Physical Properties of Water-Soluble Pentosans from Different Wheat Varieties' (1991)

Cereal Chem. 68(2): 145-150 The physical properties of water-soluble pentosans and their assessed by the storage modulus (G') and tan6 (G/G'), were obtained constituents, arabinoxylan and arabinogalactan, in solution or gels, were for the preparations derived from Katepwa, followed by those from HY investigated using purified preparations from flours of eight wheat 355, HY 320, and Fielder. Relatively weak gels were obtained for pentosans varieties: HY 355, HY 320, Oslo (Canada prairie spring), Glenlea (Canada from Oslo, Marshall, Norstar, and Glenlea. The storage modulus of utility), Fielder (Canada western soft spring), Norstar (Canada western arabinoxylan and pentosan gels (2%, w/v) were positively correlated with hard red winter), Katepwa (Canada western red spring), and Marshall the intrinsic viscosity of the polymers (r = 0.85 and r = 0.83, respectively; (a hard red spring variety unregistered in Canada). The intrinsic viscosities P < 0.01). Cross-linked pentosans and arabinoxylans held up to 100 for arabinoxylans and arabinogalactans ranged between had ranges of g of water per gram of carbohydrate. Although both arabinoxylans and 2.82-4.20 dl/g and 0.045-0.062 dl/g, respectively. Oxidative gelation of arabinogalactans reduced the surface tension of water, only arabinoxylans 2% (w/v) pentosan and arabinoxylan solutions (H 2 02 and peroxidase) effectively stabilized protein foams on heating. was probed by dynamic rheometry. The most rigid gel networks, as Water-soluble pentosans of wheat exhibit some unique physical properties that have been the subject of many studies. The ability to bind large quantities of water (Bushuk 1966) and to form viscous solutions or gels via covalent cross-linking (Geissmann and Neukom 1973), are important attributes that also can have direct functional implications during mixing, dough development, and baking of bread. Although the water absorption properties of native pentosans have been reported in previous investigations (Jelaca and Hlynka 1971, Patil et al 1975), no studies have been done on water absorption of isolated cross-linked pentosans and their polymeric constituents. The water-holding capacity of polymerized pentosans probably would affect the distribution of moisture among dough constituents and thereby alter the rheological properties of dough systems. Of the many reports on different aspects of gelation of wheat pentosans (Neukom and Markwalder 1978, Hoseney and Faubion 1981, Crowe and Rasper 1988, Izydorczyk et al 1990), only one (Ciacco and D'Appolonia 1982) suggested that the gelling ability of pentosans depends also on their varietal origin. Another important functional property of fermented dough systems is their ability to hold gas. In fact, air occlusion during the mixing and formation of gas cells during fermentation plays an important role in the rheology of dough and consequently affects the final texture of baked products (MacRitchie 1986). In this respect, dough and bread can be viewed as examples of classic foams. The stability of these systems relates to how gas cells resist rupture on baking, especially during the initial oven heating and before the surrounding fluid network (the viscosity of dough at 600C is only one fifth of its viscosity at 25°C) is transformed into a solid structure. This stability depends on the initial gas distribution, and, most important, on the nature of the compounds stabilizing the film around gas cells. Although the involvement of gluten proteins in film formation is generally acknowledged, evidence also indicates that some polysaccharides, such as xanthan, locust bean, and guar gums possess similar properties (Hoseney 1984, McCleary 1986). This article presents information on the gelling potential and flow behavior of purified pentosans and their constituents in aqueous solutions, as probed by small-deformation mechanical measurements and steady shear rheometry. Furthermore, the surface properties of these polysaccharides are examined in the context of imparting stability to heated foam systems.