SHORT-RANGE STRUCTURE IN (PARTIALLY) CRYSTALLINE POTATO STARCH DETERMINED WITH ATTENUATED TOTAL REFLECTANCE FOURIER-TRANSFORM IR SPECTROSCOPY

A fast and direct method, based on infrared spectroscopy, for quantita tive determination of starch short-range structure has been developed. The IR spectrum of starch is sensitive to changes in short-range stru cture in the C-C and C-O stretching region at 1300-800 cm(-1). The IR absorbance band at 1047 cm(-1) is sensitive to the amount of ordered o r crystalline starch and the band at 1022 cm(-1) is characteristic of amorphous starch, The ratios (R) of the heights of the bands at 1047 a nd 1022 cm(-1), which expresses the amount of ordered starch to amorph ous starch, and 1047 and 1035 cm(-1), which is a measure of the amount of ordered starch, showed a linear regression with the amount of pota to starch having B-type crystallinity as determined with wide-angle X- ray diffractometry. The IR spectrum and thus the short-range order is also sensitive to water content. In particular, the band at 994 cm(-1) , which is related to intramolecular hydrogen bonding of the hydroxyl group at C-6, is water sensitive. It is possible to quantify the IR da ta in terms of short-range order (S-IR) over a range of 10-50% water. The method has been applied to quantify the changes in short-range str ucture during the melting of potato starch with 18 or 26% (w/w) water. The amount of short-range structure and the changes during melting in the (partially) destructured starch samples concur with differential scanning calorimetry and wide-angle X-ray diffractometry measurements.