Effect of alpha-amylase on the physicochemical and structural characteristics of corn starch before and after high pressure pretreatment

The high-pressure process is a novel non-thermal technology by which food is subjected to a pressure of 100-600 MPa. In this research, the effect of bacterial alpha-amylase on the degree of hydrolysis, crystallinity, morphological and thermal characteristics of natural corn starch before and after high pressure processing (300 and 600 Mpa) was investigated. The results showed that with increasing pressure, the effects of processing on the physicochemical and thermal properties of starch were increased. Also, starches treated with high pressure process were more sensitive to enzymatic hydrolysis. The results of SEM analysis showed that the starches treated with a pressure equal to 600 MPa had the highest porosity, indentation and roughness on the surface of the starch granules and showed the highest sensitivity to enzymatic hydrolysis. The amount of crystallinity in the starches treated with high pressure and enzyme was lower than the natural starch sample due to the destruction of the starch crystal structure. The results of the thermal characteristics of starches showed that with the increase of the applied pressure, the parameters of TO, TP, TC and enthalpy decreased significantly. The high- pressure processing can create favorable physical modifications on the starch, and because of these modifications, a lower amount of alpha-amylase can be used for starch hydrolysis.