Annealing of maize starches at elevated temperatures

Abstract

Maize starches were annealed in excess water at temperatures from 50 to 70.degree. C by a multistep process, which allowed higher annealing temperatures than could be obtained by single-step annealing, without gelatinizing starch granules. Gelatinization of the annealed samples was then studied by differential scanning calorimetry. Annealing of normal and waxy maize starches increased the onset and peak temperature, with relatively little change in gelatinization enthalpy. Amylomaizes increased dramatically in enthalpy, and the endotherms became more distinct as annealing temperature increased. This change in gelatinization characteristics is interpreted as evidence that interaction between amylose and amylopectin occurs in amylomaize granules during annealing. These differences in interaction are consistent with differences in crystal structure; A-type crystals of normal and waxy starch are relatively stable, and amylose and amylopectin domains appear to be separate. Amylomaize starches contain B-type crystallites, which are energetically more likely to reform, possibly to give A-type structures. The B-type starches are considered to have a higher degree of intermingling of amylose and amylopectin, which allows more extended interaction during annealing, resulting in increased gelatinization enthalpy.