Near-Infrared Spectroscopic Measurements of Structural Changes in Starch-Containing Extruded Products

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Abstract
Near-infrared spectroscopy was evaluated as a means of following physical and chemical changes in starch during the extrusion cooking of wheat flour under the Measurements and Testing Program of the European Commission. With the use of principal component (PC) and canonical correlation (CC) analyses, samples could be classified according to the severity of the extrusion cooking conditions. An interpretation of the spectra showed that the different processing conditions modified the physical structure of the starch molecules. At low values of specific mechanical energy inputs, starch was partially crystalline and the near-infrared spectra exhibited characteristic absorption bands at about 1428, 1520, and 1587 nm. As the energy inputs increased, causing a change to molten starch, the intensity of the bands at 1520 and 1587 nm decreased, with a shift of the 1428-nm absorption band towards longer wavelengths also being observed. The changes that occurred were thought to be due to a disruption of the intra- and intermolecular hydrogen bonding of the starch. At the higher levels of specific mechanical energy inputs, the starch molecules underwent further structural modification, resulting in their partial degradation.