The Preparation And Characteristics Of Slowly Digestible Starch

Starch was one of the major renewable and biodegradable biopolymers, the yield of maize in China ranked the second in the world. Slowly digestible waxy maize starch, which was prepared based on waxy maize starch as raw materials through octenyl succinic anhydride esterification and a subsequent hydrothermal treatment, will promote the development of the starch research towards starch nutrition and health with positive economic and social effects.Human blood sugar and insulin levels are closely related to the occurrence of obesity, diabetes,and cardiovascular disease. The glucose response, which can be predicted from carbohydrate digestion rate, plays an important role in blood glucose homeostasis. This study established an in vitro method to evaluate the rate and extent of starch hydrolysis , and the content of slowly digestible starch (SDS) was measured by the method.In this study, both single-factor and response surface designs were used to optimize the preparation of OSA modified waxy maize starch. The optimum condition was: isopropanol as a diluent with six-fold dilution,3% OSA, reaction time 2.3h,pH 8.4, and temperature of 35℃. The in vitro test of the OSA modified waxy maize starch (OSA-starch) showed that, correlated to the degree of substitution (DS) up to 0.0237, the rapidly digestible starch (RDS) decreased from 84.2% to 53.1% , whereas the slowly digestible starch (SDS) and resistant starch (RS) increased from 15.7% to 28.3% and from 0.1% to 18.6%, respectively. Hydrothermal treatment of OSA-starch further increased its SDS content, and an optimum combination of temperature (120°C), moisture (10%) and time (4 hr) to produce the highest SDS content (43.8%) was obtained using a response surface methodology.The results of the in vivo human glycemic response experiment showed that slowly digestible starch lowered blood glucose peak lever and also delayed the peak time, which provides a good basis to further application of the prepared slowly digestible starch.Gel permeation chromatography analysis of the debranched OSA waxy maize starch showed that OSA modification mainly occurred at the branching regions of the amylopectin molecules, and amylopectin fragmentation after additional heat treatment might lead to an increase of SDS by concomitantly decreasing the content of RS. Enzyme kinetics results, based on the Michaelis-Menten kinetic model, showed a simultaneous decrease of Km and Vm when the modified starch sample was digested by eitherα–amylase or amyloglucosidase, indicating an uncompetitive inhibition of the enzyme activity by the modified starch molecules. Both the uncompetitive inhibition and amylopectin fragmentation contribute to the slow digestion property of the modified waxy maize starch.