Physicochemical Properties and Digestibility of Malate Corn Starch

Malate corn starch is one kind of modified starch by the esterification of malic acid (organic acid) with corn starch,which has some similar functional characteristics of dietary fiber.In this study,L-malic acid and corn starch were used as raw materials to prepare malate starch by the dry heat treatment at high temperature.This work aims to elucidate the differences between the physicochemical characteristics of malate starch and corn starch,such as its apparent structure,gelatinization,swelling and in vitro digestibility characteristics.The changes of apparent structure and physicochemical properties of malate starch with different degrees of substitution were clarified,and the samples were analyzed by X-ray diffraction (XRD),scanning electron microscopy (SEM) and infra-red spectroscopy (FT-IR).The results showed that,compared with the corn starch,the whiteness,swelling,freeze-thaw stability and gelatinization of malate starch decreased.In SEM,more small starch fragments were observed in the malate starch with low degree of substitution.With the increase of the degree of substitution,the surface of starch became rough and holes appeared,and the particle shape became irregular,finally the adhesion between fragments was observed.The X-ray diffraction pattern of the corn starch and the malate starch with low degree of substitution showed that the crystal was A-type crystal.However,as the degree of substitution increased,the crystal structure was destroyed,and the diffraction peak became weaker and finally disappeared.The results of FT-IR indicated that the characteristic peak of carbonyl vibration appeared in the esterified starch at 1 739 cm^-1,and the peak value increased obviously with the increase of the degree of substitution.In vitro digestion experiment showed that the content of resistant starch increased obviously after the esterification.