Manipulation of the internal structure of high amylose maize starch by high pressure treatment and its diverse influence on digestion

In this study, high amylose maize starch was mixed with different moisture contents, followed by high hydrostatic pressure (HHP) at 200, 400, 600, 800 and 1000 MP, respectively. Changes in starch physicochemical and digestion properties associated with HHP treatment were analyzed in terms of starch granular morphology, lamellar structures and crystalline characteristics. Results showed that, under the same pressure treatments, the starches with different moisture contents exhibited a similar pattern of the changes in the properties. The erosion of digestive enzymes on starch granules was enhanced with increased HPP pressures. Treatment with 200 and 400 MP led to a reduction of digestibility compared to its native one. However, digestion was gradually promoted when the treatment pressure reached up to 600 MP. Structural data acquired from SAXS and WAX indicated the treatment of HHP up to 600 MP partly destroyed the starch granules internally, resulting in a decreased degree of organized structure. These results may reveal the importance of starch lamellar structure and crystalline order as being the key structural parameters for influencing starch digestion properties. Changes in the electron density following the digestion indicated that digestion characteristics of the starch are highly related to the changes in its corresponding internal structure of amylopectin amorphous layer, amylose amorphous and amylopectin crystal layer caused by HPP. Further analysis of the changes in the relative crystallinity of the starch may suggest that starch digestion characteristics are highly related to lamellar structure but not relative crystallinity.