Biological Activity and Developmental Utilization of Yeast β-Glucan

In recent years, yeast β-glucan has attracted increasing attention due to its diverse biological activities. β-glucan is mainly composed of β-(1→3), β-(1→4), and β-(1→6) glucosidic linkages, and is widely found in many bacteria, fungi, and higher plants. Medical studies have demonstrated that β-glucan possesses a variety of immunomodulatory functions, such as antitumor, antiviral, antioxidant, anti-radiation, blood glucose–lowering, and cholesterol-reducing activities. Among these, the research on β-glucan derived from yeast is the most extensive and in-depth. β-glucan is one of the main components of the yeast cell wall, accounting for 30%–60% of the cell wall’s dry weight.

Because yeast β-glucan possesses high biological activity, low caloric value, and strong water-holding capacity, it can be widely used as a functional ingredient, fat substitute, and dietary fiber in the fields of pharmaceutical development, animal feed, and health food production. It is a functional food additive worthy of further research and development.

1. Extraction of Yeast β-Glucan

β-glucan is composed of β-(1→3)-glucan and β-(1→6)-glucan in a ratio of 85:15. Previous methods for extracting yeast β-glucan mainly included acid treatment, alkaline treatment, acid–alkali combined methods, and enzyme–alkali extraction. These extraction methods are characterized by being fast and efficient, but they require large amounts of acid and alkali, involve complex processes, and have high labor intensity. In addition, acid and alkali reagents tend to corrode equipment and pollute the environment, and during extraction, partial degradation of β-glucan often occurs, resulting in lower yield and reduced biological activity.

At present, extraction technology has been significantly improved. Using modern enzymatic engineering techniques, β-glucan can be obtained through a three-step process consisting of autolysis, enzymatic hydrolysis, and alkali extraction. This process produces β-glucan with high purity, avoids the limitations of traditional methods, and simultaneously improves the yield and purity of the product. The resulting β-glucan has an intact molecular chain and a high molecular weight.

2. Biological Activity of Yeast β-Glucan

The unique structure of yeast β-glucan gives it various physiological activities, such as reducing cholesterol and blood lipid levels and enhancing the body's immune function. Numerous studies have demonstrated that the immunoregulatory mechanism of yeast β-glucan lies in its ability to bind specifically to immune cells of both animals and humans, including monocytes, macrophages, neutrophils, and natural killer (NK) cells. Through this specific binding, yeast β-glucan stimulates lymphocytes and activates macrophages within the body, thereby enhancing the organism’s immune activity. Therefore, yeast β-glucan possesses multiple immunomodulatory functions.

2.1 Antitumor and Anticancer Effects

The primary goal of current antitumor research is to enhance the activity of macrophages in human tissues, and β-glucan possesses this function. Cheung N.K. and others used immunodeficient xenograft tumor models to study β-(1→3)-glucan and examined the relationship between its antitumor efficacy and its physicochemical properties. The study found that oral administration of β-glucan greatly enhanced the antitumor effect established by monoclonal antibodies (mAb) in mice.

2.2 Antioxidant and Anti-radiation Effects

β-glucan can effectively remove free radicals from the body, protecting macrophages from free radical damage during and after radiation exposure, thereby allowing these cells to continue functioning normally. Cell culture experiments have shown that methylated β-glucan can inhibit the depletion of antioxidant molecules under ultraviolet (UV) irradiation, promote keratin growth, and thus protect skin cells. Research by Patchen M.L. and others demonstrated that water-soluble β-glucan can accelerate recovery after cobalt-60–induced radiation exposure in mice. Treatment with β-glucan enhanced the recovery ability of irradiated mice, increased bone marrow activity, elevated the number of white blood cells, and simultaneously boosted spleen cell counts.

2.3 Promoting Wound Healing

Since macrophage activity plays an important role in surgery and wound healing, β-glucan is capable of participating in the body's natural defense mechanisms and accelerating skin wound repair. Waisun et al. found that applying 20–100 mg/ml yeast β-glucan to the injured limb of animals significantly accelerated wound healing. When 0.1–0.2 mg/kg body weight of soluble β-glucan was administered, it was found to reduce postoperative infection rates in thoracoabdominal surgery.

2.4 Reduction of Cholesterol and Blood Lipids

The distinctive structural characteristics of β-glucan facilitate the metabolism of lipoproteins and the release of fatty acids, promoting the breakdown of large lipid molecules in the bloodstream into smaller ones. Consequently, β-glucan exerts a clarifying effect on serum turbidity caused by excessive lipids, leading to a significant reduction in blood cholesterol levels. Nicolosi et al. conducted a study involving 15 obese male subjects with hypercholesterolemia. Throughout the study, participants maintained stable body weight. By the seventh week, total cholesterol concentration in the blood had decreased by 8%, and an additional 6% reduction was observed by the eighth week relative to the seventh. These findings indicate that yeast-derived β-glucan has a notable hypocholesterolemic effect, effectively lowering serum cholesterol levels.

