Analysis of mixed linkage beta-glucan content and structure in different wheat flour milling fractions

b-glucan is a dietary fibre component with health benefits that relate to its structure and solubility. The polysaccharide structure consists predominantly of beta-(1-4) linked cellotriosyl (G3) and cellotetraosyl (G4) units joined together with beta-(1,3) linkages. The ratio of G3:G4 blocks affects the solubility with very high or very low ratios causing lower solubility. Wheat, a major staple crop, is a source of beta-glucan in the human diet; however, there is a lack of research on beta-glucan in wheat, especially white flour which is used in many food products. Here we quantified beta-glucan in different wheat milling fractions, showing a low content in the first and second break (white) flour fractions (0.2%) with increasing amounts in bran flour (0.5%), wholemeal (0.8%) and bran (2.8%). A high proportion (30%) of beta-glucan in the white flour fractions was soluble, while in bran a far smaller proportion (10%) was soluble. In agreement with differences in solubility, the G3:G4 ratio also differed, with the white flour fractions having lower ratios (similar to 2.5) and bran-containing fractions having higher ratios (similar to 3.8). We conclude that while total beta-glucan in white flour is low, it is substantially soluble, and that high extraction and wholemeal flours have the potential to be a significant source of beta-glucan.