DETECTION OF TILAPIA DNA IN FISH PRODUCTS BY REAL-TIME PCR

A method has been developed for the detection and semi-quantitative assessment of tilapia content in fish products using polymerase chain reaction in real time in order to identify facts of substitution of more valuable and expensive fish species with tilapia. The method is based on the use of multiplex PCR to identify a fragment of the rhodopsin gene specific to tilapia genera Oreochromis, Sarotherodon and Coptodon with simultaneous amplification of internal endogenous control. A comparison of methods for DNA extraction from several types of fish products was carried out. It has been shown that precipitation and sorption extraction methods can be used to isolate DNA, and the express method can be used to isolate DNA from samples of single-component products (minced meat and fillet) in order to reduce the time spent on studying these samples. Examining a control panel of DNA samples from various fish species, the method showed 100 % specificity. The absolute sensitivity limit of the method for identifying tilapia genetic material was 200 copies/reaction. The detection limit of the method was 0.05 wt%. The method was approved by testing 83 samples of single-component and 28 samples of multi-component fish products selected from various retail outlets in Moscow and the Moscow region. Two samples contained tilapia DNA that was not declared in the product. The proportion of tilapia DNA detected was in the range of 0.1 % - 1 %, that may indicate accidental contamination during production. The existing requirements for the labeling of fish products are discussed in connection with the admissibility of such impurities. The proposed methodology can be used to monitor the correct labeling of fish.