Discovery of novel prebiotic effects of yeast mannan
〜Selectively increases specific healthy gut bacteria without affecting the diversity of intestinal flora〜
In recent years, awareness of the gut as a source of health has been growing, with terms like “chokatsu (intestinal function)” and “intestinal flora”1 becoming mainstream. Now, research by Asahi has found that yeast mannan2, a type of dietary fiber contained in the yeast cell wall , promotes healthy gut bacteria and has the potential to improve intestinal health. Yeast mannan could play a key role as an option for improving health in the future. Here we present an overview of yeast mannan, as discovered in this research.
●It was found that yeast mannan selectively promotes specific intestinal bacteria, Bacteroides thetaiotaomicron3 and Bacteroides ovatus, without affecting the diversity of intestinal flora.
●It was found that yeast mannan augments short-chain fatty acids4 that are vital to the maintenance of human health.
●Yeast mannan is a novel prebiotic5 with potential applications in improving intestinal health.
Shunsuke Oba, Core Technology Laboratories, Asahi Quality & Innovations, Ltd.
“Yeast has been used in a wide range of fermented foods and beverages, such as bread, beer, and wine. So the image of yeast is strongly ingrained as creating flavor through fermentation. In fact, Asahi Group has been researching the health functions of yeast for many years. In this study, we were able to report the benefits of novel prebiotic effects through yeast mannan. It is also a good way of using up recovered brewer’s yeast, a byproduct of the beer brewing process. I would be delighted if the value of yeast, which is able to contribute to human health and the development of the circular economy, were to be recognized the world over.”
Daisuke Sasaki, Assistant Professor, Department of Science, Technology and Innovation, Graduate School of Science, Technology and Innovation, Kobe University
The Kobe University Human Intestinal Microbiota Model (KUHIMM)6 is able to closely replicate the volume and species of microbes in the large intestine, as well as metabolites. By replicating the flora in particular, the team has been able to reproduce the interaction and symbiosis that takes place in the large intestine, such as the metabolic cross-feeding among microbes. In this study, an evaluation using the model found that yeast mannan promoted specific intestinal microbes that are useful for human health. They also demonstrated its utility as a prebiotic. In an age when people are increasingly aware of the importance of a healthy gut to our overall health and well-being, I can only hope that research on yeast mannan and other prebiotics gathers pace so that people can enjoy health benefits from their intestines.
As an approach to maintaining the health of intestinal flora, there has been increasing focus in recent years on prebiotics, food compounds that induce the growth of beneficial microorganisms in the gastrointestinal tract, like oligosaccharides – which act to aid the propagation of bacteria such as lactic acid bacteria and bifidobacteria.
As a result of research to date on yeast mannan, we know that it has a range of functions related to improved intestinal health. However, what was not known was how yeast mannan acts within the human intestine. In this study, the Human Intestinal Microbiota Model developed by Kobe University was used to investigate the effects of yeast mannan on intestinal flora. The team made a pioneering discovery: that yeast mannan selectively promotes two healthy gut bacteria, B. thetaiotaomicron and B. ovatus at the species level7 without affecting the diversity of intestinal flora. They also found that it augments short-chain fatty acids, which have also been in the spotlight in recent years. These findings suggest that yeast mannan could be used as a novel prebiotic to improve intestinal health.
Fecal samples were taken from eight healthy subjects in their 30s to 40s who had not taken antibiotics during the last two months. Using the KUHIMM, each of the fecal samples was cultured for 30 hours with and without yeast mannan added. The DNA of intestinal microbes was extracted from the fecal samples and the samples after culturing, then the flora was analyzed using next-generation sequencing (NGS) and real-time PCR of 16S rRNA gene data. High-performance liquid chromatography (HPLC) was also used to gauge the concentration of short-chain fatty acids in the cultured samples.
Fig. 1. The genus-level composition of intestinal bacteria (*created with reference to the paper)
This chart uses colors to display the relative abundance of bacteria genera among intestinal flora.
No statistically significant difference was found between the microbial composition of samples with YM and without YM (CUL).
The genus-level composition of bacteria was compared among fecal samples from eight healthy subjects (referred to as FEC), and the control culture without yeast mannan prepared (CUL) and the cultured samples with yeast mannan (YM) using the KUHIMM. No statistically significant difference was found between the microbial composition of CUL and YM. YM administration did not alter the overall bacterial genus‑level composition, confirming that it did not affect the diversity of intestinal flora (Fig. 1).
