A COMPARATIVE-STUDY OF THE EFFECT OF SUGARS ON THE THERMAL AND MECHANICAL-PROPERTIES OF CONCENTRATED WAXY MAIZE, WHEAT, POTATO AND PEA STARCH GELS

A comparative study was undertaken to examine the effect of sugars on the thermal and mechanical properties of ageing waxy maize, wheat, pot ato and pea starch gels. The addition of sugars, at a ratio of 1:0.5:1 .5 (w/w) for starch-sugar-water mixtures, inhibited chain reorganizati on in starch gels, as followed by differential scanning calorimetry an d dynamic rheometry in the order, ribose > sucrose > maltotriose > wat er alone, glucose > fructose. Kinetic experiments on the evolution of storage modulus (G') at 8 degrees C indicated a progressive transition from a sigmoid curve (waxy maize) to a hyperbolic G' - time relations hip (potato and pea starches), consistent with an increasing proportio n of amylose in the composite gels. The effects of sugars on the devel opment of the retrogradation endotherm (Delta H) and gel rigidity (G') were less pronounced for potato and pea starches than for waxy maize or wheat starches, presumably because of their higher amylose content, which dominates the gel network properties.