kidneys enhancement, hormone secretion regulation, immunity enhancement, cancer prevention, as well as anti-aging effects. As a biologically active ingredient, GABA possesses unique physiological effects and medicinal value, leading to its widespread application and substantially increased market demand in the food and pharmaceutical industries. GABA is primarily produced through chemical synthesis, plant enrichment and microbial fermentation. In this review, we first make an overview of GABA, focusing on its synthesis, metabolism, GABA receptors and physiological functions. Next, we describe the industrial production methods of GABA. Finally, we discuss the development of ligands for the GABA receptor binding site, the prospects of GABA production and application, as well as its clinical trials in potential drugs or compounds targeting GABA for the treatment of epilepsy. The purpose of this review is to attract researchers from various fields to focus on GABA research, promote multidisciplinary communications and collaborations, break down disciplinary barriers, stimulate innovative research ideas and methods, and advance the development and application of GABA in medicine, agriculture, food and other fields.

Hybrid substrate-based pH autobuffering GABA fermentation by Levilactobacillus brevis CD0817

The probiotic fermentation of the bioactive substance gamma-aminobutyric acid (GABA) is an attractive research topic. There is still room for further improvement in reported GABA fermentation methods based on a single substrate (L-glutamic acid or L-monosodium glutamate). Here, we devised a pH auto-buffering strategy to facilitate the fermentation of GABA by Levilactobacillus brevis CD0817. This strategy features a mixture of neutral monosodium L-glutamate plus acidic L-glutamic acid as the substrate. This mixture provides a mild initial pH; moreover, the newly dissolved L-glutamic acid automatically offsets the pH increase caused by substrate decarboxylation, maintaining the acidity essential for GABA fermentation. In this study, a flask trial was first performed to optimize the GABA fermentation parameters of Levilactobacillus brevis CD0817. The optimized parameters were further validated in a 10 L fermenter. The flask trial results revealed that the appropriate fermentation medium was composed of powdery L-glutamic acid (750 g/L), monosodium L-glutamate (34 g/L [0.2 mol/L]), glucose (5 g/L), yeast extract (35 g/L), MnSO4·H2O (50 mg/L [0.3 mmol/L]), and Tween 80 (1.0 g/L). The appropriate fermentation temperature was 30 °C. The fermenter trial results revealed that GABA was slowly synthesized from 0-4 h, rapidly synthesized until 32 h, and finally reached 353.1 ± 8.3 g/L at 48 h, with the pH increasing from the initial value of 4.56 to the ultimate value of 6.10. The proposed pH auto-buffering strategy may be popular for other GABA fermentations.

Unraveling the Potential of γ-Aminobutyric Acid: Insights into Its Biosynthesis and Biotechnological Applications

γ-Aminobutyric acid (GABA) is a widely distributed non-protein amino acid that serves as a crucial inhibitory neurotransmitter in the brain, regulating various physiological functions. As a result of its potential benefits, GABA has gained substantial interest in the functional food and pharmaceutical industries. The enzyme responsible for GABA production is glutamic acid decarboxylase (GAD), which catalyzes the irreversible decarboxylation of glutamate. Understanding the crystal structure and catalytic mechanism of GAD is pivotal in advancing our knowledge of GABA production. This article provides an overview of GAD's sources, structure, and catalytic mechanism, and explores strategies for enhancing GABA production through fermentation optimization, metabolic engineering, and genetic engineering. Furthermore, the effects of GABA on the physiological functions of animal organisms are also discussed. To meet the increasing demand for GABA, various strategies have been investigated to enhance its production, including optimizing fermentation conditions to facilitate GAD activity. Additionally, metabolic engineering techniques have been employed to increase the availability of glutamate as a precursor for GABA biosynthesis. By fine-tuning fermentation conditions and utilizing metabolic and genetic engineering techniques, it is possible to achieve higher yields of GABA, thus opening up new avenues for its application in functional foods and pharmaceuticals. Continuous research in this field holds immense promise for harnessing the potential of GABA in addressing various health-related challenges.

In Vitro Characterization and Identification of Potential Probiotic Yeasts Isolated from Zaopocu, a Traditional Fermented Dregs Vinegar from Hainan Island

