Interactions of potato starch with selected polysaccharide hydrocolloids as measured by low-field NMR

Relaxation times of water molecules in binary potato starch gels with Arabic, carob, guar, karaya.. and xanthan gums as well as 1 and kappa-carrageenans were measured. On heating 5% aqueous suspension of potato starch up to 55 degrees C, relaxation times T-1 and T-2 increased, that is, molecular dynamics of water molecules rose as the consequence of producing disorder in solution on elevating temperature. However, beginning from 55 degrees C T-1 decreased as a consequence of gelation and, hence, immobilization of water molecules in the gel formed. After passing the point of gelation, T-1 almost monotonously rose up to the end of the measurement range (96 degrees C). Admixture of plant gums qualitatively and quantitatively perturbed these tendencies but did not reverse them. Gelation of starch in aqueous gum solution first involved conformational changes in polysaccharides. They proceeded until temperature of gelation was achieved. After that, formation of polymeric network took place. The course of gelation was controlled by water availability. The latter depended not only on the ability of particular gums to hold water molecules but also on their conformational changes and inhibition of gelation resulting from the interactions between gums and starch granules. (C) 2007 Elsevier Ltd. All rights reserved.