beta glucan (β-glucan), which is a dietary fiber readily found in oat and barley bran
Among cereals, the highest content (g per 100 g dry weight) of β-glucan has been reported for barley: 2–20 g (65% is water-soluble fraction) and for oats: 3–8 g (82% is water-soluble fraction). Other cereals also contain β-glucan but in much lower amounts: sorghum 1.1–6.2 g, rye 1.3–2.7 g, maize 0.8–1.7 g, triticale 0.3–1.2 g, wheat 0.5–1.0 g, durum wheat 0.5-0.6 g, and rice 0.13 g
Other sources of β-glucan include some types of seaweed [17] and various species of mushrooms such as Reishi, Shiitake, and Maitake [18].
Distinction between soluble and insoluble dietary fibers is based on the solubility characteristics of dietary fiber in hot aqueous buffer solutions
Insoluble fibers primarily consist of cellulose and some hemicelluloses, resistant starch, and chitin while soluble fibers include pectins, β-glucans, galactomannan gums, mucilages, and some hemicelluloses
insoluble fibers increase fecal bulk and the excretion of bile acids and decrease intestinal transit time
Soluble fibers increase total transit time by delaying gastric emptying and also slow glucose absorption
only soluble viscous fibers delay gastric emptying time and slow glucose absorption while nonviscous soluble fibers primarily act as a substrate for microbial fermentation in the colon