Effects of the combination of freeze-thawing and enzymatic hydrolysis on the microstructure and physicochemical properties of porous corn starch

The effects of the combination of freeze-thawing and enzymatic hydrolysis on the microstructure and physicochemical properties of porous corn starch were investigated. The combined treatment produced more pores in each starch granule than either individual treatment, as revealed by scanning electron microcopy (SEM). Consequently, this porous starch treated by combined treatment increased adsorptive capacity for water and oil, swelling power and solubility, that the openings and cavities induced in starch granules by freeze-thawing enhanced the susceptibility of starch to enzymatic digestion. Compared to native starch, the particle sizes decreased, while the crystallinity and gelatinization enthalpy of starch processed by the combined treatment increased, as determined by Fourier Transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. The values of particle size, crystallinity and gelatinization enthalpy for starch processed with the combined treatment were intermediate to those of starch processed with either freeze-thawing or enzymatic hydrolysis. While the particle size was higher than that of native after freeze-thawing but the obviously decreased after enzymatic hydrolysis. The crystallinity and enthalpy of starch decreased from 15.51 to 4.19 J/g to 14.65% and 4.12J/g after freeze-thawing but increased to 16.09% and 4.74J/g after enzymatic hydrolysis. Enzymatic hydrolysis causes opposite and more severe changes to the starch granule compared with freeze-thawing. The variation in pasting viscosities by combined treated revealed the water was easy to enter starch by the pores on the surface. In brief, the combined treatment is an attractive alternative for obtaining porous corn starch.