Gamma-aminobutyric acid production in black soybean milk by Lactobacillus brevis FPA 3709 and the antidepressant effect of the fermented product on a forced swimming rat model

Probiotics and the microbiota-gut-brain axis in neurodegeneration: Beneficial effects and mechanistic insights

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders with a high socioeconomic burden. Although pharmacotherapy is currently the principal therapeutic approach for the management of NDs, mounting evidence supports the notion that the protracted application of available drugs would abate their dopaminergic outcomes in the long run. The therapeutic application of microbiome-based modalities has received escalating attention in biomedical works. In-depth investigations of the bidirectional communication between the microbiome in the gut and the brain offer a multitude of targets for the treatment of NDs or maximizing the patient's quality of life. Probiotic administration is a well-known microbial-oriented approach to modulate the gut microbiota and potentially influence the process of neurodegeneration. Of note, there is a strong need for further investigation to map out the mechanistic prospects for the gut-brain axis and the clinical efficacy of probiotics. In this review, we discuss the importance of microbiome modulation and hemostasis via probiotics, prebiotics, postbiotics and synbiotics in ameliorating pathological neurodegenerative events. Also, we meticulously describe the underlying mechanism of action of probiotics and their metabolites on the gut-brain axis in different NDs. We suppose that the present work will provide a functional direction for the use of probiotic-based modalities in promoting current practical treatments for the management of neurodegenerative-related diseases.

Gut health benefits and associated systemic effects provided by functional components from the fermentation of natural matrices

Recently, the role of the gut microbiota in metabolic health, immunity, behavioral balance, longevity, and intestine comfort has been the object of several studies from scientific communities. They were encouraged by a growing interest from food industries and consumers toward novel fermented ingredients and formulations with powerful biological effects, such as pre, pro, and postbiotic products. Depending on the selected strains, the operating conditions, the addition of suitable reagents or enzymes, the equipment, and the reactor configurations, functional compounds with high bioactivity, such as short-chain fatty acids, gamma-aminobutyric acid, bioactive peptides, and serotonin, can be enhanced and/or produced through fermentation of several vegetable matrices. Otherwise, their formation can also be promoted directly in the gut after the dietary intake of fermented foods: In this case, fermentation will aim to increase the content of precursor substances, such as indigestible fibers, polyphenols, some amino acids, and resistant starch, which can be potentially metabolized by endogenous gut microorganisms and converted in healthy molecules. This review provides an overview of the main functional components currently investigated in literature and the associated gut health benefits. The current state of the art about fermentation technology as a promising functionalization tool to promote the direct or indirect formation of gut-health-enhancing components was deepened, highlighting the importance of optimizing microorganism selection, system setups, and process conditions according to the target compound of interest. The collected data suggested the possibility of gaining novel functional food ingredients or products rich in functional molecules through fermentation without performing additional extraction and purification stages, which are needed when conventional culture broths are used.

Culture-dependent and -independent analyses of bacterial compositions and its contributions to formation of γ-aminobutyric acid and poly-γ-glutamic acid in Cheonggukjang

This study was performed to unveil bacterial compositions and their contributions to the formation of γ-aminobutyric acid (GABA) and poly-γ-glutamic acid (γ-PGA) in Cheonggukjang. To predict possible key factors contributing to the content of the bioactive compounds in Cheonggukjang, commercial products were analyzed for various parameters. The content of GABA and γ-PGA showed a negative (R2 = 0.61 - 0.73) and positive correlation (R2 = 0.53 - 0.96) with antioxidative activity. Consistently, GABA content showed a moderate negative correlation with γ-PGA content (R2 = 0.58). Among the physicochemical and microbial parameters, only salinity showed a moderate negative correlation with γ-PGA content (R2 = 0.75), which might be due to the inhibition of bacterial growth. It was also suggested that multiple factors (including bacterial species) were involved in the formation of GABA and γ-PGA in Cheonggukjang. To reveal dominant bacterial species and further presume their contributions to the bioactive compound formation in Cheonggukjang, both culture-independent (metagenomic) and -dependent (culturomic) methods were used. Culture-independent method showed that Bacillus piscis was dominant (23.37 - 94.89 %), followed by B. hisashii (0.00 - 62.45 %) and B. coagulans (0.00 - 13.82 %). Considering the quantitative speciation data on the bioactive compound content in Cheonggukjang (and bacterial production capability) together, it was further elucidated that B. piscis contributed primarily to the bioactive compound formation. Unlike this, culture-dependent analysis revealed that B. licheniformis and B. subtilis were dominant (30.0 - 47.6 and 17.5 - 39.5 %, respectively). Based on the quantitative speciation data on the bacterial production capability of GABA and γ-PGA, B. subtilis was the primarily contributing bacterial species to the bioactive compound formation. Consequently, it was observed that the bacterial compositions and their contributions to the bioactive compound formation determined by the two methods differed considerably, i.e., B. piscis and B. subtilis were identified to be prominent bacterial contributors, respectively, depending on the method used.

Gamma Amino Butyric Acid (GABA) and Ferulic Acid Esterase (FAE) Producing Psychobiotic Bacteria Isolated from Cereal-Based Fermented Food

Gut microbiota plays an important role in regulating enteric, immune and neural pathways. Many neuropsychiatric disorders such as anxiety, depression, autism and cognitive behaviour are associated with gut dysbiosis. Gamma-aminobutyric acid (GABA) and short-chain fatty acids produced by gut bacteria influence gastrointestinal and neurological functions. Ferulic acid esterase (FAE) which releases ferulic acid (FA) from feruloylated sugar ester conjugates, naturally found in grains, fruits and vegetables, is also produced by some gut bacteria and helps prevent neurodegeneration. These properties provide bacteria with the ability to maintain intestinal barrier function and prevent neuropsychiatric disorders. Therefore, this study aims to isolate GABA and FAE-producing LAB and characterize their bioactive and probiotic properties. A total of twelve cultures were isolated, of which eight bacteria positive for GABA, FAE and SCFA production were selected for further investigation. All selected bacteria were positive for bile salt hydrolase (BSH) and showed acid tolerance, resistance to bile salt, stimulated gastric and pancreatic juice, and auto- and co-aggregation properties. Furthermore, selected LAB showed mucin adhesion efficiency greater than 80% and exhibited γ-hemolytic activity. 16S rRNA sequencing identified NS0969, B1, C1, C2, M1, M2, and R2 as Limosilactobacillus fermentum and R1 as Lactiplantibacillus pentosus. This study showed that selected bacteria and/or their postbiotic preparations can be used as potential psychobiotics.

