What's in your tea?

Herbal infusions, commonly referred to as herbal teas, are among the most widely consumed hot beverages. The popularity of herbal teas is mainly due to their claimed health-related properties and consumers’ preference for their specific taste and aroma. Herbal teas are sold in the market mainly as tea bags and ground or fragmented loose products. Because it is difficult to identify the botanical origin of a ground or processed product by its appearance, herbal products such as teas, spices, and dietary supplements are vulnerable to accidental contamination, deliberate substitution, or admixing with a less commercially valuable herbal species and undeclared fillers.

Researchers from turkey now developed a DNA assay to authenticate the botanical origin of herbal teas. They tested the efficiency of a PCR-capillary electrophoresis (PCR-CE) approach on commercial herbal tea samples using two noncoding plastid markers, the trnL intron and the intergenic spacer between trnL and trnF. The authors call these markers DNA Barcodes which is incorrect as none of them is a community-wide accepted DNA region. Nevertheless, it is not the first time trnL was used in a study related to DNA-based species identification and the results are quite promising. 

Single ingredient teas and different admixtures of pairs of herbal species were tested (linden/peppermint; sage/anise; rose hip/chamomile; sage/linden) and the researchers were able to identify deviations from standards (listed ingredients) which were further investigated by isolation of the alien fragments for sequencing. In one case a chamomile tea sample clearly contained other non-listed ingredients and a search in public databases revealed that it contained rosemary and was mislabeled as a single-ingredient product.

It is important to note that the utility of the PCR-CE barcode assays proposed in this work is not limited to herbal teas but can be extended to authenticate all types of processed herbal products or raw material. When an appropriate genomic region with sufficient interspecific size variation is selected as the analyte, capillary electrophoresis analysis is a faster, more cost-efficient, less equipment and labor/expertise demanding, and relatively simple alternative to sequencing for herbal product authenticity analyses. PCR-CE assays can be standardized for individual products by employing references based on the ingredients list and applied as routine tests for the verification of botanical origin. PCR-CE assays can also be coupled with sequencing any time adulteration is suspected in a sample.