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.