Study of the aging and oxidation processes of vinegar samples from different origins during storage by near-infrared spectroscopy

Near infrared spectroscopy combined with several chemometrical techniques has been used to control the aging process in vinegar and the changes produced during storage. Several considerations regarding NIR instrument changes, which can add noise to the determinations, were made and a strategy based on the correction of the spectra was used to eliminate the differences between spectra due to instrument variation, in particular to lamp change. Ninety-five different vinegars were measured using a near-infrared spectrometer. The spectrum of each vinegar sample was collected twice: the first time as soon as the bottle was opened and the vinegar had not undergone any oxidation process and the second measurement was taken after a certain period of time. Then, in order to quantify the discrimination between the two groups of spectra recorded in the two occasions and so to estimate the aging effect in the vinegar samples, Linear Discriminant Analysis was used as a classification method. To improve the results, bearing in mind that many of the measured variables could be useless and that the elimination of these wavelengths can help in interpretation, a feature selection technique was applied. For chemical interpretation of the retained wavelengths, the spectral zones correlated with the aging process were isolated and the species and compounds that can absorb in these NIR spectra bands were studied. (c) 2005 Elsevier B.V. All rights reserved.