Evaluation of the thermal stability and transfer rate of pyrrolizidine alkaloids during the brewing of herbal infusions contaminated with Echium vulgare and Senecio vulgaris weeds

Abstract

Pyrrolizidine alkaloids (PAs) are currently in the spotlight of food safety due to the potential health risk that their intake may entail for consumers. Among the wide variety of food products likely to be contaminated with PAs, teas and herbal teas stand out because of their cross-contamination with weeds from PA-producing plants. Accordingly, this work simulates the cross-contamination of chamomile tea samples with weeds of Senecio vulgaris and Echium vulgare to evaluate the effect of brewing on the PA content at different temperature (100 and 75 °C) and time (5 and 10 min) conditions. The results of the thermal degradation study revealed PAs are quite stable compounds under the conditions assayed, being the initial PA concentration the variable that strongly affected the thermal stability of these compounds, rather than the brewing temperature and time. On the other hand, it was confirmed that not all PAs are effectively transferred from the dry material to the infusion during the brewing process, leading to overall transfer rates between 13 ± 1 to 87 ± 10%. Also, it was observed that the extraction efficiency may be influenced by the type of matrix, since transfer rates were lower when the PA migration came from Echium vulgare than from Senecio vulgaris. Moreover, it was confirmed that the real content of PAs in a cup of tea can be overestimated in 2–7 times if their transfer rate is not considered during the brewing process, highlighting the importance of analyzing the infusion samples instead of the dry tea samples to correctly assess the risk exposure of consumers to these contaminants.