Heterologous production of equol by lactic acid bacteria strains in culture medium and food

Advances in the Metabolic Mechanism and Functional Characteristics of Equol

Equol is the most potent soy isoflavone metabolite and is produced by specific intestinal microorganisms of mammals. It has promising application possibilities for preventing chronic diseases such as cardiovascular disease, breast cancer, and prostate cancer due to its high antioxidant activity and hormone-like activity. Thus, it is of great significance to systematically study the efficient preparation method of equol and its functional activity. This paper elaborates on the metabolic mechanism of equol in humans; focuses on the biological characteristics, synthesis methods, and the currently isolated equol-producing bacteria; and looks forward to its future development and application direction, aiming to provide guidance for the application and promotion of equol in the field of food and health products.

Isoflavone Metabolism by Lactic Acid Bacteria and Its Application in the Development of Fermented Soy Food with Beneficial Effects on Human Health

Isoflavones are phenolic compounds (considered as phytoestrogens) with estrogenic and antioxidant function, which are highly beneficial for human health, especially in the aged population. However, isoflavones in foods are not bioavailable and, therefore, have low biological activity. Additionally, their transformation into bioactive compounds by microorganisms is necessary to obtain bioavailable isoflavones with beneficial effects on human health. Many lactic acid bacteria (LAB) can transform the methylated and glycosylated forms of isoflavones naturally present in foods into more bioavailable aglycones, such as daidzein, genistein and glycitein. In addition, certain LAB strains are capable of transforming isoflavone aglycones into compounds with a greater biological activity, such as dihydrodaidzein (DHD), O-desmethylangolensin (O-DMA), dihydrogenistein (DHG) and 6-hydroxy-O-desmethylangolensin (6-OH-O-DMA). Moreover, Lactococcus garviae 20-92 is able to produce equol. Another strategy in the bioconversion of isoflavones is the heterologous expression of genes from Slackia isoflavoniconvertens DSM22006, which have allowed the production of DHD, DHG, equol and 5-hydroxy-equol in high concentrations by engineered LAB strains. Accordingly, the consequences of isoflavone metabolism by LAB and its application in the development of foods enriched in bioactive isoflavones, as well as health benefits attributed to their consumption, will be addressed in this work.

Assessment of short-read shotgun sequencing and microbiome analysis of faecal samples to discriminate between equol producers and non-producers

Among the isoflavones and isoflavone-derived metabolites, equol, which in the human gut is synthesised from daidzein by minority bacterial populations, shows the strongest estrogenic and antioxidant activity. The beneficial effects on human health of isoflavone consumption might be partially or indeed totally attributable to this equol. Although some of the bacterial strains involved in its formation have been identified, the interplay between the composition and functionality of the gut microbiota and equol producer phenotype has hardly been studied. In this study, after shotgun metagenomic sequencing, different pipelines for the taxonomic and functional annotation of sequencing data were used in the search for similarities and differences in the faecal metagenome of equol-producing (n=3) and non-producing (n=2) women, with special focus on equol-producing taxa and their equol-associated genes. The taxonomic profiles of the samples differed significantly depending on the analytical method followed, although the microbial diversity detected by each tool was very similar at the phylum, genus and species levels. Equol-producing taxa were detected in both equol producers and non-producers, but no correlation between the abundance of equol-producing taxa and the equol producing/non-producing phenotype was found. Indeed, functional metagenomic analysis was unable to identify the genes involved in equol production, even in samples from equol producers. By aligning equol operons with the collected metagenomics data, a small number of reads mapping to equol-associated sequences were recognised in samples from both equol producers and equol non-producers, but only two reads mapping onto equol reductase-encoding genes in a sample from an equol producer. In conclusion, the taxonomic analysis of metagenomic data might not be suitable for detecting and quantifying equol-producing microbes in human faeces. Functional analysis of the data might provide an alternative. However, to detect the genetic makeup of the minority gut populations, more extensive sequencing than that achieved in the present study might be required.

The Interaction between Flavonoids and Intestinal Microbes: A Review

In recent years, research on the interaction between flavonoids and intestinal microbes have prompted a rash of food science, nutriology and biomedicine, complying with future research trends. The gut microbiota plays an essential role in the maintenance of intestinal homeostasis and human health, but once the intestinal flora dysregulation occurs, it may contribute to various diseases. Flavonoids have shown a variety of physiological activities, and are metabolized or biotransformed by gut microbiota, thereby producing new metabolites that promote human health by modulating the composition and structure of intestinal flora. Herein, this review demonstrates the key notion of flavonoids as well as intestinal microbiota and dysbiosis, aiming to provide a comprehensive understanding about how flavonoids regulate the diseases by gut microbiota. Emphasis is placed on the microbiota-flavonoid bidirectional interaction that affects the metabolic fate of flavonoids and their metabolites, thereby influencing their metabolic mechanism, biotransformation, bioavailability and bioactivity. Potentially by focusing on the abundance and diversity of gut microbiota as well as their metabolites such as bile acids, we discuss the influence mechanism of flavonoids on intestinal microbiota by protecting the intestinal barrier function and immune system. Additionally, the microbiota-flavonoid bidirectional interaction plays a crucial role in regulating various diseases. We explain the underlying regulation mechanism of several typical diseases including gastrointestinal diseases, obesity, diabetes and cancer, aiming to provide a theoretical basis and guideline for the promotion of gastrointestinal health as well as the treatment of diseases.

