Authentication of apple juice categories based on multivariate analysis of the synchronous fluorescence spectra

Abstract

The usage of synchronous fluorescence as a means for discrimination between the commercial apple juice categories was studied. We recorded total synchronous fluorescence spectra (TSFS) of commercial apple juices belonging to the two categories: those produced directly - not from concentrate (NFC), and those reconstituted from concentrate (FC).An exploratory study of the spectra using the principal component analysis (PCA) revealed differentiation between the juices of the two categories based on their fluorescence.Partial least squares discriminant analysis (PLS-DA) was used for the development of the classification models. The analysis was performed for the unfolded TSFS (uTSFS) and individual synchronous fluorescence spectra (SFS) measured at particular emission-excitation wavelength offsets (Δλ), from 10 to 160 nm with 10 nm step. The best discrimination results were obtained for the model using uTSFS in the range of Δλ = 30–160 nm, with cross-validation and external validation error rates of 0.05 and 0.06, respectively. Models based on selected individual SFS also showed similarly good predictive ability, with cross-validation and external validation error rates of 0.08 and 0.05, respectively, for the SFS measured at Δλ = 70 and 90 nm. The analysis of significant variables using selectivity ratio (SR) suggests that the fluorescence of non-enzymatic browning products may significantly contribute to the differentiation of FC and NFC juices.