ABSTRACT
The objective of the present study was to identify physical, chemical, and physicochemical mechanisms at the origin of the NIR spectra modifications recorded during dough mixing. An FT-NIR spectrometer over the 1000–2500 nm range with a fiber optic probe in contact with the dough during processing was used. The NIR spectra collections are analyzed as raw spectra and after second derivative treatment by using principal component analysis (PCA). The analysis of the three first principal components describe high cumulative variance (>95%). The PCA on the raw NIR spectra demonstrate the dominant contribution of physical mechanisms (granular state and surface aspect of the dough) and, to a lesser extent, of physicochemical mechanisms (water and protein modifications). The PCA of the second derivative spectra on the 1000–2325 nm wavelength range and on restricted wavelength ranges (1352–1485 nm, 1778–2052 nm, or 2109–2325 nm) allowed a physicochemical description of the NIR absorbance variations. The NIR absorbance variations mainly arise from the 1778–2052 nm range related to the O-H vibrations. NIR mixing times were determined from the PCA score plots based on raw and second derivative NIR spectra and were associated with changes in different dough physicochemical properties (glutenin depolymerization rate, extractable liquid phase, consistency, maximum strain, and stress at break).
