Barley grain β-glucans: unravelling the biochemistry and molecular biology of mixed linkage β-glucans for health and malting industry

Abstract β-Glucans are polysaccharides found in bacterial exo-polysaccharides, fungi (Basidiomycota), and cereal grains. In fungi and bacteria, β-glucans primarily consist of β-(1,3)- and β-(1,6)-linked glucose units, while in cereal grains, such as barley and oats, they are predominantly mixed-linkage β-(1,3;1,4)-glucans. This mixed-linkage structure is a defining characteristic of cereal β-glucans. Barley grain β-glucans are especially intriguing for their numerous health advantages, making barley a promising candidate for health food applications. The genes, such as HvTLP, HvGAMYB, and HvCslF, are relevant for malting and brewing. They have been linked to reduced cholesterol and postprandial blood glucose levels showed to be a functional food. Understanding structural features like the degree of polymerisation (DP3 to DP4 ratio) and molecular weight is crucial for comprehending their solubility, gelation tendencies, and physiological effects. High β-glucan content is favoured for healthy food applications, while lower content is desirable for malt barley to ensure efficient malting and brewing. The current review provides valuable insights into barley grain β-glucans, paving the way for future research to enhance their utilisation in functional foods, nutraceuticals, and brewing applications.