β-Glucans and MOS in Pet Food: Origin, Properties, Benefits

Yeast-Based Ingredients in Pet Foods

Yeast-based ingredients derived from ethanol production have been widely used in pet foods for decades, mainly as a source of protein and other nutrients (such as B-complex vitamins) and as a palatability enhancer. However, yeast has typical components in its structure that make up the cell wall: β-glucans and mannan-oligosaccharides (MOS). The concentration and availability of these carbohydrates vary according to the type of yeast (Saccharomyces cerevisiae or others) and the fermentation process (brewers, bakers, molasses, distillers' grains, etc.), as well as the following technologies applied to obtain different final products (inactive dry, autolyzed, hydrolyzed, etc.).

β-Glucans

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The β-glucans in the yeast cell wall are β-1,3 and 1,6-glucans, different from those found in cereals (such as oats, bran, and others), which are β-1,4 and 1,3-glucans. This physicochemical difference will affect their biological function because branched or linear β-1,4-glucans have limited activity (major proportion in plant cells), while β-1,3-glucans with additional branching have the greatest immunomodulatory effect (PETRAVIĆ-TOMINAC et al., 2010). Thus, the β-glucans in the cell wall of Saccharomyces cerevisiae consist mainly of β-1,3-glucans linked in a central backbone with β-1,6-glucan branches of varying sizes (PETRAVIĆ-TOMINAC et al., 2010), which in turn are linked to manno-proteins, serving as an anchor for the structure and integrity of the manno-protein layer (MAGNANI & CASTRO-GÓMEZ, 2008).

MOS

The mannan-glucan complex will maintain the primary stability of MOS as it is and its insolubility in water. This is crucial for its biological function in the animal's gut. The main known mode of action of MOS is to serve as a binding site for pathogenic bacteria, preventing their adhesion to the intestinal epithelium and subsequent colonization and infection (MORAN, 2004). Bacteria such as Salmonella and E. coli use type 1 fimbriae, a mannose-specific lectin, to recognize glycoproteins on the surface of enterocytes (MORAN, 2004). Thus, this mechanism controls and reduces the bacterial enteric load and infection.

MOS is widely referred to and classified as a prebiotic in the literature; however, it may be possibly misunderstood, as the definition of a prebiotic is 'a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon and thus improves host health' (definition by Glenn & Roberfroid, 1995). Subsequently, the concept was updated by the International Scientific Association of Probiotics and Prebiotics (ISAPP) as: 'a selectively fermented ingredient that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thereby conferring health benefit(s) to the host.' According to ISAPP, the most studied and used prebiotics are inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS), and more recently, human milk oligosaccharides (HMOs).

Benefits of Pet Food

Studies on dogs in the literature have reported the benefits of MOS supplementation related to changes in the gut microbiota (significantly increasing beneficial bacteria and decreasing pathogenic bacteria), digestive system (intestinal integrity, reduced fecal odor, and improved stool quality), modulation of immune system responses (phagocytic activity, interleukins, immunoglobulins), among others (SWANSON et al., 2002; GRIESHOP et al., 2004; MIDDELBOS et al., 2007; PAWAR et al., 2017; THEODORO et al., 2019). However, many studies report the use of a yeast cell wall product (a combination of β-glucans and MOS) or do not fully clarify the composition of the MOS product used. This could lead to a misinterpretation of the mode of action and benefits of MOS vs. β-glucans.

The body does not synthesize β-glucans, so they must be recognized by the immune system, inducing immune responses (PETRAVIĆ-TOMINAC et al., 2010), known as immunomodulators. The process begins with recognition by phagocytic cells (macrophages, monocytes, dendritic cells, neutrophils, natural killers) with a toll-like receptor on their cell surface, which recognizes microbial patterns and induces an immediate innate immune response. The structure that allows recognition by the immune system is the pathogen-associated molecular patterns (PAMPs), and among the best known are β-glucans, which trigger responses to protect the host against pathogen invasion, characterizing innate immunity (MAGNANI & CASTRO-GÓMEZ, 2008). After this activation and phagocytosis, the phagocyte presents a processed antigen fragment. It stimulates a chain response by releasing pro-inflammatory cytokines and activating the production, release, and mobilization of additional phagocytic cells (produced in the bone marrow) (PETRAVIĆ-TOMINAC et al., 2010), phagocytic activity, and other cell-mediated immune responses.

This immunomodulatory effect means training the innate immune system and preparing it for a faster, better, and smarter response to challenges (PETRAVIĆ-TOMINAC et al., 2010). The practical result is reducing the inflammatory process (costing less to metabolism), controlling infections and their consequences (oxidative stress, cell damage, etc.), and improving the production of immunoglobulins and antibodies (against specific pathogens/antigens or vaccine titers).

Several purified and concentrated β-glucan products are available, and their immunomodulatory effect has been proven over the years, as well as when β-glucans are complexed with MOS in the yeast cell wall. These benefits seem essential for puppies (due to the developmental stage of the immune system and intestinal tract, as well as the intense vaccination period), elderly animals (due to the susceptibility of the immune system at advanced ages), animals with intestinal problems, or diseases that can cause a depression in immune response.

Conclusion

MOS and β-glucans are key components of yeast products. Their composition, concentration, and availability are closely related to the type of yeast they come from. MOS and β-glucans benefit pet food diets due to their interesting properties for balancing microbiota, preserving intestinal health, and modulating the immune response. Having a deeper understanding of these key properties helps to better appreciate them in pet food applications and allows for their tailored use to address specific challenges that companion animals face, such as growth, reproduction, and recovery.

Source: ICC Animal Nutrition

References

1. Grieshop, C.M, et al. Gastrointestinal and immunological responses of senior dogs to chicory and mannan-oligosaccharides. Arch Anim Nutr. 2004 Dec;58(6):483-93. doi: 0.1080/00039420400019977.
2. International Scientific Association of Probiotics and Prebiotics (ISAPP). Consulted on September 19th, 2023. https://isappscience.org/for-scientists/resources/prebiotics/
3. Magnani, M. & Castro-Gómez, R.J.H. β-glucans from Saccharomyces cerevisiae: constitution, bioactivity and obtaining. Semina: Ciências Agrárias, Londrina, v. 29, n.3, p. 631-650, jul./set. 2008.
4. Middelbos, I.S. et al. A dose-response evaluation of spray-dried yeast cell wall supplementation of diets fed to adult dogs: effects on nutrient digestibility, immune indices, and fecal microbial populations. J Anim Sci. 2007 Nov;85(11):3022-32. doi: 10.2527/jas.2007-0079.
5. Moran, C.A. Functional components of the cell wall of Saccharomyces cerevisiae: applications for yeast glucan and mannan. In book: Nutritional biotechnology in the feed and food industries, Nottingham University Press, pp.283-296, 2004.
6. Pawar, M.M. et al. Effect of dietary mannanoligosaccharide supplementation on nutrient digestibility, hindgut fermentation, immune response and antioxidant indices in dogs. J Anim Sci Technol. 2017 May 11;59:11. doi: 10.1186/s40781-017-0136-6.
   
   
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