DNA Extraction from Olive Oil and PCR Amplification of Microsatellite Markers



ABSTRACT: DNA was extracted from single-cultivar of cold-pressed (virgin) unfiltered and cotton-filtered olive oils that were stored at 4 °C for up to a year using different DNA extraction kits and protocols. DNA was amplified using original and nested primers designed on 6 microsatellites loci of the UDO series. The most consistent results in terms of successful single sequence repeat amplifications were achieved using the Qiagen QIAamp DNA stool extraction kit, slightly modified and applied to oil sample amounts as small as 200 μL without any pretreatment. The kit allowed getting polymerase chain reaction (PCR) amplicons visible on gel and scorable peaks at the automatic sequencer for all 6 markers analyzed. Less consistent results were achieved with other kits, such as the Promega Wizard Magnetic DNA Purification System for Food, the LB Link-Biotech ExtMan 50–100 Evolution, the Qiagen Plant Mini kit, and the standard cetyltrimethyl-ammonium bromide-based DNA extraction protocol. The integration in the protocols of further tools, such as the hexane-based phase separation, the addition of water or NaCl solutions to the oil, the precipitation and the use of the pellet, and others, did not result in any substantial use. PCR amplifications that gave low DNA yields were improved by adopting the nested PCR technique, which uses the product of the 1st PCR as a template for a 2nd PCR carried out by means of internal primers. Conclusions are drawn as to the applicability of the method to trace the identity of single-cultivar virgin olive oils. Further work is required to check the sensitivity of the method in determining the varietal composition of blended oils, especially in detecting alleles from cultivars present in only small amounts.