Characterization of Maize Starch Nanoparticles Prepared by Acid Hydrolysis

Starch nanoparticles (SNP) from maize starches of varying amylose content (0-71%) were prepared by acid hydrolysis (3.16M H2SO4, at 40 degrees C up to 6 days) followed by repeated water washings. During the washing cycles, nonwaxy starches (normal, Hylon V, and Hylon VII) had suspended particles in the water washings, which were not evident in waxy starch. Microscopic examination revealed the presence of SNP in the cloudy supernatants of nonwaxy starches and in the final washed residue of waxy maize. The objective of this study was to collect SNP fractions accordingly and determine whether variation in the native starch amylose content would influence the yield, morphology, and crystallinity of the SNP. In nonwaxy starches, the yield of SNP increased up to 26.6% with hydrolysis time and was proportional to the amylose content. Morphology of SNP differed with starch type: flat/elliptical (500 nm) in waxy, oval/irregular (50-200 nm) in normal, oval/round (40-50 nm) in Hylon V, and square/polygonal (50-100 nm) in Hylon VII. X-ray diffraction confirmed the presence of A-type crystals in SNP from all starch types and a crystalline transformation from B-to A-type in Hylon starches. The relative crystallinity of SNP was higher than their native starch counterparts.