Potential of γ-Aminobutyric Acid-Producing Leuconostoc mesenteroides Strains Isolated from Kimchi as a Starter for High-γ-Aminobutyric Acid Kimchi Fermentation

γ-Aminobutyric acid (GABA)-producing Leuconostoc mesenteroides K1501 and K1627, isolated from kimchi, exhibited the highest GABA production in 1% monosodium glutamic acid. Both strains showed high survival rates of approximately 87% in artificial gastric juice (pH 3.0) and >80% in 0.1% artificial bile salt fluid. The survival rate was approximately 28% in 0.3% artificial bile salt fluid and 0% in 0.5% artificial bile salts. Both strains showed excellent adhesion to intestinal epithelial cells (>99%). Furthermore, it was observed that growth was not inhibited at 2% salt concentration; however, it was slightly retarded at salt concentrations of 3% and 4%. Moreover, L. mesenteroides K1501 and K1627 inhibited the growth of certain species of Lactobacillus, whose presence in kimchi fermentation is undesirable. Therefore, L. mesenteroides K1501 and K1627 have the potential to be used as starter organisms for functional GABA-rich kimchi.

Ascertaining the Influence of Lacto-Fermentation on Changes in Bovine Colostrum Amino and Fatty Acid Profiles

The aim of this study was to collect samples of bovine colostrum (BCOL) from different sources (agricultural companies A, B, C, D and E) in Lithuania and to ascertain the influence of lacto-fermentation with Lactiplantibacillus plantarum strain 135 and Lacticaseibacillus paracasei strain 244 on the changes in bovine colostrum amino (AA), biogenic amine (BA), and fatty acid (FA) profiles. It was established that the source of the bovine colostrum, the used LAB, and their interaction had significant effects (p < 0.05) on AA contents; lactic acid bacteria (LAB) used for fermentation was a significant factor for aspartic acid, threonine, glycine, alanine, methionine, phenylalanine, lysine, histidine, and tyrosine; and these factor's interaction is significant on most of the detected AA concentrations. Total BA content showed significant correlations with glutamic acid, serine, aspartic acid, valine, methionine, phenylalanine, histidine, and gamma amino-butyric acid content in bovine colostrum. Despite the differences in individual FA contents in bovine colostrum, significant differences were not found in total saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids. Finally, the utilization of bovine colostrum proved to be challenging because of the variability on its composition. These results suggest that processing bovine colostrum into value-added formulations for human consumption requires the adjustment of its composition since the primary production stage. Consequently, animal rearing should be considered in the employed bovine colostrum processing technologies.

Psychobiotics: Are they the future intervention for managing depression and anxiety? A literature review

Mental health is a public health concern among professional organizations, clinicians, and consumers alike, especially in light of the COVID-19 pandemic. Indeed, the World Health Organization has identified mental health as an epidemic of the 21st century contributing to the global health burden, which highlights the urgency to develop economical, accessible, minimally invasive interventions to effectively manage depression, anxiety, and stress. Nutritional approaches, including the use of probiotics and psychobiotics to manage depression and anxiety, have elicited interest in recent years. This review aimed to summarize evidence from studies including animal models, cell cultures, and human subjects. Overall, the current evidence suggests that 1) Specific strains of probiotics can reduce depressive symptoms and anxiety; 2) Symptoms may be reduced through one or more possible mechanisms of action, including impact on the synthesis of neurotransmitters such as serotonin and GABA, modulation of inflammatory cytokines, or enhancing stress responses through effects on stress hormones and the HPA axis; and 3) While psychobiotics may offer therapeutic benefits to manage depression and anxiety, further research, particularly human studies, is needed to better characterize their mode of action and understand optimal dosing in the context of nutritional interventions.

Production of glycerolamines based conjugated γ-aminobutyric acids using microbial COX and LOX as successor enzymes to GAD

Gamma-aminobutyric acid (γ-ABA) can be produced by various microorganisms including bacteria, fungi and yeasts using enzymatic bioconversion, microbial fermentation or chemical hydrolysis. Regenerating conjugated glycerol-amines is valid by the intervention of microbial cyclooxygenase [COX] and lipooxygenase [LOX] enzymes produced via lactobacillus bacteria (LAB) as successor enzymes to glutamate decarboxylases (GAD). Therefore, the aim of this review is to provide an overview on γ-ABA production, and microbiological achievements used in producing this signal molecule based on those fermenting enzymes. The formation of aminoglycerides based conjugated γ-ABA is considered the key substances in controlling the host defense against pathogens and is aimed in increasing the neurotransmission effects and in suppressing further cardiovascular diseases.

Effects of probiotics on GABA/glutamate and oxidative stress in PTZ- induced acute seizure model in rats

Studies conducted in recent years have indicated a relationship between epilepsy and gut microbiota. Ion channels, excitatory/inhibitory balance and regulatory systems play a role in the pathophysiology of epilepsy. In addition, gut dysbiosis is also involved in the pathophysiology of epilepsy. This research investigated the impacts of probiotic mixture on epileptic seizures, Gamma aminobutyric acid (GABA), glutamate, and TAS and TOS levels in hippocampal tissue in the PTZ-induced acute seizure model in rats. Four groups were formed with male Wistar albino rats. The first and second groups were given 1 ml/day saline solution, and the other groups were given 0.05 mg/1 ml/day vehicle or 109cfu/1 ml/day probiotic supplementation, respectively via gavage for 21 days. A single-dose PTZ (45 mg/kg) was administered to induce seizure. The stages of seizure were analyzed according to the Racine scale. While ELISA was used to determine GABA and glutamate levels in the hippocampus, an automated colorimetric method was utilized to measure oxidant/antioxidant biomarkers. It was found that by delaying the first myoclonic jerk (FMJ), and the onset of the generalized tonic-clonic seizures, the probiotic mixture demonstrated anticonvulsant effects against seizures. The probiotic mixture was found to increase the inhibitory neurotransmitter GABA. It was also found to decrease TOS levels and increase TAS concentration. The findings of this study showed that probiotic mixture reduced oxidative stress with its positive effects against PTZ-induced epileptic seizures. Further studies are needed to reveal potentially related mechanisms.

