Cell wall polysaccharides in cereals: chemical structures and functional properties
β-Glucans and arabinoxylans are the two primary cell wall structural components in cereals, such as wheat, oat, barley and rye. The relative amounts of the two polysaccharides vary with species and growing environments. The cell walls of barley and oats are generally rich in β-glucan, whereas rye and wheat cell walls contain higher levels of arabinoxylans. Cereal β-glucan is a mix linked (1 → 3) (1 → 4)-β-d-glucan composed of two major building blocks: a trisaccharide and a tetrasaccharide unit: the combination of the two units is over 90%. The ratio of the two building blocks is used as a fingerprint for each β-glucans: it is 4.5, 3.3, 2.2 for wheat, barley and oat β-glucan, respectively. Of the two types of cell wall polysaccharides in cereals, β-glucan received greater attention due to its proved beneficial physiological effect as an excellent source of soluble dietary fibre for significantly attenuating blood glucose and insulin levels and its demonstrated ability to reduce low-density lipoprotein cholesterols (LDL) in serum. The ability of cereal β-glucan to attenuating blood glucose, insulin levels is linked to the viscosity produced by cereal β-glucans in a linear relationship. It is also demonstrated that the functional properties of cereal β-glucans are determined by their structural features and molecular weight: a higher trisaccharide to tetrasaccharide ratio favours gel formation and faster gelation process, and ultimately, gives stronger gels. Cereal β-glucan also demonstrated an unusual behaviour by forming gel faster and yielding stronger gels at lower molecular weight (above minimum gelation molecular weight). Such a structure–function relationship was established based on rheological, light scattering and computer modelling studies which cover both dilute and concentrated concentration regimes: high tri/tetra ratio gives high proportion of consecutive trisaccharide unit which favours the intermolecular association of β-glucan chains; on the other hand, low molecular weight chains have higher mobility that promotes intermolecular chain–chain interactions, hence, lead to faster gelation process and formation of stronger gels. Research also revealed that processing and storage conditions, such as temperature, pH, extrusion, baking and frozen before eating, have significant effects on the bioavailability of cereal β-glucans, hence, its ability to reduce blood glucose and cholesterol levels.
KeywordsCereal β-glucan Polysaccharide Structure Functional properties Physiological effect
The authors would like to thank Ms. Cathy Wang and Mr. Xiaoqing Huang for their technical support.
- 1.Talk Paper FDA (1997) FDA allows whole oat foods to make health claim on reducing the risk of heart disease. T97-5Google Scholar
- 2.FDA News (2006) FDA finalizes health claim associating consumption of barley products with reduction of risk of coronary heart disease. pp 06–70Google Scholar
- 7.Cui W, Wood PJ (2000) Relationships between structural features, molecular weight and rheological properties of cereal β-D-glucans. In Hydrocolloids: physical chemistry and industrial applications of gels, polysaccharides and proteins. Elsevier Science Publishers, London, pp 159–168Google Scholar
- 12.Cui SW (2001) Polysaccharide gums from agricultural products: processing, structures and applications. CRC Press, Boca Raton, pp 103–166Google Scholar
- 15.Cui SW, Wang Q (2006) Structure–function relationships of cereal β-glucans. In: Oral presentation at the 8th international hydrocolloids conference, held in Trondheim, NorwayGoogle Scholar
- 17.Izawa M, Kano Y, Koshino S (1993) Relationship between structure and solubility of (1–3)(1–4)-β-d-glucan from barley. J Am Soc Brew Chem 51:123Google Scholar
- 18.Doublier JL, Wood PJ (1995) Rheological properties of aqueous-solutions of (1 → 3)(1 → 4)-beta-d-glucan from oats (Avena sativa L.). Cereal Chem 72:335Google Scholar
- 20.Kahlon TS, Chow FI, Knuckles BE, Chiu MM (1993) Cholesterol-lowering effects in hamsters of beta-glucan-enriched barley fraction, dehulled whole barley, rice bran, and oat bran and their combinations. Cereal Chem 70:435Google Scholar
- 21.Bourdon P, Yokoyama W, Davis P, Hudson C, Backus R, Richter D (1999) Postprandial lipid, glucose, insulin, and cholecystokinin responses in men fed barley pasta enriched with β-glucan. Am J Clin Nutr 69:55Google Scholar
- 25.Braaten JT, Wood PJ, Scott FW, Wolynetz MS, Lowe MK, Bradleywhite P (1994) Oat beta-glucan reduces blood cholesterol concentration in hypercholesterolemic subjects. Eur J Clin Nutr 48:465Google Scholar
- 29.Vasanthan T (2005) Grain fiber compositions and methods of use. US Patent Application No. 20050208145Google Scholar