3. Development and Utilization of Yeast β-Glucan

3.1 Development and Application in Medicine

Yeast β-glucan overcomes the limitations of traditional antibiotics, probiotics, and enzyme preparations. It is characterized by low dosage requirements, natural origin, absence of residues, and strong stability. Moreover, it enhances the immune function of animals and promotes growth. Moon and Won Kook et al. reported that biologically synthesized soluble β-glucan exhibits strong antiviral activity against avian influenza and may be used for the treatment or prevention of this disease. β-glucan can induce macrophages to produce interleukin-2 (IL-2) and nitric oxide (NO), thereby enhancing immune responses. It also shows strong inhibitory effects on the proliferation of tumor cells. Clinically, β-glucan is often applied to prevent and treat immune deficiencies, cancer, and related disorders. Research conducted by Kong Weihua and colleagues demonstrated that β-glucan has significant protective and therapeutic effects on various gastric ulcer models, including water-immersion stress-induced gastric ulcers in mice, ethanol- or aspirin-induced gastric injury, and acetic acid-induced chronic gastric ulcers in rats. These findings indicate that β-glucan exerts remarkable gastroprotective and healing-promoting properties.

3.2 Application in Animal Feed

Yeast β-glucan is an excellent natural immunopotentiator that enhances both nonspecific and specific immune responses in organisms. It can be used in conjunction with immunostimulants to improve vaccine efficacy and represents an important approach to enhancing animal health. β-glucan has been widely applied in animal feed formulations.

Since fish are the most primitive vertebrates and young or juvenile animals possess underdeveloped immune systems, their resistance to infection relies primarily on nonspecific immune responses. Therefore, the use of yeast β-glucan plays a vital role in improving immunity and disease resistance in such animals.

Selvaraj et al. demonstrated that intraperitoneal injection of soluble yeast β-glucan in carp significantly enhanced both the specific and nonspecific immune responses of the fish. Similarly, Coufie and colleagues used β-glucan as an antibiotic substitute by incorporating it into the daily feed of piglets, broiler chickens, and other livestock, and found that it markedly improved both humoral and cellular immune functions in these animals.

3.3 Application in Health Foods

Because β-glucan possesses high viscosity, strong water retention, and excellent emulsifying stability, it is widely used in the food industry as a thickener, humectant, binder, and emulsifying stabilizer in seasonings, desserts, and other food products. Since β-glucan is resistant to digestion in the human gastrointestinal tract, it can serve as a non-caloric food additive that provides a fat-like texture. According to research by Wang Sen and others, the use of β-glucan as a fat substitute in meat products not only enhances the smoothness and richness of low-fat meats but also improves their texture, hardness, cohesiveness, chewiness, and overall acceptability. Furthermore, β-glucan is non-caloric and rich in dietary fiber, which helps inhibit lipid absorption, promote bile acid excretion, and enhance intestinal motility. Therefore, β-glucan can function both as a dietary fiber supplement and as a high-quality health food additive in the food industry.

With the continuous improvement of living standards, consumers are paying increasing attention to their health, leading to a growing demand for health products. Yeast β-glucan possesses multiple physiological functions, including enhancing immune activity, exhibiting antitumor effects, and reducing cholesterol and blood lipid levels, with remarkable efficacy. At present, both domestic and international health food industries mainly incorporate β-glucan as a key ingredient aimed at boosting human immunity and lowering blood lipids, and its development trend remains strong.

4. Conclusion

Research on yeast β-glucan began abroad in the 1940s, with considerable progress made in extraction, detection, and structural analysis. In contrast, current studies in China remain largely at the experimental stage. Therefore, existing yeast β-glucan products are still far from meeting domestic and international market demands, indicating substantial commercial potential for further development of yeast β-glucan.

However, the existing separation and purification methods for insoluble β-glucan are limited by low purity, low yield, and severe contamination. In particular, the use of acidic reagents during extraction often causes polysaccharide degradation, thereby reducing the biological activity of β-glucan. Consequently, further research and technological improvements are needed to develop mild and clean separation and purification techniques, expand production capacity, and meet the needs of various industries.

Moreover, β-glucan, as an effective immunopotentiator, has already been widely applied in the prevention and treatment of various infectious diseases caused by pathogens in animals, achieving remarkable results. However, further in-depth and systematic studies on its immunological mechanisms are still needed to enable broader and more extensive applications in the future.

Utilizing discarded brewer’s yeast to extract yeast β-glucan can significantly enhance the economic efficiency of the brewing industry, reduce environmental pollution, and serve as an effective approach to developing a circular economy through the reuse of waste yeast resources.

In conclusion, with the deepening of research on yeast β-glucan and the improvement of production processes, as well as the comprehensive utilization of discarded brewer’s yeast, the development and application of yeast β-glucan are expected to achieve even broader and more promising progress.