NEAR-INFRARED SPECTROSCOPIC MEASUREMENTS OF STRUCTURAL-CHANGES IN STARCH-CONTAINING EXTRUDED PRODUCTS

Near-infrared spectroscopy was evaluated as a means of following physi cal and chemical changes in starch during the extrusion cooking of whe at flour tinder the Measurements and Testing Program of the European C ommission. With the use of principal component (PC) and canonical corr elation (CC) analyses, samples could be classified according to the se verity of the extrusion cooking conditions. An interpretation of the s pectra showed that the different processing conditions modified the ph ysical structure of the starch molecules. At low values of specific me chanical energy inputs, starch was partially crystalline and the near- infrared spectra exhibited characteristic absorption bands at about 14 28, 1520, and 1587 nm. As the energy inputs increased, causing a chang e to molten starch, the intensity of the bands at 1520 and 1587 mn dec reased, with a shift of the 1428-nm absorption band towards longer wav elengths also being observed. The changes that occurred were thought t o be due to a disruption of the intra- and intermolecular hydrogen bon ding of the starch. At the higher levels of specific mechanical energy inputs, the starch molecules underwent further structural modificatio n, resulting in their partial degradation.