Order in maize mutant starches revealed by mild acid hydrolysis

Abstract

Maize mutants starches cover a broad range of features with respect to apparent amylose content (1–63%), fine structure of amylopectin (short- to long-chain ratios), crystallinity level (19–48%) and polymorphic type (various proportions of A-, B- and V allomorphs). This study subjected starches from single and double maize mutants to mild acid hydrolysis (35 days) with 2.2 N HCl. The crystallinity of these starches before and after 12 days of mild hydrolysis was studied by X-ray diffractometry. The linear chain length distribution of amylopectin and residues was studied after debranching, followed by high-performance anion-exchange chromatography with pulsed amperometric detection. Regardless of amylose content or crystallinity level, starches with a predominant B-crystalline type were less susceptible to acid degradation than others, and initial rates of hydrolysis were lower for B-type than A-type starches. Changes in initial hydrolysis rate may have been due to defective crystallites and/or dangling chains. Branch points were more frequent in residual fractions of A-type starches (normal, wxdu) than in predominant B-type starch ( aewx). Conversely, residual fractions of a pure B-type starch ( ae) appeared to have no branch points, suggesting the involvement of apparent amylose in crystallites.