Optimization of Gamma-Aminobutyric Acid Production by Lactiplantibacillus plantarum FRT7 from Chinese Paocai

Gamma-aminobutyric acid (GABA) is a widely available non-protein amino acid whose physiological importance goes beyond its role as an inhibitory neurotransmitter in mammals. The GABA synthesis ability of ten strains of Lactiplantibacillus plantarum was screened. They produced GABA ranging from 48.19 ± 3.44 to 100.75 ± 1.63 mg/L at 24 h-cultivation. Among them, Lp. plantarum FRT7 showed the highest GABA production. Therefore, FRT7 was chosen for GABA yield optimization. A one-factor-at-a-time strategy analysis of the GABA yield of FRT7 was performed, including the culture temperature, incubation time, inoculum volume, initial pH, the initial amount of monosodium glutamate (MSG), and pyridoxal 5'-phosphate (PLP) concentration, based on which the response surface methodology (RSM) was performed. After being cultured in an MRS culture medium supplemented with 3% MSG and 2 mmol/L of PLP at 40 °C with an initial pH of 7.0 for 48 h, the GABA reached a maximum yield of 1158.6 ± 21.22 mg/L. The results showed the experimental value of the GABA yield was in good agreement with the predicted values. Furthermore, the results from the RSM also indicated that the initial MSG addition, PLP concentration, and incubation time were significant variables. These results suggest that Lp. plantarum FRT7 has the potential to be a health-beneficial probiotic with commercial capabilities.

Gamma-Aminobutyric Acid (GABA) Biosynthesis from Lactobacillus plantarum subsp. plantarum IBRC10817 Optimized and Modeled in Response to Heat and Ultrasonic Shock

Gamma-aminobutyric acid is one of the major inhibitory neurotransmitters in the nervous system. Although gamma-aminobutyric acid is commonly synthesized by chemical methods, its microbial biosynthesis is regarded as one of the best production methods among the conventional techniques. This study aimed to optimize and model the production of gamma-aminobutyric acid from Lactobacillus plantarum subsp. plantarum IBRC (10,817) under the influence of heat and ultrasonic shock using the response surface methodology. Heat and ultrasonic shock were applied in the lag phase of bacterial growth. Heat shock variables included heat treatment, monosodium glutamate concentration, and incubation time. Also, ultrasonic shock variables were ultrasonic intensity, ultrasonic time, incubation time, and monosodium glutamate concentration. By applying the 30.9 h of incubation, 3.082 g/L of monosodium glutamate, and thermal shock of 49.958 °C for 30 min, the production of 295.04 mg/L of gamma amino butyric acid was predicted. As for ultrasonic shock, using 3.28 (g/L) monosodium glutamate, 70 h of bacterial incubation, 7.7 min ultrasound shock, and ultrasound frequency of 26.58 kHz, the highest amount of metabolite production was anticipated to be 215.19 mg/L. Overall, it was found that the actual values were consistent with the predicted values.

Recent advances in microbial production of diamines, aminocarboxylic acids, and diacids as potential platform chemicals and bio-based polyamides monomers

Recently, bio-based manufacturing processes of value-added platform chemicals and polymers in biorefineries using renewable resources have extensively been developed for sustainable and carbon dioxide (CO₂) neutral-based industry. Among them, bio-based diamines, aminocarboxylic acids, and diacids have been used as monomers for the synthesis of polyamides having different carbon numbers and ubiquitous and versatile industrial polymers and also as precursors for further chemical and biological processes to afford valuable chemicals. Until now, these platform bio-chemicals have successfully been produced by biorefinery processes employing enzymes and/or microbial host strains as main catalysts. In this review, we discuss recent advances in bio-based production of diamines, aminocarboxylic acids, and diacids, which has been developed and improved by systems metabolic engineering strategies of microbial consortia and optimization of microbial conversion processes including whole cell bioconversion and direct fermentative production.

Consumption of fermented dairy products is associated with lower anxiety levels in Azorean university students

A growing number of studies have found that the gut microbiota is involved in a variety of psychological processes and neuropsychiatric disorders, which include mood and anxiety disorders. Consumption of dairy products may contain bioactive compounds and probiotic bacteria with various therapeutic benefits. The aim of the study was to investigate possible associations between the frequency of consumption of different types of dairy products and the state of anxiety in university students. The subjects were 311 Azorean university students, 231 women and 80 men, with an average age of 20.5 years. Subjects completed a quantitative questionnaire on the frequency of dairy product consumption and a short version of the Spielberger State-Trait Anxiety Inventory (STAI) test. Among dairy products, semi-skimmed milk was the most commonly consumed, followed by cheese (ripened), drinking yogurt, skim milk, and set yogurt, while fresh cheese, whole milk, and dairy ice cream were the least common. Discriminant analysis showed that consumption of fermented products (yogurt and cheese) was significantly higher (P < 0.05) in the group with low anxiety level (score <40 in STAI test) than in the group with higher anxiety level (score ≥ 40). In this analysis, 62.4% of the initially grouped cases were correctly classified according to the frequency of fermented products consumption. No correlations were found between anxiety and unfermented dairy products. The results indicate that the consumption of fermented dairy products has a positive effect on reducing anxiety in young Azorean university students.

Lactic Acid Bacteria in Raw-Milk Cheeses: From Starter Cultures to Probiotic Functions

Traditional cheeses produced from raw milk exhibit a complex microbiota, characterized by a sequence of different microorganisms from milk coagulation and throughout maturation. Lactic acid bacteria (LAB) play an essential role in traditional cheese making, either as starter cultures that cause the rapid acidification of milk or as secondary microbiota that play an important role during cheese ripening. The enzymes produced by such dynamic LAB communities in raw milk are crucial, since they support proteolysis and lipolysis as chief drivers of flavor and texture of cheese. Recently, several LAB species have been characterized and used as probiotics that successfully promote human health. This review highlights the latest trends encompassing LAB acting in traditional raw milk cheeses (from cow, sheep, and goat milk), and their potential as probiotics and producers of bioactive compounds with health-promoting effects.

Biological Role of Nutrients, Food and Dietary Patterns in the Prevention and Clinical Management of Major Depressive Disorder

Major Depressive Disorder (MDD) is a growing disabling condition affecting around 280 million people worldwide. This complex entity is the result of the interplay between biological, psychological, and sociocultural factors, and compelling evidence suggests that MDD can be considered a disease that occurs as a consequence of an evolutionary mismatch and unhealthy lifestyle habits. In this context, diet is one of the core pillars of health, influencing multiple biological processes in the brain and the entire body. It seems that there is a bidirectional relationship between MDD and malnutrition, and depressed individuals often lack certain critical nutrients along with an aberrant dietary pattern. Thus, dietary interventions are one of the most promising tools to explore in the field of MDD, as there are a specific group of nutrients (i.e., omega 3, vitamins, polyphenols, and caffeine), foods (fish, nuts, seeds fruits, vegetables, coffee/tea, and fermented products) or dietary supplements (such as S-adenosylmethionine, acetyl carnitine, creatine, amino acids, etc.), which are being currently studied. Likewise, the entire nutritional context and the dietary pattern seem to be another potential area of study, and some strategies such as the Mediterranean diet have demonstrated some relevant benefits in patients with MDD; although, further efforts are still needed. In the present work, we will explore the state-of-the-art diet in the prevention and clinical support of MDD, focusing on the biological properties of its main nutrients, foods, and dietary patterns and their possible implications for these patients.

