Enzyme susceptibility of high-amylose starch precipitated from sodium hydroxide dispersions at different precipitation conditions

While a number of resistant starch (RS)-containing ingredients are commercially available today, there appear to be no starch products designed with the goal of reducing the rate of digestion of the non-RS portion. No method has been published to quantify the digestion rates of starch. Current methods to enhance the RS content of starch use the structures inherent to granules as templates for development of new structures. Formation of new structures is limited by the structures used as templates. There is currently no practical method to disperse HAMS which is necessary to overcome constrains due to inherent structure in order to then manipulate the enzyme susceptibility in new ways. The overall goal of this project was to use precipitation of sodium hydroxide dispersed starch to produce non-granular starch material with a range of enzyme susceptibilities, and to relate enzyme susceptibility to physical structure.; Starch was precipitated using either ethanol or ammonium sulfate. Mixtures of isolated linear and branched fractions were precipitates to test the effect of branched material on enzyme susceptibility The official method for in vitro RS determination (AOAC 2002.02, AACC 32-40) was modified to allow analysis of small samples for determination of RS and digestion timecourse.; Precipitates prepared with ethanol had lower RS values than precipitates prepared with ammonium sulfate at the same precipitation temperature and starch concentration. The precipitates prepared from linear fraction had the highest RS values (54% for ammonium sulfate, 29% for ethanol) and lowest proportion of substrate 1 (29% for ammonium sulfate precipitate, 69% for ethanol precipitate), but the relationship between linear proportion and enzyme susceptibility was found to be complicated.; The difference in enzyme susceptibility might be explained by a combination of type of crystallinity and morphology. Ethanol precipitates had crystalline (V-type) and non-crystalline single helices compared to the double helices (B-type) of the ammonium sulfate precipitates. The change of single helical to double helical conformation upon re-hydration as well as the more porous morphology of the ethanol precipitates might explain the higher enzyme susceptibility of the ethanol precipitates.