EFFECT OF HIGH-PRESSURE ON THE CRYSTALLINE-STRUCTURE OF VARIOUS STARCH GRANULES

High-pressure treatment was applied to suspensions of starch and water (1:1, w/v) at 50-500 MPa for 20 or 60 min, and the effect of the high pressure on the crystalline structure of several kinds of starch granules (corn, rice, and potato) was investigated by microscopic observation, X-ray diffraction, and measurement of specific gravity. Corn starch granules clearly showed the swelling, disappearance of polarization cross, and destruction of the A-type X-ray diffraction pattern by high-pressure treatment at 500 MPa for 20 min. A faint B-type X-ray diffraction pattern appeared simultaneously with this change. In contrast, potato starch granules retained the native granular features and increased the B-type X-ray diffraction pattern, even after application of pressure up to 500 MPa for 60 min. Pressure application with hexane in place of water never changed X-ray diffraction patterns of starches, so the changes of the crystalline structures of pressure-treated starches may absolutely require the presence of water. Rice starch also showed changes similar to those of corn starch. For corn and potato starch granules, either untreated or pressure-treated, the higher the relative crystallinity, the smaller the specific gravity.