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Cocoa powder is a widely used food and ingredient, and is vulnerable to adulteration by cheaper ingredients.  A non-targeted metabolomics approach based on the use of reversed-phase liquid chromatography coupled to a high-resolution mass spectrometer (HPLC-HRMS) was developed to carry out the characterisation of cocoa powder samples adulterated at two different levels, with carob flour, soya flour, and chicory. The extraction procedure and chromatographic parameters were optimised to obtain the highest number of molecular markers. After chemometric analysis of the data, 21 and 37 metabolites in positive and negative ionisation modes, respectively, were found as potential authenticity and adulteration markers in the cocoa powder samples and simulated samples of adulterated cocoa powder. Of these, the identity of only 16 compounds in negative mode and 4 in positive mode could be determined, and most of these compounds belong to the groups of flavonoids, fatty acids, terpenoids, and lysophospholipids, which were potential markers for cocoa adulteration.

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Small amounts of low cost carob flour do not change the colour, aroma or taste characteristics of cocoa powder. Therefore, Spanish researchers have developed a NIR (near infra-red) method combined with chemometrics to determine that adulteration with carob flour has  taken place, and the amount of carob flour that has been used. Data sets using cocoa powders with different alkalisation levels, carob flours with three different roasting degrees, and adulterated samples prepared by blending cocoa powders with carob flour at several proportions, were obtained. For qualitative results, a principal component analysis (PCA) and a partial least squares discriminant analysis (PLS-DA) were used, giving a 100% classification accuracy to distinguish pure cocoa powders from adulterated samples. For quantitative analysis, a partial least squares (PLS) regression analysis was performed giving a root mean square error of prediction of 3.2%, thus making the method fit for purpose for determining the amount of carob flour in cocoa powder within this error.

              Read the abstract at: cocoa powder adulteration with carob flour