Whole wheat and barley contain the soluble fiber known as beta-glucan. Epidemiological data and clinical evidence support the health claim that various soluble fibers may lower LDL cholesterol and thus decrease the risk of cardiovascular disease.
Beta-glucans are naturally occurring polysaccharides from different sources, such as grains and microbes (Ryan et al., 2007). These unique carbohydrates often present unlike structures and contribute to dissimilar functions, which lead to disparate potential health benefits. Beta-glucan from oat, barley, and seaweed are primarily linear short β-(1,3) segments with long β-(1,4) branches. The forms from grains appear to function through a variety of mechanisms, such as reducing cholesterol reabsorption in the enterohepatic recirculation process, delaying absorption of dietary fat, and possibly enhancing intestinal fermentation by the microflora (Ames and Rhymer, 2008). Yet, β-glucan from seaweed presents a different bioactivity, which is similar to that found in microbial cell walls (Vetvicka and Yvin, 2004).
Other natural sources of beta-glucans are derived from the cell walls of microbes, such as yeasts and some mushrooms. These glucose polymers have a basic β-(1,3) structure with β-(1,6) branches. These polysaccharides affect the innate immune system by activating the complement system and enhancing macrophage and natural killer (NK) cell function (Schepetkin and Quinn, 2006; AkramienC) et al., 2007; Wichers, 2009).
The immunomodulatory modulating properties of some β-(1,3), (1,6) glucans impact the innate immune system primarily through receptors expressed on macrophages. Macrophage activity is critical in many aspects of our defense system, which wards off infection and attenuates allergic responses. For example, macrophages destroy pathogens that cross protective barriers. Orally administered beta-glucans from mushrooms appear to mitigate some allergen-specific responses and IgE titers in humans following exposure to cedar pollen (Yamada et al., 2007), house dust mites (Liu et al., 2003), and possibly even peanut-induced anaphylaxis in a murine model (Li et al., 2001).
Runners, particularly endurance athletes, frequently present exercise-induced upper respiratory infections (URI ) post events (Nieman et al., 1995). Emerging evidence from clinical studies suggests the consumption of β-(1,3), (1,6) glucan from Saccharomyces cerevisiaeB yeast can reduce the number of symptoms marathoners report, whereas the beta-glucans from oats did not affect the incidence of URI among cyclists (Talbott and Talbott, in press; Nieman et al., 2008). Using a mouse model, investigators demonstrated oatderived β-glucan may reduce morbidity and symptom severity when challenged with herpes simplex virus-1 (Murphy et al., 2008). These apparent benefits seemed to be mediated, in part, by repletion and enhanced functionality of lung macrophages.
For several decades, β-glucans from edible and non-edible mushrooms have served as an immunologic adjuvant for some cancers. The therapeutic properties may be attributed to stimulated blood cell production following radiation therapy and improved bone marrow activity, the suppression of which occurs with some chemotherapeutic drugs. Another aspect to consider is complement receptors on NK cells, neutrophils, and lymphocytes. Activation of these receptors via some β-glucans may contribute to tumor cytotoxicity (Chen and Sevior, 2007). Numerous investigations suggest that these cell wall polysaccharides protect DNA from oxidative damage initiated by lipid peroxides (Mantovani et al., 2008) and enhance the production of tumor necrosis factor alpha by macrophages (Kogan et al., 2008).
As immunomodulatory food ingredients, β-glucans are either soluble gel-forming components or insoluble particulates. These properties vary with the source and modification or degree of branching (Novak and Vetvicka, 2008). Regardless, it appears that the biological function of most of these immunomodulatory polysaccharides and their related fungal immunomodulatory proteins is preserved under typical food processing environments (Chang et al., 2007; Tong et al., 2008).
The future of β-glucans may be as medically and nutritionally appropriate ingredients in more-healthful foods. The physical properties, the physiological responses, the apparently low toxicities, and the food processing stability are desirable characteristics.
References for the studies cited above are available from the authors.
Roger Clemens, Dr.P.H.,
Scientific Advisor, ETHorn, La Mirada, Calif.
Peter Pressman, M.D.,
LCDR, Medical Corps, U.S. Navy