Psychobiotics: the Influence of Gut Microbiota on the Gut-Brain Axis in Neurological Disorders

Nervous system disorders are one of the common problems that affect many people around the world every year. Regarding the beneficial effects of the probiotics on the gut and the gut-brain axis, their application along with current medications has been the subject of intense interest. Psychobiotics are a probiotic strain capable to affect the gut-brain axis. The effective role of Psychobiotics in several neurological disorders is documented. Consumption of the Psychobiotics containing nutrients has positive effects on the improvement of microbiota as well as alleviation of some symptoms of central nervous system (CNS) disorders. In the present study, the effects of probiotic strains on some CNS disorders in terms of controlling the disease symptoms were reviewed. Finding suggests that Psychobiotics can efficiently alleviate the symptoms of several CNS disorders such as autism spectrum disorders, Parkinson’s disease, multiple sclerosis, insomnia, depression, diabetic neuropathy, and anorexia nervosa. It can be concluded that functional foods containing psychotropic strains can help to improve mental health.

Rhizoma Gastrodiae Water Extract Modulates the Gut Microbiota and Pathological Changes of P-TauThr231 to Protect Against Cognitive Impairment in Mice

Gastrodiae Rhizoma and its active constituents are known to exhibit neuroprotective effects in Alzheimer’s disease (AD). However, the effect of Rhizoma Gastrodiae water extract (WERG) on AD and the detailed mechanism of action remain unclear. In this study, the mechanism of action of WERG was investigated by the microbiome–gut–brain axis using a D-galactose (D-gal)/AlCl₃-induced AD mouse model. WERG improved the cognitive impairment of D-gal/AlCl₃-induced mice. The expression level of p-Tau^thr231 in the WERG-H treatment group was decreased, and p-Tau^thr231 was found negative in hippocampal DG, CA1, and CA3 regions. Here, the diversity and composition of the gut microbiota were analyzed by 16sRNA sequencing. WERG-H treatment had a positive correlation with Firmicutes, Bacilli, Lactobacillus johnsonii, Lactobacillus murinus, and Lactobacillus reuteri. Interestingly, the Rikenellaceae-RC9 gut group in the gut increased in D-gal/AlCl₃-induced mice, but the increased L. johnsonii, L. murinus, and L. reuteri reversed this process. This may be a potential mechanistic link between gut microbiota dysbiosis and P-Tau^Thr231 levels in AD progression. In conclusion, this study demonstrated that WERG improved the cognitive impairment of the AD mouse model by enriching gut probiotics and reducing P-Tau^Thr231 levels.

Intriguing role of Gut-Brain Axis on cognition with emphasis on interaction with Papez circuit

The gut microbiome is a complicated ecosystem of around a hundred billion symbiotic bacteria cells. Bidirectional communication between the gut and the brain is facilitated by the immune system, the enteric nervous system, the vagus nerve, and microbial compounds such as tryptophan metabolites and short-chain fatty acids (SCFAs). The current study emphasises the relationship of the gut-brain axis with cognitive performance and elucidates the underlying biological components, with a focus on neurotransmitters such as serotonin, indole derivatives, and catecholamine. These biological components play important roles in both the digestive and brain systems. Recent research has linked the gut microbiome to a variety of cognitive disorders, including Alzheimer's (AD). The review describes the intriguing role of the gut-brain axis in recognition memory depending on local network connections within the hippocampal as well as other additional hippocampal portions of the Papez circuit. The available data from various research papers show how the gut microbiota might alter brain function and hence psychotic and cognitive illnesses. The role of supplementary probiotics is emphasized for the reduction of brain-related dysfunction as a viable strategy in handling cognitive disorders. Further, the study elucidates the mode of action of probiotics with reported adverse effects.

Current trends in the development of soy-based foods containing probiotics and paving the path for soy-synbiotics

In the world of highly processed foods, special attention is drawn to the nutrient composition and safety of consumed food products. Foods fortified with probiotic bacteria confer beneficial effects on human health and are categorized as functional foods. The salubrious activities of probiotics include the synthesis of vital bioactives, prevention of inflammatory diseases, anticancerous, hypocholesterolemic, and antidiarrheal effects. Soy foods are exemplary delivery vehicles for probiotics and prebiotics and there are diverse strategies to enhance their functionality like employing mixed culture fermentation, engineering probiotics, and incorporating prebiotics in fermented soy foods. High potential is ascribed to the concurrent use of probiotics and prebiotics in one product, termed as "synbiotics," which implicates synergy, in which a prebiotic ingredient particularly favors the growth and activity of a probiotic micro-organism. The insights on emended bioactive profile, metabolic role, and potential health benefits of advanced soy-based probiotic and synbiotic hold a promise which can be profitably implemented to meet consumer needs. This article reviews the available knowledge about strategies to enhance the nutraceutical potential, mechanisms, and health-promoting effects of advanced soy-based probiotics. Traditional fermentation merged with diverse strategies to improve the efficiency and health benefits of probiotics considered vital, are also discussed.

Metabolomic Analysis Reveals Changes of Bioactive Compounds in Mung Beans (Vigna radiata) during γ-Aminobutyric Acid Enrichment Treatment

Soaking together with Heat and Relative Humidity (HRH) treatment has been applied successfully to enrich γ-aminobutyric acid (GABA) in mung beans. However, whether and how the above GABA enrichment processing influences the other bioactive molecules is elusive. In the present study, mung beans were soaked and then treated by HRH for 5 or 7 h. By using metabolomics techniques, the changes of 496 metabolites were determined. The relative content of flavonoids and phenolic acids increased during soaking but slightly decreased during HRH. Intriguingly, soaking and HRH had the opposite effects on the glycosylation of polyphenols. The relative content of glycosylated or un-glycosylated polyphenols increased during soaking or HRH, respectively. The relative content of α-ketoglutaric acid increased more than 20 times after 5 h HRH treatment. Bioactive molecules could be enriched during GABA enrichment processing. Depending on the desired bioactive compounds, soaking and different duration of HRH treatment could be selected.

