Soy detection in canned tuna by PCR and capillary electrophoresis

Abstract

Tuna is a commercially important fish species that accounts for a significant proportion of the global fish market. The annual canned tuna consumption in Mexico is approximately 1.6 kg per capita. Consequently, tuna is more than likely to be fraudulently substituted with lower-priced fish species or mixed with soy products. Recently, interest has been focused on DNA analysis instead of protein-based assays. DNA is more thermo-stable than protein and can be used to analyze processed products such as canned fish. Polymerase chain reaction (PCR)-based methods are frequently used for soy detection in different heat-processed foods. Usually, amplified DNA fragments are separated by conventional electrophoretic methods. The present study aimed to develop a capillary gel electrophoresis (CGE) method, using laser-induced fluorescence (LIF), to detect soy DNA in canned tuna. The conditions for DNA extraction and PCR were optimized. DNA extraction was carried out using the GENCLEAN® commercial kit protocol with modifications. The PCR products of the constituent gene Le1 (118 bp) were analyzed for the detection of soy. For the detection of Thunnus albacares, the 350 bp from Cytb gene fragment was used. Results showed that DNA extraction was accurate for different soy percentages since concentration ranged from 1 to 70 ng μL⁻¹ (R² = 0.99). Moreover, the selected primer for either tuna or soy was shown to be specific by gel electrophoresis, while some band smearing was seen for canned tuna. On the other hand, the characteristic tuna fragment (350 bp) and soy fragment (118 bp) were unequivocally identified by CGE using the Low DNA mass ladder and ΦX174 RF DNA/Hae III standards, respectively. Thus, the PCR-CGE method presented is a suitable technique for the semi-quantitative detection of soy in canned tuna. However, further studies are required in order to quantify soy in canned tuna by using quantitative competitive PCR followed by CGE.