Effects of Red-Bean Tempeh with Various Strains of Rhizopus on GABA Content and Cortisol Level in Zebrafish

Fermented foods: Harnessing their potential to modulate the microbiota-gut-brain axis for mental health

Over the past two decades, whole food supplementation strategies have been leveraged to target mental health. In addition, there has been increasing attention on the ability of gut microbes, so called psychobiotics, to positively impact behaviour though the microbiota-gut-brain axis. Fermented foods offer themselves as a combined whole food microbiota modulating intervention. Indeed, they contain potentially beneficial microbes, microbial metabolites and other bioactives, which are being harnessed to target the microbiota-gut-brain axis for positive benefits. This review highlights the diverse nature of fermented foods in terms of the raw materials used and type of fermentation employed, and summarises their potential to shape composition of the gut microbiota, the gut to brain communication pathways including the immune system and, ultimately, modulate the microbiota-gut-brain axis. Throughout, we identify knowledge gaps and challenges faced in designing human studies for investigating the mental health-promoting potential of individual fermented foods or components thereof. Importantly, we also suggest solutions that can advance understanding of the therapeutic merit of fermented foods to modulate the microbiota-gut-brain axis.

Optimization of the hongqu starter preparation process for the manufacturing of red mold rice with high gamma-aminobutyric acid production by solid-state fermentation

Red mold rice (RMR) generally contains gamma-aminobutyric acid (GABA), which has several physiological functions. Monascus purpureus M162, with a high GABA production of 15.10 mg/g was generated by atmospheric and room temperature plasma mutation. Furthermore, we conducted a response surface methodology to produce a premium hongqu starter. The results revealed that under optimal conditions, that is, a substrate containing brown rice and bran in a brown rice: bran ratio of 9:1 (wt/wt), an inoculation size of 21.50 mL/100 g, a mixing frequency of one time/9 h, and a cultivation time of 7.20 days, the number of active spores, α-amylase activity, and saccharification power activity was 4.15 × 10⁷ spores/g, 155 U/g, and 3260 U/g in the high-quality starter, respectively. These values were 224.32-fold, 139.64%, and 141.74% higher than those obtained with M. purpureus M162 inoculated into steamed indica rice, respectively, and 153.70-fold, 267.24%, and 151.63% higher than those obtained with the parent strain M. purpureus M1, respectively. The premium hongqu starter of M. purpureus M162 was inoculated into steamed indica rice to produce RMR with 15.93 mg/g of GABA. In conclusion, we proposed a novel strategy for functional RMR production with high GABA concentrations by solid-state fermentation with Monascus spp.

Effect of Tempeh on Gut Microbiota and Anti-Stress Activity in Zebrafish

Rhizopus oryzae is a fungus used to ferment tempeh in Indonesia and is generally recognized as safe (GRAS) for human consumption by the USA FDA. We previously assessed the effect of a tempeh extract on cortisol levels in zebrafish but did not include behavioral studies. Here, we measured the GABA content in three strains of Rhizopus oryzae, two isolated by us (MHU 001 and MHU 002) and one purchased. We then investigated the effect of tempeh on cortisol and the gut microbiota in a zebrafish experimental model. GABA concentration was the highest in MHU 002 (9.712 ± 0.404 g kg⁻¹) followed by our MHU 001 strain and the purchased one. The fish were divided into one control group fed a normal diet and three experimental groups fed soybean tempeh fermented with one of the three strains of Rhizopus oryzae. After two weeks, individual fish were subjected to unpredicted chronic stress using the novel tank diving test and the tank light–dark test. Next-generation sequencing was used to analyze gut microbial communities and RT-PCR to analyze the expression of BDNF (brain-derived neurotrophic factor) gene and of other genes involved in serotonin signaling/metabolism in gut and brain. Tempeh-fed zebrafish exhibited increased exploratory behavior (less stress) in both tank tests. They also had significantly reduced gut Proteobacteria (include E. coli) (51.90% vs. 84.97%) and significantly increased gut Actinobacteria (include Bifidobacterium spp.) (1.80% vs. 0.79%). The content of Bifidobacteriumadolescentis, a “psychobiotic”, increased ten-fold from 0.04% to 0.45%. Tempeh also increases BDNF levels in zebrafish brain. Rhizopus oryzae MHU 001 greatly improved the anti-stress effect of tempeh and microbiota composition in zebrafish gut.

Introducing Tempeh as a New Plant-Based Protein Food Item on the Danish Market

Decreasing meat consumption has resulted in a need for new high-quality protein sources. Tempeh is relatively unknown in Denmark and might be capable of meeting this need. The aim of the study was to describe the success criteria for introducing locally produced tempeh and to investigate the sensory quality of three types of tempeh. Only 24% of the consumers in the survey (n = 395) used meat alternatives, which might be explained by a low level of satisfaction with availability. Tempeh was known by 26%—the less meat eaten, the greater the knowledge of tempeh. Twenty-three per cent of the consumers had positive attitudes towards tempeh. The three types of tempeh had markedly different sensory profiles. Nevertheless, the home use test showed that they could be used interchangeably in different recipes. In addition, the consumers were more positive about recipes in which tempeh did not resemble meat compared with meat-inspired recipes. In conclusion, introducing locally produced tempeh on the Danish market is possible but would require further knowledge of the product. In addition, tempeh should be sold as a tasty, high-quality protein food item in its own right. Recipes using tempeh should reflect this and not mimic meat recipes.