Effects of barley and oat β-glucan structures on their rheological and thermal characteristics

In order to understand the relationship between chemical structure and physical properties of cereal β-glucans, the β-glucans with identical Mw (98.4–99.2 kDa) and Rg (21.1–22.0 nm) were isolated from chal and gwangan barley, and ohl oat, and their linkage structure, flow behavior, and thermal properties were investigated. Previously, we established a purification method of 3-O-cellobiosyl-glucose (DP3) and 3-O-cellotriosyl-glucose (DP4) (Yoo, Lee, Chang, Lee, & Yoo, 2007) and applied these authentic standards to quantify the ratio of β-(1,4)/(1,3) linkages in cereal β-glucans. β-Glucans isolated from two barley cultivars had greater proportion of DP3 than did the oat, and within barley cultivars chal barley β-glucan had significantly larger amount of DP3 over gwangan cultivar. Thus, chal barley β-glucan had the greatest molar ratio (2.53) of DP3 to DP4, and ohl oat had the lowest (1.51). While all the β-glucan solutions showed strong shear thinning behavior, ohl oat β-glucan with higher proportion of DP4 exhibited the highest viscosity among the β-glucan samples. After 3 freeze-thaw cycles of 3% (w/v) β-glucan samples, chal barley β-glucan had lower onset (To) and peak (Tp) temperatures (28.3 and 36.7 °C, respectively) than those of gwangan barley (33.6 and 39.9 °C) and ohl oat (37.9 and 46.9 °C) did, and the heat scan profiles were thermoreversible. The To and Tp of inter-chain associations decreased as the DP3:DP4 ratio of the β-glucan increased. From this study, it was suggested that cellotetraosyl units and longer β-(1,4)-linked segments would be a major contributor for improving solution viscosity and gel formation of cereal β-glucans.