What is β-glucan?

Oat β-glucan a mixed-linkage polysaccharide of D-glucose units, and an important part of oat dietary fibre. β-Glucan is a major component of the water extractable fibre fraction (Manthey et al. 1999). The bonds between D-glucopyranosyl units in β-glucan are either β-1,3 or β-1,4 linkages. The 1,3-linkages break up the uniform structure of the β-D-glucan molecule and make it soluble and flexible (see Figure below). Structural analysis shows that β-glucan is composed primarily of β-1,3 linked cellotriosyl and cellotetraosyl units, but there are also regions that are more cellulose-like in character, with 4 or more consecutive β-1,4 linked glucose units (Wood et al. 1993). The molar ratio of cellotriose to cellotetraose units (DP3:DP4) is typically 1.5 - 2.3 as far as oat β-glucan is considered (Miller and Fulcher 1995).










The soluble β-glucans make viscous, shear thinning solutions even at low concentrations. The viscosity is related to the molecular weight and is strongly dependent on the concentration (Åman et al. 2004, Anttila et al. 2004). Lyly et al. (2004) observed that with an oat β-glucan preparation of high-molecular weight (average MW = ca. 2,000,000), the maximum practicable concentration of β-glucan in a soup was 0.5 w-%. With lower molecular weight preparations (MW ≤ 200,000) of oat, it was possible to add up to 2.0 w-% β-glucan to the soup.

Where is β-glucan located in oat grain?

β-glucan usually comprises 3,6 - 5,1 % (dw) of the oat whole grain (Hampshire 2004). The several factors that affect the concentration of β-glucan include cultivar variation and the growing conditions (e.g., nitrogen level, temperature and rainfall) (Asp et al. 1992, Brunner and Freed 1994). β-glucans are located throughout the starchy endosperm. They are concentrated in the bran, more precisely in the aleurone and sub-aleurone layer (see Picture below).

The content of dietary fibre and β-glucan varies between different oat products. Typical concentrations
(% of dry weight) are presented in the Table below.

References

Åman, P., Rimsten, L., Andersson, R. (2004) Molecular weight distribution of β-glucan in oat-based foods. Cereal Chem 81, pp. 356-360.

Anttila, H., Sontag-Strohm, T., Salovaara, H. (2004) Viscosity of beta-glucan in oat products. Agric Food Sci 13, pp. 80-87.

Asp, N.-G., Mattsson, B., Onning, G. (1992) Variation in dietary fibre, β-glucan, starch, protein, fat and hull content of oats grown in Sweden 1987-1989. Eur J Clinical Nutr 46, pp. 31-37.

Brennan, C.S., Cleary, L.J. (2005) Review: The potential use of cereal (1→3,1→4)-β-D-glucans as functional food ingredients. J Cereal Sci 42, pp. 1-13.

Brunner, B.R., Freed, R.D. (1994) Oat grain β-glucan content as affected by nitrogen level, location, and year. Crop Sci 34, pp. 473-476.

Cervantes-Martinez, C.T., Frey, K.J., White, P.J., Wesenberg, D.M., Holland, J.B. (2002) Correlated responses to selection for greater β-glucan content in two oat populations. Crop Sci 42, pp. 730-738.

Hampshire, J. (2004) Variation in the content of nutrients in oats and its relevance for the production of cereal products. In: Proceedings of the 7th International Oat Conference. Helsinki, Finland. Peltonen-Sainio, P., Topi-Hulmi, M. (eds.) Jokioinen: MTT Agrifood Research Finland, Agrifood Research Reports 51, p. 126.

Lyly, M., Salmenkallio-Marttila, M., Suortti, T., Autio, K., Poutanen, K., Lähteenmäki, L. (2004) The sensory characteristics and rheological properties of soups containing oat and barley beta-glucan before and after freezing. Lebensm-Wiss Technol 37, pp. 749-761.

Manthey, F.A., Hareland, G.A., Huseby, D.J. (1999) Soluble and insoluble dietary fiber content and composition in oat. Cereal Chem 76, pp. 417-420.

Miller, S.S., Fulcher, R.G. (1995) Oat endosperm cell walls: II. Hot-water solubilization and enzymatic digestion of the wall. Cereal Chem 72, pp. 428-432.

Wood, P.J. (1993) Physicochemical characteristics and physiological properties of oat (1→3),(1→4)-β-D-glucan. In: Wood, P.J. (ed.) Oat Bran. St. Paul, MN, USA: Amer Assoc Cereal Chem, pp. 83-112.

Wood, P.J. (2007) Cereal β-glucans in diet and health. J Cereal Sci 46, pp. 230-238.