Recently, there has been an increasing interest in researching fermented food-derived yeasts as probiotics because they offer a natural and diverse source of potential strains with unique functional properties and health benefits. In this study, 13 yeast strains isolated from Zaopocu (ZPC), a traditional fermented dregs vinegar on Hainan Island, China, were evaluated for their probiotic characteristics in vitro. Yeast identification was conducted through 5.8S-ITS region sequencing, revealing Kodamaea ohmeri as the predominantly isolated species (ZPC_Y3, Y5, Y6, Y11), followed by Pichia kudriavzevii (ZPC_Y2, Y13, Y14), Rhodotorula mucilaginosa (ZPC_Y9, Y10), Pichia fermentans (ZPC_Y8, Y12), Pichia kluyveri (ZPC_Y4), and Pichia occidentalis (ZPC_Y1). Except for ZPC_Y4, ZPC_Y8, and ZPC_Y12, all isolated yeasts exhibited stable growth at 37 °C. The survival rates of all test strains exceeded 60% under challenging conditions at pH = 2 and 0.3% bile salt, along with strong antioxidant activity (> 5 6%), notable autoaggregation (> 70%), and varying levels of cell hydrophobicity with xylene (ranging from 35.32 ± 8.57% to 89.73 ± 4.84%). In addition, all isolates showed resistance to multiple antibiotics, along with antagonistic activity, and were deemed safe as none exhibited hemolytic, gelatinase, or DNase activities. Significantly, two P. kudriavzevii strains (ZPC_Y2, Y14) exhibited the production of catalase, lipase, and β-galactosidase, along with the capacity to synthesize gamma-aminobutyric acid (GABA). In summary, this preliminary study represents the first attempt to identify and characterize potential probiotic yeast strains isolated from Zaopocu, providing a theoretical basis for exploring their application in developing novel therapeutic probiotics.

Lactobacillus brevis M2-Fermented Whey Protein Hydrolysate Increases Slow-Wave Sleep via GABAA Receptors in Rodent Models

In this study, we investigated the effects of whey protein hydrolysate (WPH) fermented with Lactobacillus brevis on sleep behavior and GABAergic mechanisms in rodent models. Fermentation converted the glutamate in WPH to high (3.15 ± 0.21 mg/mL) levels of γ-aminobutyric acid (GABA). Fermented WPH (WP-SF) enhanced sleep duration in mice by increasing GABA content in the brain. The increase in sleep duration induced by WP-SF resulted from an increase in delta wave activity during non-rapid eye movement sleep, and its sleep-promoting effect in a caffeine-induced insomnia model was characterized by an increase in delta waves. WP-SF increased GABAergic receptors at both mRNA and protein levels. Cotreatment with GABAA receptor antagonists abolished the sleep-promoting effects of WP-SF, indicating that WP-SF shares binding sites with antagonists on GABAA receptors. Collectively, WP-SF effectively increased sleep duration by enhancing delta wave activity through GABAergic activation; thus, it is suggested as a functional food-grade ingredient for promoting sleep.

Succinic acid production by wine yeasts and the influence of GABA and glutamic acid

As a consequence of alcoholic fermentation (AF) in wine, several compounds are released by yeasts, and some of them are linked to the general quality and mouthfeel perceptions in wine. However, others, such as succinic acid, act as inhibitors, mainly of malolactic fermentation. Succinic acid is produced by non-Saccharomyces and Saccharomyces yeasts during the initial stages of AF, and the presence of some amino acids such as γ-aminobutyric acid (GABA) and glutamic acid can increase the concentration of succinic acid. However, the influence of these amino acids on succinic acid production has been studied very little to date. In this work, we studied the production of succinic acid by different strains of non-Saccharomyces and Saccharomyces yeasts during AF in synthetic must, and the influence of the addition of GABA or glutamic acid or a combination of both. The results showed that succinic acid can be produced by non-Saccharomyces yeasts with values in the range of 0.2-0.4 g/L. Moreover, the addition of GABA or glutamic acid can increase the concentration of succinic acid produced by some strains to almost 100 mg/L more than the control, while other strains produce less. Consequently, higher succinic acid production by non-Saccharomyces yeast in coinoculated fermentations with S. cerevisiae strains could represent a risk of inhibiting Oenococcus oeni and therefore the MLF.

Recent advances in the biosynthesis and industrial biotechnology of Gamma-amino butyric acid

GABA (Gamma-aminobutyric acid), a crucial neurotransmitter in the central nervous system, has gained significant attention in recent years due to its extensive benefits for human health. The review focused on recent advances in the biosynthesis and production of GABA. To begin with, the investigation evaluates GABA-producing strains and metabolic pathways, focusing on microbial sources such as Lactic Acid Bacteria, Escherichia coli, and Corynebacterium glutamicum. The metabolic pathways of GABA are elaborated upon, including the GABA shunt and critical enzymes involved in its synthesis. Next, strategies to enhance microbial GABA production are discussed, including optimization of fermentation factors, different fermentation methods such as co-culture strategy and two-step fermentation, and modification of the GABA metabolic pathway. The review also explores methods for determining glutamate (Glu) and GABA levels, emphasizing the importance of accurate quantification. Furthermore, a comprehensive market analysis and prospects are provided, highlighting current trends, potential applications, and challenges in the GABA industry. Overall, this review serves as a valuable resource for researchers and industrialists working on GABA advancements, focusing on its efficient synthesis processes and various applications, and providing novel ideas and approaches to improve GABA yield and quality.

