This article presents an overview of the recent advances into the health promoting potentials of oat β-glucan. Oat β-glucan (OβG) consists mainly of the linear polysaccharide (1 3), (1 4)-β-D-glucan and is often called β-glucan. This soluble oat fiber is able to attenuate blood postprandial glycemic and insulinemic responses, to lower blood total cholesterol and low-density lipoprotein (LDL) cholesterol, and to improve high-density lipoprotein (HDL) cholesterol and blood lipid profiles as well as to maintain body weight. Thus, OβG intake is beneficial in the prevention, treatment, and control of diabetes and cardiovascular diseases. In addition, OβG can stimulate immune functions by activating monocytes/macrophages and increasing the amounts of immunoglobulin, NK cells, killer T-cells, and so on, which will improve resistance to cancer and infectious and parasitic diseases, as well as increase biological therapies and their prevention. All these health benefits of OβG may be explained by its physicochemical properties (such as viscosity, molecular weight) which can be affected by extraction methods and its behavior in gastrointestinal tract. Articles documenting these health benefits and effects are reviewed.
The common oat (Avena sativa) is species of cereal grain mainly grown for its utilization for human consumption as oatmeal as well as for livestock feed. Oat has always been regarded as a health-promoting food without clear knowledge of its specific health-related effects. However, today it is known for its effects on satiety and retarded absorption of nutrients as well as a deterrent of various disorders of the gastrointestinal tract. These beneficial effects are chiefly due to the soluble fiber content of oats. Today oats is among the richest and most economical sources of soluble dietary fiber The present interest in soluble oat fiber originated from reports that showed that dietary oats can help in lowering cholesterol (Braaten and others 1994; Hsing-Hsien and Ming-Hoang 2000; Bae and others 2010; Drozdowski and others 2010; Tiwari and Cummins 2011), postprandial blood glucose level (Wood and others 2000; Hooda and others 2010; Regand and other 2011; Dong and others 2011; Tiwari and Cummins 2011) as well as modifying immune response and reducing risk of colon cancer。
Whereas oat is an inexpensive source, and extraction of beta-glucan is very difficult, oat beta-glucan becomes the more inexpensive beta-glucan.
Ever since the 1st report on the health-promoting potentials of oat beta-glucan, several studies have been carried on the subject matter on various health problems. Moreover, consumption and utilization of the material have increased greatly among consumers, especially in the developed societies where issues of chronic diseases continue to be of major health concern. In order to provide current information on the subject matter, this article is an attempt to review recent advances into the general health benefits of oat beta-glucan.
Gastrointestinal effects of oat β-glucan
Both soluble and insoluble oat fibers have gastrointestinal effects: soluble fiber mainly due to its high swelling and water-binding ability, and as a substrate in colon fermentations and insoluble fiber due to its bulking effect.
The gastrointestinal effects of oat β-glucan were well reviewed by Mälkki and Virtanen (2001). However, in this article we intend to emphasize some solution behavior of oat β-glucan under gastrointestinal conditions. In the stomach, oat β-glucan has a smaller hydrodynamic size; its aggregates seem to be reduced or disrupted. Low pH could be responsible for that because no change was observed when pepsin was absent in the stomach (Ulmius and others 2012).
Ulmius and others (2011) reported in their study that the release of oat-β-glucan was mainly due to gastric digestion. They further observed that the process of milling to smaller particles could improve the releasability of β-glucan from 20% to 55%. Moreover, it reduced protein and starch matrices to 5% and fat to 45%. Wang and others (2002) have reported that the rate of recovery of β-glucan increased to 90% after microwave heating compared to 75% for samples treated by conventional dissolution. This was due to the large particle size of β-glucan aggregates in the sample which was reduced or disrupted after microwave heating leading to increased recovery of β-glucan.
Dikeman and others (2006), in their study to quantify the viscosity of soluble and insoluble fibers at various concentrations in solution, determined the effects of altering shear rate on the viscosity of these solutions as well as the effects of fibers source, incubation time, and shear rate on the viscosity of solution in a two-stagein vitro digestion simulation model. The authors reported that a short exposure time (1–2 h) of oat bran to gastric fluids in vitro, and in pigs, increased the viscosity. Increase of viscosity was due to the hydration of the substrate. However, a longer exposure decreased the viscosity, which could have been caused by gastric conditions and resulted in a breakdown of the polymeric structure.
Oat dietary fiber when ingested, starts to imbibe water, swell, and dissolve in relationship to its size and previous hydrothermal treatments, the increased volume causes a distension of the stomach, thus affecting satiety. Data on the effect of oat fiber on stomach emptying are controversial. A concept often referred to is that viscous dietary fibers reduce the rate of gastric emptying and that coarse particles leave the stomach sooner (Mälkki and others 2001).
Health benefits of oat beta-glucan
Oat bran, the edible outermost layer of the oat kernel is rich in soluble fiber and is called beta-glucan. It is a natural polymer comprised of individual glucose molecules that are linked together by a series of beta-(1, 3) and beta-(1, 4) linkages, comprising a class of nondigestible polysaccharides called beta-D-glucans. This unique array of linking promotes several consumer health benefits.