PHYSICAL CHARACTERIZATION OF AMYLOPECTIN GELS

Amylopectin is a highly and non-randomly branched polysaccharide and is one of the two main components of starch. Aqueous amylopectin solutions of sufficiently high concentration can form physically cross-linked thermoreversible gels upon cooling to below room temperature. We present a detailed investigation onto the reheology of these gels and establish the relationship between gel modulus and concentration; this is fitted with the model of Clark and Ross-Murphy. Amylopectin gelation is accompanied by the development of crystallinity. Differential Scanning Calorimetry (DSC) and novel time-resolved Wide Angle X-ray Scattering measurements using synchrotron radiation indicate that the DSC gel melting endotherm provides a measurement of the degree and perfection of the crystallinity in the gel. For gels stored at 4-degrees-C, the crystallinity covered a wide range of perfection and part of the contribution to the growth in the melting endotherm was the result of the formation of a disproportionate number of poorer, less perfect crystallites. Annealing amylopectin gels below their peak melting temperature, following storage at 4-degrees-C increased the perfection of the crystallinity by melting out the poorest crystallites, causing the gels to melt at a higher temperature and over a narrower range.