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The β‐glucans are composed of D‐glucopyranose units with β‐1→4 and 1→3 linkages types. The number of adjacent glucose units with the same linkage determines the complexity of β‐glucans with its various molecular weights, solubilities, viscosities and three‐dimensional configurations. For the water‐soluble β‐glucans such as the (1,3/1,4) β‐glucan that is rich in oats and barley, the (1,4)‐β‐linkages are present mainly in groups of two or three adjacent linkages (Figure 4.5). The ratio of randomly arranged cellotriosyl (DP3) and cellotetraosyl residues (DP4) is used to represent the structural property of (1,3/1,4) β‐glucan, and β‐glucans with a ratio of 1.5‐2.5 tends to form a gel‐like matrix, while lower and higher ratios tend to form aggregates (Burton et al. 2010). The ratio of DP3/DP4 from oats is in the range of 1.5–2.3, while a ratio of 1.8–3.5 was found for barley‐sourced β‐glucan, while the ratio is even higher in wheat (3.0–4.5) (Lazaridou and Biliaderis 2007). There are also long cellulosic oligomers (DP>4), such as in barley. The structural diversity of β‐glucans determines differences in physiochemical properties and related health benefits.

Figure 4.5 The general structure of cereal mixed linkage (1→3) (1→4)‐β‐D‐glucan

(Source: Lazaridou and Biliaderis 2007)