Multiway fusion of NIR and EEM data for the determination of synthetic caramel in Balsamic Vinegar of Modena

Synthetic caramel is among the most widely used colourants in the food industry. The use of caramel in Balsamic Vinegar of Modena PGI is regulated by the protocol of the Consortium of Balsamic Vinegar of Modena [1]. The addition of caramel may be allowed for colour stabilization and must be declared on the product label. Among the various colouring agents, the most commonly used is the Class IV additive, E-150d, also known as sulphite ammonia caramel. However, caramel may also be “naturally” present in balsamic vinegar due to cooked must, used as raw material during vinegar production. Currently, no official analytical method exists to distinguish between sulphite ammonia caramel and “naturally” occurring caramel in Balsamic Vinegars of Modena PGI. To address this, an analytical approach, combining two spectroscopic techniques, Near Infrared Spectroscopy (NIR) and Fluorescence Spectroscopy was employed. Vinegar samples were analysed both in their original state and after the addition of synthetic caramel. NIR spectra were acquired, pretreated in order to minimize the non-relevant information and submitted to explorative analysis by Principal Component Analysis. Fluorescence spectroscopy generated three-dimensional Excitation-Emission Matrices (EEMs) (i.e., samples × emission wavelengths × excitation wavelengths), which required a proper data analysis. Specifically, Parallel Factor Analysis (PARAFAC) [2] was applied to resolve and quantify fluorophores associated with caramel. NIR and EEM data will be fused at both low and mid-level, to build a model to determine the presence of synthetic caramel in balsamic vinegar samples from Modena.