RHEOLOGICAL PROPERTIES OF WATER-SOLUBLE NONSTARCH POLYSACCHARIDES FROM WHOLE GRAIN RYE FLOUR

The typical properties of the dough and the characteristic structure of the bread crumb are the result of the interaction of many components. The water soluble non-starch polysaccharides of rye (rye-WSNSP), consisting mainly of pentosans, form viscous solutions and gels in the presence of oxidizing agents. A considerable decrease in the viscosity following the addition of endo-xylanase shows that an intact arabinoxylan moiety was necessary to retain the viscous properties of the rye-WSNSP solutions in water. The presence of the oxidizing (H2O2/peroxidase) agent in the aqueous rye-WSNSP solution (6.0 mg/ml water) caused an increase (5.5X) in the viscosity. Ferulic acid (3% w/w) and cysteine (3.7% w/w) on the other hand, restricted the increase in oxidative viscosity by 60 and 35% respectively. The flow curves showed that the rye-WSNSP solutions were shear thinning. The relationship of shear stress and shear rate was analysed using the Ostwald equation tau = k gamma(n). The values for the flow behaviour index (n = 0.45 - 0.72) were <1 for all the solutions confirming a pseudoplastic flow behaviour. The consistency index (k) increased with the addition of the oxidizing agent to the rye-WSNSP solution and it decreased with the addition of ferulic acid. The presence of rye-WSNSP (0.5% and 0.8%) increased the consistency of wheat flour dough in the farinograph by 30 and 86% respectively and the initial stress relaxation modulus (G(0)) by 37 and 160% respectively. A gradual increase of the dough consistency as well as the initial stress relaxation modulus (G(0)) with an increase in oxidizing agent, in the presence of 0.5% rye-WSNSP, was observed. The half relaxation time (t(1/2)) of the standard dough, taken at G(0)/2, decreased by 12% following the addition of 0.8% rye-WSNSP. However, the oxidative (H2O2/peroxidase) gelation of the wheat dough containing rye-WSNSP (0.5%) increased the half relaxation time (t(1/2)) by 14%.