Fig. 2. Relative abundance of genus Bacteroides
After the culturing of the fecal samples for 30 hours in the KUHIMM model, significant increase in only two species of Bacteroides – a dominant bacterial genus in the gut – was found, B. thetaiotaomicron and B. ovatus (Fig. 2). Four other microbes of the genus Bacteroides did not show any increase as a result of the addition of yeast mannan.
Fig. 3. (a) short-chain fatty acids concentration and (b) pH in CUL and YM
After the culturing of the fecal samples for 30 hours in the KUHIMM model, the concentrations of acetate, propionate, and total short-chain fatty acids (SCFAs), which are useful for human health, were significantly higher in the YM samples than in the CUL samples (Fig. 3a). The pH level of the samples with YM was also lower than the CUL samples (Fig. 3b).
Fig. 4. The correlation between the relative ratio of Bacteroides thetaiotaomicron
and Bacteroides ovatus (with yeast mannan / without yeast mannan [CUL]).
After the culturing of the fecal samples for 30 hours in the KUHIMM model, a comparison of relative abundance of B. thetaiotaomicron and B. ovatus (in the YM group relative to the control group) found a strong positive correlation. This suggests that the two microbe types metabolize YM in a coordinated manner, the growth of one assisting the growth of the other.
From this study, it is clear that yeast mannan, a dietary fiber found in yeast cell wall, promotes the growth of intestinal microbes beneficial to human health. Consumption of yeast mannan in human clinical trials has also found that (1) it increases the relative abundance of B. thetaiotaomicron and B. ovatus in the gut, (2) it suppresses production of indole and skatole, intestinal metabolites known for their toxicity, (3) it elevates level of equol, an intestinal metabolite beneficial to health and (4) it is a prebiotic that can be used to treat skin conditions such as dryness (*1 R. Tanihiro et al., 2020). In future, we hope to continue this research and harness yeast mannan as a prebiotic.
This study was undertaken together with Associate Professor Kengo Sasaki and Assistant Professor Daisuke Sasaki, Graduate School of Science, Technology and Innovation, Department of Science, Technology and Innovation at Kobe University, the core technology laboratory for Asahi Quality & Innovations, Ltd. (Headquarters: Ibaraki, Representative Director: Manabu Sami), which handles cutting-edge research for Asahi Group Holdings, Ltd. (Headquarters: Tokyo, CEO: Atsushi Katsuki). These research findings were published in the international science journal Scientific Reports on October 15, 2020. Asahi Quality & Innovations will continue to support the health of our customers through “R&D aiming to offer high-quality healthy ingredients.”
*1 Intestinal flora
The diverse bacteria that exist in the intestines of people and animals. Within the gut, the walls of the intestines are lined with microbes, such that they are comparable to a population of plants – hence the name intestinal flora.
*2 Yeast mannan
A type of dietary fiber contained in the yeast cell wall. Reported benefits to date are that it boosts immunity, promotes absorption of minerals, improves intestinal health, and promotes the elimination of cholesterol.
*3 Bacteroides thetaiotaomicron
A microbe of the genus Bacteroides. One of the most commonly microbes presented in human intestinal flora. Known for a variety of healthy functions such as preventing rotavirus infection and relieving colonic inflammation.
*4 Short-chain fatty acids
Organic acids produced by intestinal bacteria of up to six carbon atoms, such as acetate, propionate, and butyrate . They are produced in the colon by bacterial fermentation of dietary fibers. By creating a weakly acidic environment in the gut, they are believed to contribute to hampering the propagation of harmful microbes, promoting peristalsis and controlling immune response.
*5 Prebiotics
Food compounds that improve the health of the host by inducing the growth of or changing the activity of beneficial microorganisms in the gastrointestinal tract, or having a beneficial impact on the host.
*6 The Kobe University Human Intestinal Microbiota Model (KUHIMM)
This model developed at Kobe University is able to closely replicate the human intestinal flora. It also enables analysis of metabolic conversion of compounds entered into the model, changes in the relative abundance of gut microbiota, metabolites and more.
*7 At the species level
Species is the lowest level of biological classification of living things. Based on genomic information, this study is novel in that it explains the reasons for the selective increase in two species of microbe when yeast mannan is present.