Application of Enterococcus malodoratus SJC25 for the Manufacture of Whey-Based Beverage Naturally Enriched with GABA

Gamma-aminobutyric acid (GABA) is used as a dietary supplement because of its health-promoting properties. However, concern over the use of synthetic products has increased the demand for foods that are naturally fortified with GABA. In addition, excess whey is a major concern for the dairy industry due to the high cost of treating it. Here, we report the use of a novel Enterococcus malodoratus strain isolated from cheese to produce sweet whey beverages naturally enriched with GABA. After the screening of cheese isolates, E. malodoratus strains were identified as high GABA producers. One beverage was prepared from pasteurized sweet whey enriched in glutamic acid and E. malodoratus SJC25. The fermented beverages were supplemented with a fruit preparation and subjected to chemical, microbiological and sensory analysis. The bacterial counts and GABA content were maintained until storage at 4 °C for 14 days. High conversion rates of glutamic acid to GABA (50–71%) were obtained in the beverages. The GABA content in whey-based beverages reached 250–300 mg/100 mL, which is equivalent to the content of commercially available GABA supplements. The beverages received a positive rating (4/5) by the taste panel. To our knowledge, this is the first report on E. malodoratus as a potential GABA producer.

An Overview of Bioprocesses Employing Specifically Selected Microbial Catalysts for γ-Aminobutyric Acid Production

Gamma-aminobutyric acid (GABA) is an important chemical compound in the human brain. GABA acts as an inhibitory neurotransmitter by inducing hyperpolarization of cellular membranes. Usually, this pharmaceutically important compound is synthesized using a chemical process, but in this short overview we have only analysed microbial processes, which have been studied for the biosynthesis of this commercially important compound. The content of this article includes the following summarised information: the search for biological processes showed a number of lactic acid bacteria and certain species of fungi, which could be effectively used for the production of GABA. Strains found to possess GABA-producing pathways include Lactobacillus brevis CRL 1942, L. plantarum FNCC 260, Streptococcus salivarius subsp. thermophilus Y2, Bifidobacterium strains, Monascus spp., and Rhizopus spp. Each of these strains required specific growth conditions. However, several factors were common among these strains, such as the use of two main supplements in their fermentation medium—monosodium glutamate and pyridoxal phosphate—and maintaining an acidic pH. Optimization studies of GABA production were comprised of altering the media constituents, modifying growth conditions, types of cultivation system, and genetic manipulation. Some strains increased the production of GABA under anaerobic conditions. Genetic manipulation focused on silencing some genes or overexpression of gadB and gadC. The conclusion, based on the review of information available in published research, is that the targeted manipulation of selected microorganisms, as well as the culture conditions for an optimised bioprocess, should be adopted for an increased production of GABA to meet its increasing demand for food and pharmaceutical applications.

A Multi-strain Potential Probiotic Formulation of GABA-Producing Lactobacillus plantarum 90sk and Bifidobacterium adolescentis 150 with Antidepressant Effects

Today, a number of studies conclusively show that certain bacterial strains, mainly from the genera Lactobacillus and Bifidobacterium, influence the functioning of the central nervous system, leading to changes in beahvior, nociception and the cognitive abilities of humans and animals. Such strains serve as the basis for developing probiotics with a curative potential for the central nervous system - psychobioitcs. However, the question of how to find such strains and which criteria to use for their selection remains unanswered. Some compounds produced by bacteria, such as gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter of the central nervous system, are potential mediators between bacterial cells and the host. Previously, we established that some species of Lactobacillus and Bifidobacterium are capable of producing GABA. We presumed that GABA-producing Lactobacillus and Bifidobacterium strains are great candidates to use as psychobiotics. Therefore, we selected the strains Lactobacillus plantarum 90sk and Bifidobacterium adolescentis 150 as efficient GABA producers. The goal of this work was to assess the probiotic properties of the selected strains as well as their antidepressive effects in mice. We established that the ingestion of the probiotic composition based on the selected strains by BALB/c mice for 2 weeks reduced depressive-like behavior in the forced swimming test; the effect was similar to that of fluoxetine.

Optimization of gamma-aminobutyric acid production by Lactobacillus brevis PML1 in dairy sludge-based culture medium through response surface methodology

Gamma-aminobutyric acid (GABA) is a pharmaceutical, bioactive amino acid that can produce by some species of Lactic Acid Bacteria (LAB). For the first time, we evaluated the production of GABA by Lactobacillus brevis PML1 in the medium that contain the contaminant food bio-product like dairy sludge and soybean meal. GABA production was analyzed by chromatography (TLC, HPLC) and the features of fermented extract which contains this amino acid were evaluated. The results of Response Surface Methodology (RSM) of Central Composite Design (CCD) at p < .05 showed 300 ppm of GABA production in optimal treatment including 14.77% dairy sludge powder, 6.27% soybean meal, and 0.49% ammonium sulfate (32°C for 120 hr fermentation). The results of fermented extract also showed the acceptable antimicrobial, antioxidant, and toxicity (against cancer cell) properties. Also, L. brevis PML1has not shown any hemolytic or DNase activity which confirm its safety aspects. According to the results, this new culture can be used as a cheap substrate to biological production of GABA, by L. brevis PML1 in various food and pharmaceutical formulations.

Exploring the Role and Potential of Probiotics in the Field of Mental Health: Major Depressive Disorder

The field of probiotic has been exponentially expanding over the recent decades with a more therapeutic-centered research. Probiotics mediated microbiota modulation within the microbiota–gut–brain axis (MGBA) have been proven to be beneficial in various health domains through pre-clinical and clinical studies. In the context of mental health, although probiotic research is still in its infancy stage, the promising role and potential of probiotics in various mental disorders demonstrated via in-vivo and in-vitro studies have laid a strong foundation for translating preclinical models to humans. The exploration of the therapeutic role and potential of probiotics in major depressive disorder (MDD) is an extremely noteworthy field of research. The possible etio-pathological mechanisms of depression involving inflammation, neurotransmitters, the hypothalamic–pituitary–adrenal (HPA) axis and epigenetic mechanisms potentially benefit from probiotic intervention. Probiotics, both as an adjunct to antidepressants or a stand-alone intervention, have a beneficial role and potential in mitigating anti-depressive effects, and confers some advantages compared to conventional treatments of depression using anti-depressants.

