Near infra-red characterization of changes in flavan-3-ol derivatives in cocoa (Theobroma cacao L.) as a function of fermentation temperature.

Flavan-3-ols were successfully extracted from cocoa by the Fast-Prep device and analyzed by HPLC-DAD, and their identifications were confirmed by injection of authentic standards. (-)-Epicatechin was the most abundant component with an average of 9.4 mg/g dried cocoa powder. More than 700 cocoa samples were used to calibrate the NIRS. An efficient calibration model was developed to accurately determine any flavan-3-ol compound of ground dried cocoa beans (SEP = 2.33 mg/g in the case of total flavan-3-ols). This performance enabled NIRS to be used as an efficient and easy-to-use tool for estimating the level of targeted compounds. The analysis of the PLS loadings of the model and pure epicatechin spectra gave proof that NIRS was calibrated on an indirect strong correlation resulting in the changes in flavan-3-ols during fermentation and their interaction with some major components, such as proteins. Total flavan-3-ol concentration fell from an average of 33.3 mg/g for unfermented samples to an average of 6.2 mg/g at the end of fermentation. Changes in flavan-3-ol content were dependent upon the origin and highly correlated to the fermentation level expressed as the sum of temperatures (average R(2) = 0.74), a good marker of the fermentation process and of the heterogeneity of the batch.