Structural properties of starch in bread and bread model systems: Influence of an antistaling alpha-amylase

The influence of an antistaling a-amylase on bread crumb and on wheat starc h gels was investigated taking into account different levels of structural hierarchy. Bread was prepared by a conventional baking procedure. Starch ge ls were produced by heating a concentrated starch dispersion in closed mold s. Bread and starch gels were characterized by compression tests, light mic roscopy (LM), differential scanning calorimetry, and Xray measurements. The a-amylase enhanced the initial firmness of starch gels and reduced the fir ming rate of bread and starch gels on aging. LM revealed that amylose and a mylopectin phase-separated within the starch granules and that freshly bake d control bread and starch gels showed weak birefringence which became more intense during aging. Amylase-containing bread and starch gels exhibited s trong birefringence in the amylose rich region of the granules directly aft er baking which did not significantly increase during aging. The enzyme hin dered the retrogradation of amylopectin as detected by differential scannin g calorimetry, whereas X-ray diffraction indicated that the enzyme induced low levels of starch crystallinity which did not change during aging. It is hypothesized that the antistaling effect of the amylase is based on the ca pacity to partially degrade amylopectin and, by this, to hinder its recryst allization. On the other hand, the enzyme slightly degrades amylose by an e ndo-mechanism which, in turn, promotes the rapid formation of a partly crys talline amylose network in fresh bread and hinders amylose rearrangements d uring aging.