Deep Transcranial Magnetic Stimulation Affects Gut Microbiota Composition in Obesity: Results of Randomized Clinical Trial

Growing evidence highlights the crucial role of gut microbiota in affecting different aspects of obesity. Considering the ability of deep transcranial magnetic stimulation (dTMS) to modulate the cortical excitability, the reward system, and, indirectly, the autonomic nervous system (ANS), we hypothesized a potential role of dTMS in affecting the brain-gut communication pathways, and the gut microbiota composition in obesity. In a hospital setting, 22 subjects with obesity (5 M, 17 F; 44.9 ± 2.2 years; BMI 37.5 ± 1.0 kg/m²) were randomized into three groups receiving 15 sessions (3 per week for 5 weeks) of high frequency (HF), low frequency (LF) dTMS, or sham stimulation. Fecal samples were collected at baseline and after 5 weeks of treatment. Total bacterial DNA was extracted from fecal samples using the QIAamp DNA Stool Mini Kit (Qiagen, Italy) and analyzed by a metagenomics approach (Ion Torrent Personal Genome Machine). After 5 weeks, a significant weight loss was found in HF (HF: −4.1 ± 0.8%, LF: −1.9 ± 0.8%, sham: −1.3 ± 0.6%, p = 0.042) compared to LF and sham groups, associated with a decrease in norepinephrine compared to baseline (HF: −61.5 ± 15.2%, p < 0.01; LF: −31.8 ± 17.1%, p < 0.05; sham: −35.8 ± 21.0%, p > 0.05). Furthermore, an increase in Faecalibacterium (+154.3% vs. baseline, p < 0.05) and Alistipes (+153.4% vs. baseline, p < 0.05) genera, and a significant decrease in Lactobacillus (−77.1% vs. baseline, p < 0.05) were found in HF. Faecalibacterium variations were not significant compared to baseline in the other two groups (LF: +106.6%, sham: +27.6%; p > 0.05) as well as Alistipes (LF: −54.9%, sham: −15.1%; p > 0.05) and Lactobacillus (LF: −26.0%, sham: +228.3%; p > 0.05) variations. Norepinephrine change significantly correlated with Bacteroides (r² = 0.734; p < 0.05), Eubacterium (r² = 0.734; p < 0.05), and Parasutterella (r² = 0.618; p < 0.05) abundance variations in HF. In conclusion, HF dTMS treatment revealed to be effective in modulating gut microbiota composition in subjects with obesity, reversing obesity-associated microbiota variations, and promoting bacterial species representative of healthy subjects with anti-inflammatory properties.

Role of the Intestinal Microbiome, Intestinal Barrier and Psychobiotics in Depression

The intestinal microbiota plays an important role in the pathophysiology of depression. As determined, the microbiota influences the shaping and modulation of the functioning of the gut-brain axis. The intestinal microbiota has a significant impact on processes related to neurotransmitter synthesis, the myelination of neurons in the prefrontal cortex, and is also involved in the development of the amygdala and hippocampus. Intestinal bacteria are also a source of vitamins, the deficiency of which is believed to be related to the response to antidepressant therapy and may lead to exacerbation of depressive symptoms. Additionally, it is known that, in periods of excessive activation of stress reactions, the immune system also plays an important role, negatively affecting the tightness of the intestinal barrier and intestinal microflora. In this review, we have summarized the role of the gut microbiota, its metabolites, and diet in susceptibility to depression. We also describe abnormalities in the functioning of the intestinal barrier caused by increased activity of the immune system in response to stressors. Moreover, the presented study discusses the role of psychobiotics in the prevention and treatment of depression through their influence on the intestinal barrier, immune processes, and functioning of the nervous system.

Evaluation of GABA Production and Probiotic Activities of Enterococcus faecium BS5

Gamma-aminobutyric acid (GABA) is a principal inhibitory neurotransmitter in the central nervous system and is produced by irreversible decarboxylation of glutamate. It possesses several physiological functions such as neurotransmission, diuretic, and tranquilizer effects and also regulates cardiovascular functions such as blood pressure and heart rate in addition to playing a role in the reduction of pain and anxiety. The objective of this study was to evaluate the GABA producing ability and probiotic capability of certain lactic acid bacteria strains isolated from dairy products. Around sixty-four bacterial isolates were collected and screened for their ability to produce GABA from monosodium glutamate, among which nine isolates were able to produce GABA. The most efficient GABA producer was Enterococcus faecium BS5. Further, assessment of several important and desirable probiotic properties showed that Ent. faecium BS5 was resistant to acid stress, bile salt, and antibiotics. Ent. faecium BS5 may potentially be used for large-scale industrial production of GABA and also for functional fermented product development.

Optimization and comparison of ℽ-aminobutyric acid (GABA) production by LAB in soymilk using RSM and ANN models

Background

ℽ-Aminobutyric acid (GABA) is a non-proteinaceous amino acid. In the mammalian nervous system, GABA functions as an inhibitory neurotransmitter. The present study focused on screening and optimization of ℽ-aminobutyric acid (GABA) yield by lactic acid bacteria by using soymilk as basal media. Lactobacillus fermentum (Lb. fermentum) was isolated from sourdough. The qualitative confirmation of GABA production by Lb. fermentum was observed by detecting colored spots on thin layer chromatography plate (TLC) and comparing it with standard GABA spot. The GABA from bacteria is confirmed by its molecular mass using mass spectrophotometry analysis (MS analysis). Single variable experiments were conducted for various physical and nutritional parameters, and determined the GABA content produced from Lb. fermentum, viable bacterial count, and pH of the fermented soymilk medium. Experimental data were authenticated by using response surface method (RSM) and artificial neural network (ANN) model.

Results

The results demonstrated that through single variable experiments, the yield of GABA and the viable bacterial cells increased in soymilk containing one percent of glucose, monosodium glutamate (MSG), and inoculum volume incubated at 37 °C, 48 h at pH 5. According to RSM results, the interaction of the highest concentration of MSG (1.5%) and mid glucose concentration (1.156%) yielded maximum GABA (5.54 g/L). The experimental data were in good agreement with two optimization models. The RSM models showed less error percentage than that of the ANN model.

Conclusion

This study indicates that soymilk is the best basal substrate for GABA production and growth of Lb. fermentum compared to synthetic media. Lb. fermentum can be explored further by food and pharmaceutical industries for the development of functional foods and therapeutic purposes.

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.

