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 gran ules (corn, rice, and potato) was investigated by microscopic observat ion, X-ray diffraction, and measurement of specific gravity. Corn star ch granules clearly showed the swelling, disappearance of polarization cross, and destruction of the A-type X-ray diffraction pattern by hig h-pressure treatment at 500 MPa for 20 min. A faint B-type X-ray diffr action pattern appeared simultaneously with this change. In contrast, potato starch granules retained the native granular features and incre ased the B-type X-ray diffraction pattern, even after application of p ressure up to 500 MPa for 60 min. Pressure application with hexane in place of water never changed X-ray diffraction patterns of starches, s o the changes of the crystalline structures of pressure-treated starch es may absolutely require the presence of water. Rice starch also show ed changes similar to those of corn starch. For corn and potato starch granules, either untreated or pressure-treated, the higher the relati ve crystallinity, the smaller the specific gravity.