STUDIES OF THE EFFECT OF THE SUGARS RIBOSE, XYLOSE AND FRUCTOSE ON THE RETROGRADATION OF WHEAT-STARCH GELS BY X-RAY-DIFFRACTION

The effects of the sugars ribose, xylose and fructose on the retrogradation of wheat starch gels were investigated by measuring the area under the strong 0.516 nm diffraction peak (characteristic of B-type crystalline retrograded starch) as a function of storage time for a series of gels containing different amounts of added sugars. Retrogradation was monitored as the increase in peak area with storage time. The results obtained suggested that all three sugars altered crystallisation and hence retrogradation of the gels. For the concentration regimes studied, xylose and ribose acted by progressively reducing crystallisation with increasing sugar concentration. In the case of fructose two effects were noted. The fructose led to an increase in both thermally reversible and thermally irreversible crystallisation upon storage. For xylose and ribose the increase in crystallisation upon storage was almost totally thermoreversible suggesting that the retrogradation upon storage was dominated by amylopectin crystallisation.