Effect and mechanism of ultrahigh hydrostatic pressure on the structure and properties of starches

Normal maize, waxy maize, high-amylose maize VII, tapioca, potato, and rice starches were ultrahigh hydrostatic pressurized at 690 MPa. Structures and properties of the pressurized starches were investigated. Each starch was pressurized in powder form, in 1/1 (v/w) ethanol/starch suspension, and in 1/1 and 2/1 (v/w) water/starch suspensions for 5 min and 1 h dwelling times. The crystalline structure, thermal and pasting properties, molecular weight distributions, and morphology of starch granules were analyzed. X-ray diffraction studies showed that the ultrahigh pressure converted starches that displayed the A-type X-ray patterns to the B-type-like pattern. Differential scanning calorimeter thermograms of starches taken right after the pressure treatments showed a newly developed peak that resembled that of the retrograded (B-type) starch. Crystalline structures of starches that displayed the B-type pattern, however, were not changed by the pressure treatments in a water suspension. The ultrahigh hydrostatic pressure did not change the molecular weight distribution of the starch. The pressurization of starches in powder form and in the presence of alcohol resulted in a reduction in peak intensity of the X-ray pattern but no conversion from the A-type to the B-type.