Health Benefits of Fermented Bamboo Shoots: The Twenty-First Century Green Gold of Northeast India

The word "bamboo" reminds us of "a hollow stick," but it is filled with a plethora of health benefits. The tribals of northeastern India ferment these beneficial bamboo shoots for the goodness of mankind. Fermentation is an important age-old biotechnological procedure used for the preservation of food products. Fermented bamboo shoots form the niche for many microorganisms, and this confers positive effects and advantages in many ways. These magical shoots have tremendous health benefits like anti-cancer, anti-oxidant, anti-aging, cardioprotective, weight loss, probiotics, to name a few. Apart from health benefits, fermented bamboo shoots form important functional foods and have industrial and economical values. Though these are commonly found and started in the tribal area, and local markets, today, they are valuable all around the world, as popular as gold. Hence, fermented bamboo shoots are referred as "green gold" of India. This review briefs about various health benefits, advantages, disadvantages, future scope, and finally the economic values of fermented bamboo shoots, the "green gold" of the twenty-first century.

The Microbiota-Gut-Brain Axis and Alzheimer's Disease: Neuroinflammation Is to Blame?

For years, it has been reported that Alzheimer’s disease (AD) is the most common cause of dementia. Various external and internal factors may contribute to the early onset of AD. This review highlights a contribution of the disturbances in the microbiota–gut–brain (MGB) axis to the development of AD. Alteration in the gut microbiota composition is determined by increase in the permeability of the gut barrier and immune cell activation, leading to impairment in the blood–brain barrier function that promotes neuroinflammation, neuronal loss, neural injury, and ultimately AD. Numerous studies have shown that the gut microbiota plays a crucial role in brain function and changes in the behavior of individuals and the formation of bacterial amyloids. Lipopolysaccharides and bacterial amyloids synthesized by the gut microbiota can trigger the immune cells residing in the brain and can activate the immune response leading to neuroinflammation. Growing experimental and clinical data indicate the prominent role of gut dysbiosis and microbiota–host interactions in AD. Modulation of the gut microbiota with antibiotics or probiotic supplementation may create new preventive and therapeutic options in AD. Accumulating evidences affirm that research on MGB involvement in AD is necessary for new treatment targets and therapies for AD.

Microbial Production and Enzymatic Biosynthesis of γ-Aminobutyric Acid (GABA) Using Lactobacillus plantarum FNCC 260 Isolated from Indonesian Fermented Foods

In the present study, we isolated and screened thirty strains of GABA (γ-aminobutyric acid)-producing lactic acid bacteria (LAB) from traditional Indonesian fermented foods. Two strains were able to convert monosodium glutamate (MSG) to GABA after 24 h of cultivation at 37 °C based on thin layer chromatography (TLC) screening. Proteomic identification and 16S rDNA sequencing using MALDI-TOF MS identified the strain as Lactobacillus plantarum designated as L. plantarum FNCC 260 and FNCC 343. The highest yield of GABA production obtained from the fermentation of L. plantarum FNCC 260 was 809.2 mg/L of culture medium after 60 h of cultivation. The supplementation of 0.6 mM pyridoxal 5’-phosphate (PLP) and 0.1 mM pyridoxine led to the increase in GABA production to 945.3 mg/L and 969.5 mg/L, respectively. The highest GABA production of 1226.5 mg/L of the culture medium was obtained with 100 mM initial concentration of MSG added in the cultivation medium. The open reading frame (ORF) of 1410 bp of the gadB gene from L. plantarum FNCC 260 encodes 469 amino acids with a calculated molecular mass of 53.57 kDa. The production of GABA via enzymatic conversion of monosodium glutamate (MSG) using purified recombinant glutamate decarboxylase (GAD) from L. plantarum FNCC 260 expressed in Escherichia coli was found to be more efficient (5-fold higher within 6 h) than the production obtained from fermentation. L. plantarum FNCC 260 could be of interest for the synthesis of GABA.

Psychobiotics: Mechanisms of Action, Evaluation Methods and Effectiveness in Applications with Food Products

The gut-brain-microbiota axis consists of a bilateral communication system that enables gut microbes to interact with the brain, and the latter with the gut. Gut bacteria influence behavior, and both depression and anxiety symptoms are directly associated with alterations in the microbiota. Psychobiotics are defined as probiotics that confer mental health benefits to the host when ingested in a particular quantity through interaction with commensal gut bacteria. The action mechanisms by which bacteria exert their psychobiotic potential has not been completely elucidated. However, it has been found that these bacteria provide their benefits mostly through the hypothalamic-pituitary-adrenal (HPA) axis, the immune response and inflammation, and through the production of neurohormones and neurotransmitters. This review aims to explore the different approaches to evaluate the psychobiotic potential of several bacterial strains and fermented products. The reviewed literature suggests that the consumption of psychobiotics could be considered as a viable option to both look after and restore mental health, without undesired secondary effects, and presenting a lower risk of allergies and less dependence compared to psychotropic drugs.

Glutamate Decarboxylase from Lactic Acid Bacteria-A Key Enzyme in GABA Synthesis

Glutamate decarboxylase (l-glutamate-1-carboxylase, GAD; EC 4.1.1.15) is a pyridoxal-5’-phosphate-dependent enzyme that catalyzes the irreversible α-decarboxylation of l-glutamic acid to γ-aminobutyric acid (GABA) and CO₂. The enzyme is widely distributed in eukaryotes as well as prokaryotes, where it—together with its reaction product GABA—fulfils very different physiological functions. The occurrence of gad genes encoding GAD has been shown for many microorganisms, and GABA-producing lactic acid bacteria (LAB) have been a focus of research during recent years. A wide range of traditional foods produced by fermentation based on LAB offer the potential of providing new functional food products enriched with GABA that may offer certain health-benefits. Different GAD enzymes and genes from several strains of LAB have been isolated and characterized recently. GABA-producing LAB, the biochemical properties of their GAD enzymes, and possible applications are reviewed here.

γ-Aminobutyric acid found in fermented foods and beverages: current trends

γ-aminobutyric acid (GABA) is synthesised by glutamic acid decarboxylase which catalyses the decarboxylation of L-glutamic acid. L-glutamic acid is formed by α-ketoglutarate in the TCA cycle by glutamic acid dehydrogenase (GDH). GABA is found in the human brain, plants, animals and microorganisms. GABA functions as an antidepressant, antihypertensive, antidiabetic and immune system enhancer and has a good effect on neural disease. As GABA have pharmaceutical properties, conditions for GABA production need to be established. Microbiological GABA production is more safe and eco-friendly rather than chemical methods. Moreover, it is easier to control conditions of production using microorganisms compared to production in plants and animals. GABA production in fermented foods and beverages has the potential to be optimised to increase the functional effect of fermented foods and beverages.

