GELATION AND RETROGRADATION OF CONCENTRATED STARCH SYSTEMS .1. GELATION

Small deformation properties of potato and wheat starch suspensions we re studied during heating and cooling at rest by a small amplitude dyn amic rheological test method. Starch concentrations used were 10 to 30 % w/w. The temperature to which the suspensions were heated varied fro m 65 to 90 degrees C. During heating the moduli of the starch systems at first increase and subsequently decrease. On prolonged heating the moduli depend greatly on heating temperature: the higher the temperatu re, the lower the moduli. Properties of concentrated starch systems du ring heating are related to swelling of granules, melting of crystalli tes, separation of amylose from amylopectin and disentanglement of non -covalent bonds. The differences between the rheological properties of potato and wheat starch suspensions are discussed, and compared with those of chemically cross-linked potato starches. Our hypothesis for t he explanation of the observed phenomena is that physical entanglement s or chemical cross-links, naturally or artificially present in starch granules, reduce the swelling capacity of the granules and increase t he stiffness of the swollen granules; as a consequence, the affect the rheological properties of concentrated starch suspensions.