Molecular Size Distribution and Amylase Resistance of Maize Starch Nanoparticles Prepared by Acid Hydrolysis

The molecular size distribution of maize starch nanoparticles (SNP) prepared by acid hydrolysis (3.16M H2SO4) and their amylase-resistant counterparts, before and after debranching, was investigated. The weight average molecular weight (M-w) and linear chain length distribution were determined by high-performance size-exclusion chromatography (HPSEC) and high-performance anion-exchange chromatography (HPAEC), respectively. The objective was to understand the role of amylose involvement in the formation of SNP showing different crystalline structures (A-and B-types). The HPSEC profiles of SNP before debranching from waxy, normal, and high- amylose maize starches showed broad monomodal peaks. Debanched SNP from waxy maize eluted in a single narrow peak, whereas those from nonwaxy starches showed a multimodal distribution. Similar trends were also observed for the chain length distribution patterns, for which the longest detectable chains (degree of polymerization [DP] 31) in waxy maize were significantly lower than those of nonwaxy maize starches (DP 55-59). This indicated the potential amylose involvement in the SNP structure of normal and high amylose starches. Further evidence of amylose involvement was ascribed to the resistance of SNP toward amylolysis (Hylon VII > Hylon V > normal > waxy). The amylase-resistant residues of SNP from high-amylose maize starches were composed of both low Mw linear and branched chains.