The use of discriminant analysis for the interpretation of the reflectance spectra of irradiated porcine M-longissimus dorsi

Slices of porcine M. longissimus dorsi were packed in overwrap packs and subjected to irradiation (0 and 5 kGy) and then stored for 7 days at 4 degrees C. Reflectance spectra were measured on the outside surface and a freshly cut surface at 7 days post irradiation. The reflectance spectra were transformed to reflex attenuance, k/s and first and second difference spectra and subjected to discriminant analysis. Using discriminant analysis it was possible to establish a calibration equation to discriminate between the spectra of irradiated and unirradiated pork for both the outside and the inside surface. When the calibration model was used to predict the classification of new samples a 100% correct grouping was obtained for the freshly cut surface, however, for the outside surface the classification ranged from 87 to 100% correct depending on the mathematical transformation of the reflectance spectra. This shows the potential of colour measurements as a possible rapid initial screening test for the identification of irradiated pork. Evaluation of the first difference spectra to identify peak positions showed significant differences in peak positions between irradiated and unirradiated pork. The position of the peaks in the irradiated sample is discussed as lending support to the hypothesis of the carboxyhaem form as the irradiated pigment. (C) 2000 Elsevier Science Ltd. All rights reserved.