When using chemically modified starches, one has to be aware that they tend to retrograde rapidly. Retrogradation is a non-reversible process where the hydrated amylose molecules form hydrogen bonds between one another when the solution is cooled. The chains of amylose wrap around themselves as double helices, forming colloidal crystallites (Imberty et al. 1991). If the solution is dilute, particulate precipitation occurs whereas if the solution is more concentrated a network structure, a gel, is formed. The gel formation process in concentrated solutions is faster than the precipitation process in dilute solutions (Wurzburg 1986). The rate of retrogradation depends on several factors including starch concentration, degree of hydration, molecular weight, salt concentration, temperature, time, and pH. Naturally occurring contaminants, like lipids (Godet et al. 1993a), can form inclusion complexes with the amylose molecule and initiate or speed up the retrogradation process. The retrogradation must not be confused with the phase separation induced by the interaction of hydrophobic functional groups. Such a phase separation in starches is fully reversible, whereas retrogradation is a non-reversible process. The HM starches used in this work showed no retrogradation during the course of the experiments.
