Changes in methylxanthines and flavanols during cocoa powder processing and their quantification by near-infrared spectroscopy

Variation in methylxanthines (theobromine and caffeine) and flavanols (catechin and epicatechin) was studied in a large set of cocoa powders (covering different origins, processing parameters and alkalisation levels). The content of these compounds was established by high-performance liquid chromatography (HPLC), whose results showed that the alkalisation process lowered the content of all analytes, whose loss was more evident in flavanols. Therefore, the determination of these analytes in a huge set of samples allowed not only better knowledge of the concentration variability in natural commercial cocoas from different origins, but also the understanding of the effect that industrial alkalisation has on these contents. The feasibility of reflectance near-infrared spectroscopy (NIRS) combined with partial least square (PLS) to non-destructively predict these contents, was also evaluated. All the analytes were generally well predicted, with predictions for methylxanthines (R-P(Z) 0.819-0.813 and RMSEP 0.068-0.022%, and bias 0.005 and 0.007 for theobromine and caffeine, respectively) and for flavanols (R-P(Z) 0.830-0.824; RMSEP 8.160-7.430% and bias - 1.440 and -1.034 for catechin and epicatechin, respectively). Thus NIRS could be an alternative fast reliable method for the routine assessment of these analytes in the cocoa industry.