β-glucan


What is β-glucan?

β-glucan (or beta-glucan) is a major component of water soluble cereal fibre and an important part of oat dietary fibre. β-glucans are non-starch polysaccharides composed of glucose molecules in long linear glucose polymers with mixed β-(1→4) and β-(1→3) links with an approximate distribution of 70% to 30%.

beta-glucan structure.jpg

 

The β-(1→3) linkages break up the uniform structure of the β-glucan molecule and make it soluble and flexible (see Figure above). 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 four or more consecutive β-(1→4) linked glucose units. The molar ratio of cellotriose to cellotetraose units (DP3:DP4) is typically 1.5 - 2.3 as far as oat β-glucan is considered.

 

The molecular weight of β-glucan varies between 50 and 3000 kDa. 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. 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 wt% (weight percent). With lower molecular weight preparations (MW ≤ 200,000) of oat, it was possible to add up to 2.0 wt% β-glucan to the soup.

 

About β-glucans effects on health, see section Oats and Health.

Where is β-glucan located in oat grain?

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).


oat beta-glucan_location in grain.jpg

Figure. Cross sections of oat bran layer stained with Calcofluor and Acid Fuchsin. Endosperm cell walls rich in beta-glucan appear as blue and protein as brownish red. Courtesy of VTT Technical Research Centre of Finland.



Beta-glucan usually comprises 2-8 % (dry weight) of the oat whole grain. Several factors affect the concentration of beta-glucan including cultivar variation and the growing conditions (e.g. nitrogen level, temperature and rainfall). The content of dietary fibre and beta-glucan varies between different oat products. Typical concentrations (% of dry weight) are presented in the Table below.

 

  Oat endosperm flour
Whole grain products  Conventional oat bran products
Oat bran
concentrates 
Beta-glucan
isolates 
 
Dietary fibre (%)

5 - 10

11 - 17

15 - 32

42 - 47

47
 
Beta-glucan (%)

1 - 2

2 - 8

8 - 12

15 - 249

Up to 36

 

 

 

 

 

 

 

Lindberg Hartvigsen, 2013

U.S. Department of Agriculture, Agricultural Research Service, 2011

Hüttner et al., 2010

Wood, 2010

Zhang et al., 2009

Shewry et al., 2008

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

Yao et al., 2007

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.

Tapola et al., 2005

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

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.

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

Kerckhoffs et al., 2003

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.

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.

Pick et al., 1996

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.

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.

Miller et al., 1993

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.

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.

AACC Committee, 1989

Henry, 1987