Dynamic testing rheology and fluorescence spectroscopy investigations of surface to centre differences in ripened soft cheeses

The viscoelastic properties and the matrix structures of three different retailed soft cheeses (M1, M2 and M3), for which the manufacturing process was varied, were studied from the surface to the centre of the cheese using dynamic rheology and front-face fluorescence spectroscopy. The storage modulus ( G ′) and the loss modulus ( G ″) values of the samples increased from the surface to the inner part of the cheeses, while strain and tan δ decreased. Protein tryptophan (excitation: 290 nm; emission: 305–400 nm) and vitamin A (emission: 410 nm; excitation: 250–350 nm) spectra were recorded at 20°C in samples cut from the surface to the centre. For each cheese, the data sets containing fluorescence spectra and rheology data were evaluated using multidimensional statistical methods. In addition, the three cheeses were well discriminated by their spectra by applying factorial discriminant analysis. From the tryptophan fluorescence data sets, 94% and 87.7% good classifications were observed for calibration and validation groups, respectively. A better classification (100% and 96% for principal and test samples) was obtained from the vitamin A spectra. Canonical correlation analysis was performed on the rheology and tryptophan fluorescence spectral data sets, and on the rheology and vitamin A fluorescence spectra data sets. The two groups of variables were found to be highly correlated since the squared canonical coefficients for canonical variates 1, 2, 3, 4 were higher than 0.98. These high correlations indicate that cheese rheology is a reflection of its structure at the molecular level.