Soy isoflavone-specific biotransformation product S-equol in the colon: physiological functions, transformation mechanisms, and metabolic regulatory pathways

Epidemiological data suggest that regular intake of soy isoflavones may reduce the incidence of estrogen-dependent and aging-associated disorders. Equol is a metabolite of soy isoflavone (SI) produced by specific gut microbiota and has many beneficial effects on human health due to its higher biological activity compared to SI. However, only 1/3 to 1/2 of humans are able to produce equol in the body, which means that not many people can fully benefit from SI. This review summarizes the recent advances in equol research, focusing on the chemical properties, physiological functions, conversion mechanisms in vitro and vivo, and metabolic regulatory pathways affecting S-equol production. Advanced experimental designs and possible techniques in future research plan are also fully discussed. Furthermore, this review provides a fundamental basis for researchers in the field to understand individual differences in S-equol production, the efficiency of metabolic conversion of S-equol, and fermentation production of S-equol in vitro.

Fermentation of soymilk by Lactobacillus acidipiscis isolated from Chinese stinky tofu capable of efficiently biotransforming isoflavone glucosides to dihydrodaidzein and dihydrogenistein

BACKGROUND

The soy isoflavone microbial metabolites dihydrodaidzein (DHD), dihydrogenistein (DHG), equol and 5-hydroxy-equol are generally more biologically active than their precursors daidzein and genistein. Bacteria responsible for isoflavone metabolism have been isolated and identified. Fermented soymilk is a potential functional food; however, there are few lactic acid bacteria capable of metabolizing soy isoflavones.

RESULTS

A newly isolated Gram-positive facultative anaerobic bacterium, which was named Lactobacillus acidipiscis HAU-FR7, was isolated from the traditional Chinese fermented soy product 'stinky tofu'. Bacterium strain HAU-FR7 can grow under aerobic conditions and can also convert most of the daidzin and genistin in soymilk into DHD and DHG, respectively. The concentrations of DHD and DHG produced were 183 and 134 μmol L^-1 , respectively, after fermentation for 24 h. Strain HAU-FR7 does not produce the biogenic amines cadaverine, putrescine, histamine or tyramine, and an antibiotic susceptibility test showed that HAU-FR7 is sensitive to nine of the ten tested antibiotics, except for vancomycin. Moreover, the 1,1-diphenyl-2- picrylhydrazyl free radical scavenging capacity of soymilk fermented with HAU-FR7 was significantly higher than that of unfermented soymilk.

CONCLUSION

A facultative anaerobic lactic acid bacterium, designated Lactobacillus acidipiscis HAU-FR7, is capable of reducing the soy isoflavone glucosides daidzin and genistin in soymilk to DHD and DHG efficiently, even in the presence of atmospheric oxygen. The biotransformation activity of HAU-FR7 grown in soymilk is higher than that in de Man-Rogosa-Sharpe liquid culture medium. © 2022 Society of Chemical Industry.

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.

Maximizing the Estrogenic Potential of Soy Isoflavones through the Gut Microbiome: Implication for Cardiometabolic Health in Postmenopausal Women

Soy isoflavones have been suggested as an alternative treatment for managing postmenopausal symptoms and promoting long-term health due to their structural similarity to mammalian estrogen and ability to bind to estrogen receptors. Among all soy isoflavones and their metabolites, (S)-equol is known for having the strongest estrogenic activity. Equol is a metabolite of the soy isoflavone daidzein produced through intestinal bacterial metabolism. However, more than half of the human population is not able to produce equol due to the lack of equol-producing bacteria in their gastrointestinal tract. The interpersonal variations in the gut microbiome complicate the interpretation of data collected from humans. Furthermore, because rodents are efficient equol-producers, translatability between rodent models and humans is challenging. Herein, we first summarized the current knowledge of the microbial conversion of daidzein to equol, its relation to health, and proposed the need for developing model systems by which equol production can be manipulated while controlling other known confounding factors. Determining the necessity of equol-producing capacity within a gut microbial community when consuming soy as a functional ingredient, and identifying strategies to maximize equol production by modulating the gut microbiome, may provide future therapeutic approaches to improve the health of postmenopausal women.

Strategies to achieve significant physiological concentrations of bioactive phytoestrogens in plasma

The benefits to health attributed to the intake of phytoestrogens (PEs) have been demonstrated in previous studies with significant physiological concentrations of bioactive PEs, such as genistein, equol, enterolignans and urolithins in plasma. However, the achievement of high bioactive PE levels in plasma is restricted to a select population group, mainly due to the low intake of plant PEs and/or the absence, or inhibition, of the microbiota capable of producing these bioactive forms. In this study, the intake of plant PEs, the concentration of bioactive PEs in plasma, the ability of the intestinal microbiota to produce bioactive PEs, as well as the different mechanisms used by GRAS bacteria to increase the level of bioactive PEs were evaluated concluding that the use of GRAS bacteria bioactive PE producers and the development of fermented foods enriched in bioactive PEs in addition to a high intake of plant PEs and taking care of the intestinal microbiota, are some of the different strategies to achieve significant physiological concentrations of bioactive PEs in the intestine and, subsequently, in plasma and targets organs which are essential to improve menopausal symptoms or reduce the risk of some pathologies such as breast and colon cancer, or cardiovascular disease.