The Sources of β-Glucans
Bakers’ yeast as well brewers’ yeast has a long history of safe consumption. It has been used for over a thousand of years in the production of bread, wine, and beer. Although allergies to Sacharomyces cerevisiae from food consumption might occur, they are rare. In general, yeast products are very well tolerated. Yeast is rich source of beta-glucans.
Beta-glucan are derived from two main vegetable sources:
- Water soluble and small molecule β-glucans – mostly cereal derived: oat, rye, barley, etc.
- Insoluble and macro molecule β-glucans – mostly mushroom derived (yeast, shiitake, schizophyllum, reishi, etc.)
The first group has short glycosidic chains bonds at β 1→3 and 1→4 position and it is water soluble. This group of beta-glucans reveals strong metabolic activty reducing elevated suger and lipid blood level (cholesterol).
The second group has long glycosidic chains combined bonds at β 1→3 position and short lateral chains at 1→6 position. It is water insoluble. This group reveals immune system effective stimulating properties.
Yeast is single-celled microorganisms classified as members of the fungus kingdom. Yeast is used by mankind for thousands of years. There are two main types of yeast: baker's yeast and brewer's yeast (wine and beer may slightly differ). The main property of yeast is that it consumes sugar (carbohydrates) and produce gas (carbon dioxide) or/and alcohol (ethanol) in a process called fermentation. Consumption of raw yeast may cause some side effects. Yeast processing significantly reduces and cooking or extraction eliminates any such risk.
Uptake of 1,3/1,6-β-Glucans
Uptake of large-molecule, insolouble β-glucan has been shown in mice with soluble and particulate yeast (1,3)-(1,6)-glucans labeled with fluorescein. Both types of yeast β-1,3-glucans were taken up by gastrointestinal macrophages via so called M-cells. Peyer's Patches are covered by a tissue that contains specialized cells called microfold cells (M cells). M cells have the unique ability to transport organisms and particles from the intestine to immune cells located in a pocket-like structure underneath. Those immune cells are macrophages, lymphocytes (T cells and M cells) and dendritic cells, which receives the antigens and delivers them to the other immune cells. These cells then moves to the lymph nodes where the immune response is amplified. The activated cells were also transported to the spleen and bone marrow. Also, in vitro experiments have shown that β-glucans were degraded inside macrophages and released into the culture medium, which makes them eventually available for the circulating system and a systemic distribution.
Orally administered β-glucans induced phagocytic activity, oxidative bursts, and IL-1 production of peritoneal macrophages in mice. A higher phagocytic activity and oxidative metabolism of neutrophils and monocytes, indicating an immune restoring activity of yeast β-glucan has also been shown in rats. However, not only the cellular but also the humoral acute phase immune reaction is affected by yeast β-glucan feeding as shown by increased lysozyme and ceruloplasmin activitiy.