From Chapter 1: Basic Food Science — Oxidation and Reduction
As Hoseney (1984) observed, oxidative gelation is a unique property of the water-soluble wheat-flour pentosans. Baker et al. (1942) first called attention to the ability of soluble pentosans to form a gel when reacting with oxidants. This research attributed part of the pentosans’ dough-improving action to the interaction of gluten proteins with soluble polysaccharides.
Although nonstarch polysaccharides make up only 2 to 2.5% of wheat flour’s constituents (Michniewicz et al. 1990), they exert a powerful influence on dough properties. Addition of 2% of water-insoluble pentosans to a relatively weak flour increased the volume by 30 to 45%. In addition, cell uniformity, crumb characteristics and the elasticity of the bread improved. The pentosans from wheat or rye have also been used to supplement coarse cereals such as millet and sorghum, and bread with improved volume was obtained as a result (Hoseney 1986).
While pentosans are made up of arabinoxylans and arabinogalactans, it is the arabinoxylans that have been specifically investigated for their oxidative gelling ability. Doublier (1990) observed that this ability is related to the presence of small amounts of ferulic acid, which is esterified to the largest part of the arabinoxylan fraction. Neukom (1976) suggested that the gelation mechanism related to crosslinking of arabinoxylan chains through ferulic acid residues, but Hoseney and Faubion (1981) interpreted the linkages as involving covalent binding of protein with the arabinoxylan chain via a ferulic acid group.
Pentosans are even more important to rye bread performance. Rye flour is second only to wheat flour in its ability to retain gas and produce a light loaf of bread, and rye flour contains a much greater amount of pentosans than does wheat flour (Hoseney 1986).
The ratio of pentosans to starch in the rye grain is 1:8. Recent Studies by Weipert and Zwingelberg (1980) have shown that the most important factor in rye-bread baking quality is the pentosan fraction. By blending various streams during rye milling, they found the most favorable ratio of pentosans to starch to be 1:16, and they suggested that because bran and shorts contain 20 to 30% pentosans, these mill streams could be used to supplement the performance of baked foods prepared with non-cereal starches.
Baker, J.C., Parker, H.K., and Mize, M.D. 1942. Cereal Chem. 19: 84.
Doublier, J.-L. 1990. Rheological properties of cereal carbohydrates. In: Dough Rheology and Baked Product Texture. H. Faridi and J.M. Faubion, eds. Van Nostrand Reinhold: New York, NY.
Hoseney, R.C. 1984. Functional properties of pentosans in baked foods. Food Technol. 38 (1): 114.
Hoseney, R.C. 1986. Principles of Cereal Science and Technology. AACC: St. Paul, MN.
Hoseney, R.C., and Faubion, J.M. 1981. A mechanism for the oxidative gelation of wheat flour water-soluble pentosans. Cereal Chem. 58: 421.
Michniewicz, J., Biliaderis, C.G., and Bushuk, W. 1990. Water-insoluble pentosans of wheat: composition and some physical properties. Cereal Chem. 67 (5): 434.
Neukom, H. 1976. Chemistry and properties of the nonstarch polysaccharides (NSP) of wheat flour. Lebensmitt. Wiss. Technol. 9:143.
Weipert, D., and Zwingelberg, H. 1980. The pentosan-starch ratio in relation to quality of milled rye products. In: Cereals for Foods and Beverages. G. Inglett and L. Munck, eds. Academic Press: New York, NY.
More on this topic can be found in “Baking Science & Technology, 4th ed., Vol. I,” Page 43, by E.J. Pyler and L.A. Gorton. Details are found in our store.