Cereal Pentosans: Their Estimation and Significance. IV. Pentosans in Wheat Flour Varieties and Fractions

Cereal Chem. 65(3):182-185 Total and water-soluble pentosans were determined in flours milled from absorption and soluble pentosans were correlated, and the correlation hard red winter, hard red spring, and soft red winter wheat cultivars grown coefficient increased if the results were expressed on a constant protein at various locations and environments; in two sets of commercial airbasis. In air-fractionated flours, protein and pentosan contents were fractionated flours; and in gluten, starch, and water solubles separated correlated positively. Pentosan contents of three flours were related to from flours that varied in pentosan contents. There was a negative yields of gluten and prime starch. correlation between protein and soluble pentosan contents. Water The role of pentosans in bread and dough was reviewed by D'Appolonia (1971), and some developments in research on wheat flour pentosans were reviewed by D'Appolonia and Kim (1976). Jelaca and Hlynka (1972) reported that water-soluble pentosans increase resistance of doughs to extrusion. The effect of pentosans was likened to that of iodate. It was postulated that the mechanism producing the pentosan effect likely involves an interaction between gluten and pentosan polysaccharides. Pentosans associated with gluten were shown by D'Appolonia and Gilles (1971) to be similar to pentosans extracted from flour by water. Pentosans extracted from durum glutens had a greater degree of branching as well as a higher intrinsic viscosity than pentosans extracted from hard red spring (HRS) and soft wheat flour glutens. Total water solubles and water-soluble pentosans were isolated from pin-milled and air-classified fractions of selected flour streams from three cultivars of HRS wheat (MacArthur and D'Appolonia 1977). The high-protein flour fraction contained the highest amount of water-soluble pentosans. Variations in pentosan contents were not responsible for bromate requirements in studies conducted by Marais and D'Appolonia (1981). Patil et al (1976) had previously shown that water-soluble pentosans are required to obtain normal loaf volume and that pentosans and bromate, in the absence of other watersoluble components, have an additive effect of overoxidation that causes dough rigidity and reduces loaf volume. It was postulated that rigidity of reconstituted doughs containing pentosans and bromate (and usually characterized by reduced loaf volume) possibly results from a combination of two factors: 1) removal of water-soluble components responsible for gluten-protein extensibility and/ or for oxidation requirement (for suppressing the detrimental effect of overoxidation), and 2) oxidation of the pentosan-glycoprotein interaction product. Previous studies from our laboratories described estimation of pentosans in whole wheat and laboratory-milled wheat products by the orcinol HCO method (Hashimoto et al 1987a). The method was used to estimate pentosans in whole grains, laboratory abraded grains, and pearlings from abraded grains; in commercial samples of brewers' dried grain; and in grain and hulls from cereal 'Research food technologist and research chemist, respectively, U.S. Grain Marketing Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 1515 College Avenue, Manhattan, KS 66502. Mention of firm names or trade products does not constitute endorsement by the USDA over others not mentioned. 2Visiting scientist, present address: Nakamura Gakuen College, Befu, Fukuoka, Japan. 'Present address: Washington State University, Dept. of Food Science and Human Nutrition, Pullman 99164-2032. grains (Hashimoto et al 1987b). Pentosans were estimated also in 79 hard red winter (HRW) wheat flour samples representing varietal composites from several locations from three nurseries (Shogren et al 1987). Correlation coefficients among varieties between water-soluble pentosan and protein contents were negative and, generally, significant. Incorporation of a watersoluble pentosan into equations containing a protein content term significantly increased the multiple correlations with water absorption and, to a lesser degree, with loaf volume and mixing time. The negative correlations between protein and soluble pentosans were established for composite samples (from many locations) of a great number of varieties. The results suggested the need to determine the relationship between protein and pentosan contents, as they affect breadmaking properties and as they relate to various flour fractions, within a variety. We report here on the results of such studies. MATERIALS AND METHODS Three HRW wheat cultivars (Newton, TAM-101, and Scout 66) were grown in Manhattan, KS, in 1981 and 1982. Two HRW wheat cultivars (TAM-107 and TAM-108) were grown in 1985 at 11 locations throughout the Great Plains. Ten samples of HRS wheats harvested in 1985 were obtained from V. L. Youngs and B. L. D'Appolonia (Fargo, ND), and nine samples of SRW wheats harvested in 1986 were obtained from P. L. Finney (Wooster, OH). The wheats were milled on an Allis-Chalmers experimental mill to produce flours of 68-72% extraction that contained about 0.4% ash. Centurk 78, an HRW wheat harvested in 1984 in Colby, KS, was milled on an Allis-Chalmers experimental mill as described by Finney and Bolte (1985). The milled products were combined to provide a wide range of products ranging in ash contents from 0.38 to 5.55%. Two sets of air-classified flours were from commercial sources; one contained four samples and the other six samples. Three flours were separated into gluten, prime starch, tailing starch, and water-soluble fractions according to the procedure described by Finney (1971). These flours were selected to include a high-pentosan sample (TAM-101 composited from several locations in Texas in 1983); an intermediate-pentosan sample (RBS-78, a composite of flours milled from many wheat varieties from many locations throughout the Great Plains, USA); and a low-pentosan sample (NE-Experimental, from an experimental wheat selection composited from several locations in Nebraska in 1983). Protein contents (%) and bake absorptions (%) were 12.3 and 65.0, 12.1 and 60.5, and 12.3 and 55.0 for TAM-101, RBS-78, and the NE-Experimental, respectively. Commercial starch, prime starch, and tailing starch were from Manildra Milling Corp., Shawnee Mission, KS. Pentosan determinations were made as described by Hashimoto 182 CEREAL CHEMISTRY This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1988. et al ( 1987a) and functional (breadmaking) properties as described by Shogren et al (1987). Ash and protein were determined by the AACC methods 08-01 and 46-10, respectively (AACC 1984). All determinations were made at least in duplicate, and all results were averaged. Significance at the 10, 5, and 1% levels is indicated (*, * and ***, respectively). RESULTS AND DISCUSSION Water-soluble pentosans and total protein in flours from three HRW wheats from two crop years are compared in Table I. The soluble pentosans for each variety were fairly constant even though the protein contents varied widely. Previous studies (Shogren et al 1987) indicated that flour from TAM-107 is higher in soluble pentosans than flour from TAM-108. Pairs of TAM-107 and TAM-108 were obtained from 11 locations, and their soluble pentosans and protein contents were determined. The previously observed higher soluble pentosan content for TAM-107 was confirmed (Fig. 1). Negative correlations were obtained for the relation between protein and pentosan contents for TAM-107 (r = -0.381), forTAM-108 (r=-0.575*), andforthetwocombined (r= -0.369*). When the soluble pentosan content was plotted versus TABLE I Protein and Water-Soluble Pentosans in Flours of Three Hard Red Winter Wheats from Two Crop Years Variety and Proteina Water-Soluble Crop Year (N X 5.7, %) Pentosansa (%) 1981 Newton 18.0 0.79 TAM 101 18.9 1.10 Scout 66 17.8 0.85 1982 Newton 9.3 0.77 TAM 101 10.8 1.12 Scout 66 10.3 0.81 a14% moisture basis.