Bidirectional fermentation of Monascus and Mulberry leaves enhances GABA and pigment contents: establishment of strategy, studies of bioactivity and mechanistic

Bidirectional fermentation is a technology that utilizes fungi to ferment medicinal edible substrates, with synergistic and complementary advantages. In this work, a fermentation strategy was established to produce a high yield of γ-aminobutyric acid (GABA) and Monascus pigments (MPs) using Monascus and mulberry leaves (MLs). Firstly, the basic fermentation parameters were determined using single-factor experiments, followed by Plackett-Burman (PB) experimental design to identify MLs, glucose, peptone, and temperature as significant influencing factors. The fermentation parameters were optimized using an artificial neural network (ANN). Finally, the effects of bidirectional fermentation of MLs and Monascus were investigated by bioactivity analysis, microstructure observation, and RT-qPCR. The outcomes showed that the bidirectional fermentation significantly increased the bioactive content and promoted the secondary metabolism of Monascus. The established fermentation conditions were 44.2 g/L of MLs, 57 g/L of glucose, 15 g/L of peptone, 1 g/L of MgSO4, 2 g/L of KH2PO4, 8% (v/v) of inoculum, 180 rpm, initial pH 6, 32 °C and 8 days. The content of GABA reached 13.95 g/L and the color value of MPs reached 408.07 U/mL. This study demonstrated the feasibility of bidirectional fermentation of MLs and Monascus, providing a new idea for the application of MLs and Monascus.

Biosynthesis of Gamma-Aminobutyric Acid (GABA) by Lactiplantibacillus plantarum in Fermented Food Production

In recent decades, given the important role of gamma-aminobutyric acid (GABA) in human health, scientists have paid great attention to the enrichment of this chemical compound in food using various methods, including microbial fermentation. Moreover, GABA or GABA-rich products have been successfully commercialized as food additives or functional dietary supplements. Several microorganisms can produce GABA, including bacteria, fungi, and yeasts. Among GABA-producing microorganisms, lactic acid bacteria (LAB) are commonly used in the production of many fermented foods. Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a LAB species that has a long history of natural occurrence and safe use in a wide variety of fermented foods and beverages. Within this species, some strains possess not only good pro-technological properties but also the ability to produce various bioactive compounds, including GABA. The present review aims, after a preliminary excursus on the function and biosynthesis of GABA, to provide an overview of the current uses of microorganisms and, in particular, of L. plantarum in the production of GABA, with a detailed focus on fermented foods. The results of the studies reported in this review highlight that the selection of new probiotic strains of L. plantarum with the ability to synthesize GABA may offer concrete opportunities for the design of new functional foods.

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.

A Novel Method for γ-Aminobutyric Acid Biosynthesis Using Glutamate Decarboxylase Entrapped in Polyvinyl Alcohol-Sodium Alginate Capsules

γ-aminobutyric acid (GABA) has essential physiological functions in the human body. A novel method using glutamate decarboxylase (GAD) entrapped in polyvinyl alcohol (PVA)-sodium alginate (SA) capsules provides a green biological strategy for GABA synthesis. In this investigation, the stability range of immobilized GAD was effectively broadened, and immobilized GAD could be repeatedly used as a batch and fixed-bed column catalyst. The immobilized enzymes were stable and retained 89% of their activity in a pH range of 4.0-5.6, while there was an approximately 50% decrease in free GAD activity in the pH range of 4.8 ± 0.4. The immobilized GAD affinity to the substrate improved, and this was evidenced by the apparent decrease in Km to 13.3 mmol/L from the 30.9 mmol/L for free GAD. The immobilized GAD retained >90.6% activity after eight cycles and a near-100% enzyme activity retention after 120 h of a continuous fixed-bed column catalyst operation. This study has thus presented an effective PVA-SA-GAD immobilization method that could be used to continuously scale-up GABA biosynthesis.

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.

Yeasts originating from fermented foods, their potential as probiotics and therapeutic implication for human health and disease

Yeasts derived from fermented foods have historically been known for their organoleptic properties, enriching nutritional values, and producing bioactive metabolites with therapeutic potential. In this review, we discuss the yeast flora in fermented foods, their functional aspects in fermentation, as well as their probiotic and biotherapeutic properties. These yeasts have numerous physical and biochemical characteristics, such as larger cells as compared to bacteria, a rigid cell wall composed primarily of glucans and mannans, natural resistance to antibiotics, and the secretion of secondary metabolites that are both pleasing to the consumer and beneficial to the host's health and well-being. The review also focused on therapeutic applications of probiotic yeasts derived from fermented foods on infections associated with Candida species. These potential probiotic yeasts present an additional avenue to treat dysbiosis of the gut microbiota and prevent health complications that arise from opportunistic fungal colonization, especially drug-resistant superbugs, which are highlighted in this review.