Freeze-Thawing Assisted Preparation of Acid-Hydrolyzed Starch: Microstructure and Physicochemical Properties

The modification of starch by a single freeze-thawing process and acid hydrolysis has been reported, while the combination of freeze-thawing and acid hydrolysis on the microstructure and physicochemical properties is unknown. The present study investigates the supporting effect of freeze-thawing pretreatment by comparing single modifications with the corresponding freeze-thawing assisted acid hydrolyzed starch in terms of granular, physicochemical, and thermal properties. Starch samples treated by combined treatment show the most severe damage on the surface and the oil adsorptive capacity is enhanced from 69.7% to 109.4%. In addition, the solubility of starch granules is notably improved by 35.9% and the swelling power decreases by 39.7% via the combined treatment, respectively. The results of Fourier transform infrared spectroscopy and X-ray diffraction indicate that in comparison with native corn starch, the chemical groups of modified starch processed by combined treatment are not altered, while the relative crystallinity significantly increases from 31.4% to 33.9%. Significant changes in the thermal effects are attributed to molecular rearrangements after hydrolysis of amylose in the amorphous regions. Therefore, the combined treatment would be an efficient and useful method to prepare functional starch.