Résumé
Chocolate quality is largely due to the presence of polyphenols, and especially of flavan-3-ols (condensed tannins and their derivatives) that are present in large amounts in cocoa beans and contribute bitterness and astringency to the final product.Prediction of chocolate quality from cocoa composition would be of great help for chocolate makers who currently base their sourcing on a time consuming and costly procedure involving sensory analysis of chocolates made using a standardized process. The aim of the present work was to investigate the potential of polyphenol-fingerprints for discrimination of cocoa samples and their attribution to chocolate sensory groups.Sixty cocoa samples have been processed into chocolates cocoa samples and attributed to four different sensory groups by sensory analysis. Cocoa polyphenol extracts have been prepared from the ground and defatted cocoa beans and analyzed by UHPLC-ESI-IT-MS. Averaging the mass spectrum recorded on the whole UHPLC profile provided cocoa polyphenol fingerprints, which were combined into a matrix and processed with chemometrics (PCA, PLS-DA) to select the most meaningful molecules for discrimination of the chocolate sensory groups.Sixteen samples representative of the four sensory groups were used for selection of the most discriminant variables. Non supervised PCA analysis of the average mass spectra showed that IT-MS is sensitive and quantitative enough to discriminate the sensory groups without prior selection of target compounds, i.e polyphenolic bio-markers. A supervised chemometrics treatment, PLS-DA, was applied to this data to select the most relevant molecules for the discrimination. A larger set of 44 cocoa samples was used to validate the results. The fingerprinting method proved to be quick and efficient and the chemometrics analysis highlighted 29 mass signals of known and unknown molecules that were finally targeted [1], enabling sensory-group discrimination. Most of these signals were attributed to flavan-3-ols, including 2 newly described ethyl-bridged flavan-3-ols [2].[1] Fayeulle et al., Fast Discrimination of Chocolate Quality Based On Average Mass Spectra Fingerprints of Cocoa Polyphenols, J Agric. Food Chem., 2019, 67, 2723-2731[2] Fayeulle et al., Characterization of new flavan-3-ol derivatives in fermented cocoa beans, Food Chem., 2018 (259), 207-212