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Formation and amylase resistance of a novel nano-particulate fraction obtained by acid hydrolysis of normal, hylon V and VII maize starches.
M. PEREZ HERRERA (1), T. Vasanthan (1), R. Hoover (2), M. Izdorczyk (3). (1) University of Alberta, Edmonton, AB, Canada; (2) Memorial University of Newfoundland, St. John’s, NF, Canada; (3) Canadian Grain Commission, Grain Research Laboratory, Winnipeg, MB, Canada

A novel nano-particulate fraction obtained by acid hydrolysis (3.16 M H2SO4, 40°C, 6 days) of maize starches of varying amylose content was characterized. This is the first study that has shown the presence, type and mechanism of formation of nano-particulates during hydrolysis of normal and high amylose maize starches. The objective was to study the molecular composition and morphology of nano-particulates (F2) in order to better understand whether amylose content per se and/or their extent of co-crystallization with amylopectin clusters influence their yield and morphology. The starch hydrolysate was separated into 3 fractions: a) acid solubilized starch (F1), b) acid resistant nano-particles (F2) and c) acid resistant residue (F3). F2 was detected only in normal and high amylose starches, with their yield proportional to amylose content. Scanning electron microscopy revealed the presence of discrete square/ oval/ asymmetrical shaped particulates of diameters in the range 50 to 250 nm in F2. X-ray diffraction pattern of F2 were identical to their native counterparts. The absence of F2 in waxy maize when considered along with the F2 data on normal and high amylose starches provided evidence of the presence of disordered amylopectin starch blocklets and retrograded crystalline amylose in F2. The resistance of nano-particulates in F2 towards amylolysis as determined by the Megazyme method followed the order: hylon VII > hylon V > normal. The residue (RS3) left after hydrolysis ranged in size from 50 to 200 nm in the normal and high amylose maize starches. Studies are underway to determine the molecular size distribution of F2 and the RS3 residues.

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