3. Results and discussion
DNA was extracted from thirteen St. John's Wort products
on sale as over-the-counter herbal medicines or food supplements.
An initial test was carried out to amplify the 850 bp
Internal Transcribed Spacer (ITS) of the ribosomal RNA genes.
Just four of the samples yielded genomic DNA of sufficient
quality to amplify the entire region (Table 1), representing 30%
of the sample set. This is an expected result, as the processing
and manufacturing methods used to create these products can
be damaging to DNA. Under these conditions DNA can become
degraded and fragmented, resulting in broken strands of DNA.
If one of these breakages occurs in between the annealing
positions of PCR primers then an amplicon will not be formed
and the reaction will fail. The likelihood of a breakage between
primer annealing positions is positively correlated to the length
of the amplicon. Therefore it is important to carefully consider