Brewers' spent grain (BSG) is the most abundant by-product of brewing. Due to its microbiological instability and high perishability, fresh BSG is currently disposed of as low-cost cattle feed. However, BSG is an appealing source of nutrients to obtain products with high added value through microbial-based transformation. As such, BSG could become a potential source of income for the brewery itself. While recent studies have covered the relevance of BSG chemical composition in detail, this review aims to underline the importance of microorganisms from the stabilization/contamination of fresh BSG to its biotechnological exploitation. Indeed, the evaluation of BSG-associated microorganisms, which include yeast, fungi, and bacteria, can allow their safe use and the best methods for their exploitation. This bibliographical examination is particularly focused on the role of microorganisms in BSG exploitation to (1) produce enzymes and metabolites of industrial interest, (2) supplement human and animal diets, and (3) improve soil fertility. Emerging safety issues in the use of BSG as a food and feed additive is also considered, particularly considering the presence of mycotoxins.Key points• Microorganisms are used to enhance brewers' spent grain nutritional value.• Knowledge of brewers' spent grain microbiota allows the reduction of health risks. Graphical abstract.

/pdf/the-role-of-microorganisms-on-biotransformation-of-brewers-36rezr3lto.pdf

The role of microorganisms on biotransformation of brewers' spent grain.

Medicinal mushrooms have documented effects against different diseases, including infections and inflammatory disorders. The related Basidiomycota Agaricus blazei Murill (AbM), Hericium erinaceus (HE), and Grifola frondosa (GF) have been shown to exert antimicrobial activity against viral agents, Gram-positive and Gram-negative bacteria, and parasites in vitro and in vivo. Since the mechanism is immunomodulatory and not antibiotical, the mushrooms should be active against multi-drug resistant microbes as well. Moreover, since these Basidiomycota also have anti-inflammatory properties, they may be suited for treatment of the severe lung inflammation that often follows COVID-19 infection. An AbM-based mushroom extract (Andosan™), also containing HE and GF, has been shown to significantly reduce bacteraemia and increase survival in mice with pneumococcal sepsis, and to improve symptoms and quality of life in IBD patients via an anti-inflammatory effect. Hence, such mushroom extracts could have prophylactic or therapeutic effect against the pneumonic superinfection and severe lung inflammation that often complicates COVID-19 infection. Here, we review antimicrobial and anti-inflammatory properties of AbM, HE and GF mushrooms, which could be used for the battle against COVID-19.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/sji.12937

Can medicinal mushrooms have prophylactic or therapeutic effect against COVID-19 and its pneumonic superinfection and complicating inflammation?

The nutritional properties of brewers' spent grain (BSG) have been widely studied, considering its potential as a healthy food ingredient. Because of its fiber composition (amount and ratio), however, adding BSG into the food matrix to bring about changes in physical properties has been believed to impact negatively on the acceptability of the final products' properties, particularly color and texture. Fiber modification can enhance the quality of fiber and can be applied to BSG. Although it appears challenging, modifying fiber composition requires further study, particularly if the acceptability of the final products is to be improved. Furthermore, the level of fiber degradation during the modification treatment needs to be examined to meet the increased demand for BSG in final food products. This concise synthesis provides a new perspective for increasing the use of BSG as a food ingredient that is characterized by high nutrition and acceptability.

Brewers' spent grain in food systems: Processing and final products quality as a function of fiber modification treatment.

The brewing industry is characterized by the large production of by-products. Following the fundamentals of a circular economy, several attempts to recycle brewers’ spent grain (BSG) have been investigated. However, little information is available on its use for composting. Considering the main parameters required for optimal development of composting, the objective of the present review was to analyze the literature to determine whether the microbial and physicochemical characteristics of BSG make it suitable for direct composting. As the main factors in the composting process, we considered the BSG moisture content, total carbon, total nitrogen, C/N ratio, and pH. As described in the literature, the BSG moisture content, C/N ratio, and pH range from 70.6% to 81.3%, 7.1 to 26.5, and 3.8 to 6.9, respectively. This C/N ratio range is lower than the composting target range (20–30). Instead, the mean moisture content in the literature is higher than the 60% to 65% recommended for composting. Optimum pH for aerobic stabilization of compost ranges from 5.5 to 7.5, while the BSG pH in the literature is typically more acidic. Therefore, BSG is not suitable for direct composting. Addition of lignocellulosic bulking agents improves the reduction of moisture content during composting, while also optimizing the substrate properties, such as C/N ratio, air spaces, and pH, to positively affect the composting process. Moreover, livestock manure should be included as a starting material to promote the composting process. In this context, two hypothetical initial mixtures of BSG plus a lignocellulosic bulking agent and livestock manure are presented.