Human Gut-Microbiota Interaction in Neurodegenerative Disorders and Current Engineered Tools for Its Modeling

The steady increase in life-expectancy of world population, coupled to many genetic and environmental factors (for instance, pre- and post-natal exposures to environmental neurotoxins), predispose to the onset of neurodegenerative diseases, whose prevalence is expected to increase dramatically in the next years. Recent studies have proposed links between the gut microbiota and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Human body is a complex structure where bacterial and human cells are almost equal in numbers, and most microbes are metabolically active in the gut, where they potentially influence other target organs, including the brain. The role of gut microbiota in the development and pathophysiology of the human brain is an area of growing interest for the scientific community. Several microbial-derived neurochemicals involved in the gut-microbiota-brain crosstalk seem implicated in the biological and physiological basis of neurodevelopment and neurodegeneration. Evidence supporting these connections has come from model systems, but there are still unsolved issues due to several limitations of available research tools. New technologies are recently born to help understanding the causative role of gut microbes in neurodegeneration. This review aims to make an overview of recent advances in the study of the microbiota-gut-brain axis in the field of neurodegenerative disorders by: (a) identifying specific microbial pathological signaling pathways; (b) characterizing new, advanced engineered tools to study the interactions between human cells and gut bacteria.

Evaluation of Antiobesity Activity of Soybean Meal Products Fermented by Lactobacillus plantarum FPS 2520 and Bacillus subtilis N1 in Rats Fed with High-Fat Diet

Single strain or mixed strains of Lactobacillus plantarum FPS 2520 and Bacillus subtilis N1 were used to ferment soybean meal (SBM), and the antiobesity activity of the fermented SBM product was investigated in rats fed with high-fat diet (HFD). After fermentation, free amino nitrogen, total peptide, and isoflavone contents were markedly raised, and genistein and daidzein were the major isoflavones in the fermented SBM. After fed with HFD for 10 weeks, obese Sprague-Dawley rats were orally treated with various fermented products for 6 weeks. The body weight gains, as well as weights of abdominal fat and epididymis fat, of rats fed with fermented SBM products were significantly downregulated. The treatment with the mixed-strains fermented SBM product significantly decreased plasma levels of triglyceride (TG), total cholesterol (TC), and low-density lipoprotein-cholesterol, but increased the level of high-density lipoprotein-cholesterol. Moreover, the levels of TG, TC, fatty acid synthase, and acetyl-CoA carboxylase (ACC) in liver were diminished, and the activities of hormone-sensitive lipase and lipoprotein lipase in adipose tissue were augmented. Taken together, these data demonstrated the antiobesity activity of fermented SBM products, among which the product fermented by the mixed strains being the most effective one. Therefore, these fermented SBM products are potential to be developed as functional foods or additives for treatment of obesity and prevention against obesity-induced complications.

Antidepressive Mechanisms of Probiotics and Their Therapeutic Potential

The accumulating knowledge of the host-microbiota interplay gives rise to the microbiota-gut-brain (MGB) axis. The MGB axis depicts the interkingdom communication between the gut microbiota and the brain. This communication process involves the endocrine, immune and neurotransmitters systems. Dysfunction of these systems, along with the presence of gut dysbiosis, have been detected among clinically depressed patients. This implicates the involvement of a maladaptive MGB axis in the pathophysiology of depression. Depression refers to symptoms that characterize major depressive disorder (MDD), a mood disorder with a disease burden that rivals that of heart diseases. The use of probiotics to treat depression has gained attention in recent years, as evidenced by increasing numbers of animal and human studies that have supported the antidepressive efficacy of probiotics. Physiological changes observed in these studies allow for the elucidation of probiotics antidepressive mechanisms, which ultimately aim to restore proper functioning of the MGB axis. However, the understanding of mechanisms does not yet complete the endeavor in applying probiotics to treat MDD. Other challenges remain which include the heterogeneous nature of both the gut microbiota composition and depressive symptoms in the clinical setting. Nevertheless, probiotics offer some advantages over standard pharmaceutical antidepressants, in terms of residual symptoms, side effects and stigma involved. This review outlines antidepressive mechanisms of probiotics based on the currently available literature and discusses therapeutic potentials of probiotics for depression.

A Brief Review on the Non-protein Amino Acid, Gamma-amino Butyric Acid (GABA): Its Production and Role in Microbes

Gamma-Aminobutyric acid (GABA) is a non-protein amino acid widely distributed in nature. It is produced through irreversible α-decarboxylation of glutamate by enzyme glutamate decarboxylase (GAD). GABA and GAD have been found in plants, animals, and microorganisms. GABA is distributed throughout the human body and it is involved in the regulation of cardiovascular conditions such as blood pressure and heart rate, and plays a role in the reduction of anxiety and pain. Although researchers had produced GABA by chemical method earlier it became less acceptable as it pollutes the environment. Researchers now use a more promising microbial method for the production of GABA. In the drug and food industry, demand for GABA is immense. So, large scale conversion of GABA by microbes has got much attention. So this review focuses on the isolation source, production, and functions of GABA in the microbial system. We also summarize the mechanism of action of GABA and its shunt pathway.

The Gut Microbiota Links Dietary Polyphenols With Management of Psychiatric Mood Disorders

The pathophysiology of depression is multifactorial yet generally aggravated by stress and its associated physiological consequences. To effectively treat these diverse risk factors, a broad acting strategy is required and is has been suggested that gut-brain-axis signaling may play a pinnacle role in promoting resilience to several of these stress-induced changes including pathogenic load, inflammation, HPA-axis activation, oxidative stress and neurotransmitter imbalances. The gut microbiota also manages the bioaccessibility of phenolic metabolites from dietary polyphenols whose multiple beneficial properties have known therapeutic efficacy against depression. Although several potential therapeutic mechanisms of dietary polyphenols toward establishing cognitive resilience to neuropsychiatric disorders have been established, only a handful of studies have systematically identified how the interaction of the gut microbiota with dietary polyphenols can synergistically alleviate the biological signatures of depression. The current review investigates several of these potential mechanisms and how synbiotics, that combine probiotics with dietary polyphenols, may provide a novel therapeutic strategy for depression. In particular, synbiotics have the potential to alleviate neuroinflammation by modulating microglial and inflammasome activation, reduce oxidative stress and balance serotonin metabolism therefore simultaneously targeting several of the major pathological risk factors of depression. Overall, synbiotics may act as a novel therapeutic paradigm for neuropsychiatric disorders and further understanding the fundamental mechanisms of gut-brain-axis signaling will allow full utilization of the gut microbiota's as a therapeutic tool.