Analysis of cocoa products for ochratoxin A and aflatoxins

摘要

Eighty-five samples of cocoa products sampled in Canada were analysed for ochratoxin A (OTA) and aflatoxins in 2011–2012. Inclusion of the aflatoxins in this survey required additional method development. Chocolate was extracted with methanol–water plus NaCl, while for cocoa two successive extractions with methanol and methanol–water were made. Extracts were cleaned on an AflaOchra immunoaffinity column (IAC). Determination was by reversed phase high performance liquid chromatography (HPLC). Detection of the aflatoxins was with a post-column photochemical reactor and of OTA by fluorescence detection. Mean limits of quantification (LOQ) of chocolate and cocoa powders were 0.16ng/g (OTA) and 0.07ng/g (aflatoxin B1), respectively. Survey results showed that the incidences of OTA above the LOQ in natural cocoa were 15/15 (mean 1.17ng/g), 20/21 for alkalized cocoa (mean 1.06ng/g), 9/9 for baking chocolate (mean 0.49ng/g), 20/20 for dark chocolate (mean 0.39ng/g), 7/10 for milk chocolate (mean 0.19ng/g), 5/5 for cocoa liquor (mean 0.43ng/g), and 0/5 for cocoa butter. These results confirm our previous work with OTA. In the same samples, incidences of aflatoxin B1 above the LOQ were 14/15 for natural cocoa (mean 0.86ng/g), 20/21 for alkalized cocoa (mean 0.37ng/g), 7/9 for baking chocolate (mean 0.22ng/g), 16/20 for dark chocolate (mean 0.19ng/g), 7/10 for milk chocolate (mean 0.09ng/g), 4/5 for cocoa liquor (mean 0.43ng/g), and 0/5 for cocoa butter. Both aflatoxins and OTA were confirmed by HPLC-MS/MS when OTA or aflatoxin levels found were above 2ng/g in cocoa.