Explorative spectrometric evaluations of frying oil deterioration

The potential of spectroscopy as a reliable and fast method for determining the deterioration of frying oils was investigated. Daily oil samples were collected from a commercial Chinese spring roll plant. The plant was operated one shift, 5 d a week, then cleaned and restarted with fresh oil every 4 wk. Each oil sample was analyzed by 11 chemical/physical methods and fluorescence, near infrared/visible (NIR/VIS), Fourier transform infrared (FT-IR) and FT-Raman spectroscopic procedures. The results were evaluated and compared by principal-component analysis and partial least squares regression. Most chemical/physical and all spectroscopic methods detected the deterioration during the first half of the frying cycle. Thereafter, an equilibrium occurred between deterioration processes and replenishment with new oil. At equilibrium, the correlation between frying time and the various methods was nonlinear. FT-IR with the attenuated total reflectance sampling technique was the most direct and accurate method of monitoring gross changes in the frying oil. Fluorescence was the technique that provided the best models for anisidine value, oligomers, iodine value, and vitamin E. NIR/VIS spectroscopy proved to be a good general-purpose technique. The study demonstrated that spectroscopic sensors have the potential to replace titration and chromatographic procedures, and can be used in combination with chemometric data analysis to optimize deep-frying operations.