RESUMO
The purpose of this work was to understand low recoveries of thiamine (vitamin B1) when extracted from cocoa-containing beverage powders fortified with water-soluble vitamin B1, and to develop and validate a new procedure to improve these results. Based on the literature, previous trials have focused on two main factors: pH value prior to paper filtration and the need for solid-phase extraction (SPE) clean up. We demonstrate that by following European Standard EN 14122, recovery of thiamine in cocoa-containing beverage powders is low and dependent on the test portion (86 and 72% for 0.5 and 1.5 g test portions, respectively). Our improved method resolved this problem by keeping the pH low (around 1) prior to paper filtration, leading to a 96.3% recovery and high precision (RSDr of 3.5%). The use of strong cation-exchange SPE cartridges for cleanup prior to the thiamine oxidation reaction proved to be essential. A comparison between our improved method and EN 14122 on nine cocoa-containing beverage samples available on local market from different manufacturers showed a systematic increase in thiamine content (up to 70%) when the improved method was applied. The highest difference was observed for the sample that contained the highest amount of cocoa. However, for beverage powders that contained both cocoa and milk, no difference was observed.