ИСТИНА

Plants are the key components of many food products, in particular, teas, spices and herbal remedies. The inconsistency between declared and real composition, which often occurs in such products, can lead to serious health problems. A usual approach to quality control of food products that include plant components is the botanical analysis. It has however several limitations (not suited for highly processed products, lacks resolution for many plant taxa). Analysis based on the sequencing of genome regions that are variable at species level (DNA barcoding) seems to be the most promising approach successfully tested on honey and herbal supplements. To expand it on larger set of plant products we analyzed 6 teas, 6 spices and 6 herbal remedies available on Russian market. We tested three methods of DNA extraction to choose one that minimizes its degradation and the presence of PCR inhibitors. The composition of samples was determined by sequencing of nrITS1 sequences and their alignment on local nrITS reference database. For DNA library preparation optimized primers for nrITS1 were used that selectively amplify plants only and not fungi. For PCR we used two polymerases, one of which is high-fidelity and optimized for the amplification of GC-rich regions and other is less accurate but highly processive and resistant to PCR inhibitors. Sequencing was performed on two platforms - Illumina (MiSeq) and semiconductor sequencing (Ion S5). We found that most of the labeled plants were found in analyzed products, but three products had significantly different contents than declared by the manufacturer. Certain discrepancies in the results between the two HTS platforms were also found. In addition, we found that one of the tea blends contains inhibitors that can completely inhibit PCR with high-fidelity polymerase, even after additional DNA purification, but could be amplified with the robust one.