Front face fluorescence spectroscopy coupled with chemometric tools for monitoring the oxidation of semi-hard cheeses throughout ripening

The purpose of this study was to assess the potential of the 400–640 nm emission fluorescence spectra after excitation set at 380 nm to monitor the changes in spectra and oxidation of 24 semi-hard cheeses, produced during autumn (n = 12) and summer (n = 12) periods, throughout ripening. Emission fluorescence spectra were recorded at the surface and at the inner layers of cheeses at 2, 30 and 60 days of ripening. The factorial discriminant analysis (FDA) applied on the first 5 principal components (PCs) of the principal component analysis (PCA) carried out on the 400–640 nm emission spectral data set recorded at the surface layers of cheeses produced during autumn or summer period showed a good discrimination of cheeses. Less good classification was obtained from cheese samples cut at the inner layers. In a second step, the 400–640 nm emission fluorescence spectra recorded at the surface or the inner layers of cheeses produced during autumn and summer periods were gathered into one matrix and analysed by FDA. Considering fluorescence spectra recorded at the inner layers, correct classification was observed for 67.4% and 62.3% for the calibration and cross-validation samples, respectively. Better classification was obtained for cheeses cut at the surface layers since 93.7% and 90.3% of the calibration and cross-validation samples respectively, were correctly classified. The obtained results showed that the 400–640 nm emission fluorescence spectra were primarily affected by light and oxygen then by the physico-chemical changes that occurred throughout ripening.