Physicochemical changes of maize starch treated by ball milling with limited water content

Abstract

A granular maize starch with limited amounts of water was ball milled, and the structural changes were investigated. The chemical changes were analyzed in terms of amylose content, hydroxyl and carbonyl contents, and intrinsic viscosity. The granule or aggregation structures were characterized by X‐ray diffraction, differential scanning calorimetry, laser particle diameter analyzer, and scanning electron microscope. The gelatinization and paste property were measured with a Rapid Visco‐Analyzer. Under the ball‐milling conditions of 25 wt% water content based on the starch, a ball diameter of 15 mm, a weight ratio of ball to starch at 4:1, and milling time of 3 h, the ball‐milled starch granules did not have apparent gelatinization or agglomeration. After the ball milling, the system temperature increased by 25.5°C. The resultant starch granules displayed a flat‐ or oval‐shaped pattern without edges, and their particle size slightly increased with a narrower size distribution. The ball‐milled starch was mildly oxidized, and the intrinsic viscosity and the amylopectin content decreased a little. The crystallinity of granules decreased greatly from 31.1 to 13.0%, concurrent with a decrease in the thermal transition enthalpy. The pasting temperature increased, while the peak viscosity, breakdown, and setback greatly decreased. Our results indicated that the limited additional water in the ball‐milling process helps expand the amorphous region in starch granules and could reduce damage level of starch molecules and granules.