https://www.mdpi.com/2077-0472/11/1/2/pdf

Suitability of Composting Process for the Disposal and Valorization of Brewer’s Spent Grain

The endogenous gut microbiota affects the host in many ways. Prebiotics should favour beneficial intestinal microbes and thus improve host health. In this study, we investigated how a novel class of potential prebiotic long-chain arabinoxylans (LC-AX) and the well-established prebiotic inulin (IN) modulate the gut microbiota of humanized rats. Six weeks after axenic rats were inoculated with a human faecal microbiota, their colonic microbiota was similar to this inoculum (∼ 70%), whereas their caecal microbiota was enriched with Verrucomicrobia and Firmicutes concomitant with lower abundance of Bacteroidetes. Moreover, different Bifidobacterium species colonized the lumen (B. adolescentis) and mucus (B. longum and B. bifidum). Both LC-AX and IN increased SCFA levels and induced a shift from acetate towards health-promoting propionate and butyrate respectively. By applying a high-resolution phylogenetic micro-array (HITChip) at the site of fermentation (caecum), IN and LC-AX were shown to stimulate bacterial groups with known butyrate-producers (Roseburia intestinalis, Eubacterium rectale, Anaerostipes caccae) and bifidobacteria (B. longum) respectively. Prebiotic administration also resulted in lower caecal abundances of the mucin-degrading Akkermansia muciniphila and potentially more mucin production by the host. Both factors might explain the increased caecal mucin levels for LC-AX (threefold) and IN (sixfold). These mucins were degraded along the colon, resulting in high faecal abundances of Akkermansia muciniphila for LC-AX and especially IN-treated rats. Finally, the microbial changes caused an adaptation period for the host with less weight gain, after which the host fine-tuned the interaction with this altered microbiota. Our results demonstrate that next to IN, LC-AX are promising prebiotic compounds by stimulating production of health-promoting metabolites by specific microbes in the proximal regions. Further, prebiotic supplementation shifted mucin degradation to distal regions, where mucin-degraders may produce beneficial metabolites (e.g. propionate by Akkermansia muciniphila), so that prebiotics may potentially improve gut health along the entire length of the intestine.

Arabinoxylans and inulin differentially modulate the mucosal and luminal gut microbiota and mucin-degradation in humanized rats

The increasing interest from the feed as a source of energy towards specific nutrient-yielding compounds in feeds is amongst the latest developments from scientific and industrial communities. Apart from brewers' spent grain (BSG) being relatively inexpensive feed source, nutritious with high crude protein and minerals, recent studies have explored its potential as a source of prebiotics. Prebiotics are certain feeds that are comprised of non-digestive polysaccharides that can be fed to animals and modulate the balance and activities of microbial populations in the gut. The BSG contains arabinoxylans and β-glucans whereby when consumed by animals, they promote the activity of beneficial bacteria particularly species from three genera of Bifidobacterium, Enterococcus, and Lactobacillus. The increased degradation of fibrous feed accelerates the production of short-chain fatty acids (SCFA) which serve as the primary energy sources for the anaerobic microbes. This elevated concentration of SCFA stimulates numerous physio-biological functions which include intestinal nutrients absorption, glucose balance, improvement of immunity, lipid metabolism, and suppression of pathogens such as Salmonella and Escherichia coli. To capitalize on the prebiotic potential of BSG, certain considerations need to be well taken care of and these include possible microbial dysfunctions such as rumen acidosis, different responses rates of animals due to variations in health status, age, and species as well as feed safety issues especially mycotoxin contamination which can jeopardize its inherited prebiotic benefits.

Emanuel Joel Lao

Papers

The prebiotic potential of brewers' spent grain on livestock's health: a review.