Oxidative changes in pork scratchings, peanuts, oatmeal and muesli viewed by fluorescence, near-infrared and infrared spectroscopy

The possibility of using rapid spectroscopic methods to detect lipid oxidation of four standard food products-peanuts, pork scratchings, oatmeal and muesli-were investigated in a large screening experiment. Fluorescence, near-infrared [including visual (Vis/NIR)] and infrared (IR) spectra have been recorded during and beyond the normal shelf lives of the products and related by means of multivariate data analysis to reference oxidation measures of free radicals and hexanal, as well as to sensory evaluation. For pork scratchings, the three spectroscopic techniques were able to monitor the progressing level of oxidation: IR with good correlation to hexanal (r(2)=0.86), Vis/NIR with good correlations to free radicals (r(2)=0.82) and fluorescence with good correlations to both free radicals (r(2)=0.76) and hexanal (r(2)=0.83). In the case of IR, the best result was obtained using the region including the out-of-plane C-H of trans-fatty acids. For the other three products, the results were generally inferior except for good correlations between fluorescence spectra and free radicals in peanuts (r(2)=0.73) and between Vis/NIR spectra and hexanal for muesli products (r(2)=0.8).