IMPACT OF ANNEALING ON THE SUSCEPTIBILITY OF WHEAT, POTATO AND PEA STARCHES TO HYDROLYSIS WITH PANCREATIN

Native, and one- and two-step annealed wheat, pea and potato starches were subjected to hydrolysis with pancreatin (1.34 nKat/mg starch, 37 degrees C, pH 6.0). While annealing increases enzyme resistance for wh eat, pea and potato starches in the first (rapid) phase of hydrolysis, it increases the extent of degradation in the second (slower) phase f or wheat and pea starches. Annealed potato starches, however, are stil l more resistant than native potato starch in the second phase of hydr olysis. Environmental scanning electron microscopy shows that enzymic degradation of wheat starch granules does not proceed uniformly throug hout the granule population, Pancreatin action does not affect differe ntial scanning calorimetry (DSC) gelatinisation characteristics of all studied native and of annealed potato starches, Although enzymic hydr olysis has no great effect on the DSC gelatinisation behaviour of nati ve starches, partial enzymic solubilisation of the granules enhances t he effects of annealing. After 2 and 120 h of solubilisation, DSC ther mograms of annealed wheat and pea starches show somewhat broader peaks with lower enthalpies than those of the corresponding unhydrolysed st arches. C-13 CP/MAS NMR data of extensively (46%) degraded and undegra ded native wheat starch granules show no change in double helix conten t, whereas after 57% solubilisation of one-step annealed wheat starch, a decrease in the proportion of double helices is observed. The C-13 CP/MAS NMR signal at 31 ppm increases by a factor 2.0 for 46% solubili sed native wheat starch, and by a factor 2.3 for 57% solubilised annea led wheat starch, indicating resistance of amylose-lipid complexes to pancreatin hydrolysis. Dissociation enthalpies, however, are higher th an can be predicted from a concentration of complexes. The enthalpy of dissociation of amylose-lipid complexes, after enzymic hydrolysis, in creases more for annealed than for native wheat starch. All the above suggest that, during annealing, molecular changes occur that have an i mpact on pancreatin hydrolysis. (C) 1998 Elsevier Science Ltd.