UV-VIS spectroscopy for monitoring yogurt stability during storage time

Color, texture and taste are key elements of a consumer's buying decision; thus, monitoring the stability of these features throughout the entire period of yogurt validity is fundamental for dairy product producers. Color, texture and taste deteriorations are due to changes in the physical, chemical and microbiological compositions of yogurt and they can be monitored using lab analyses (especially the microbiological ones) which are expensive and time consuming. In this study, ultraviolet-visible (UV-VIS) spectroscopy was applied as a rapid and alternative technique to traditional analytical methods, to monitor the stability of different commercial yogurt samples up to 49 days of storage at 4 °C. UV-VIS spectroscopy was employed with an integrating sphere for diffuse reflectance measurements and, for each yogurt, color stability during storage time was evaluated in terms of CIEL∗a∗b∗ color space values. Moreover, Partial Least Squares regression combined with Genetic Algorithms (GA-PLS) was performed for predicting the age of the yogurt samples from their UV-VIS spectra. In order to evaluate the texture and taste changes, flow curves and pH values of yogurt during storage were monitored once a week for the entire considered storage period. The UV-VIS and rheological datasets were elaborated by means of univariate and multivariate methods. It was interesting to notice that, in both datasets, the time-related information was not visible by simply comparing the profiles of signals, poorly visible in the principal component space, and clearly explained by three-way Principal Component Analysis (3-way PCA).