Molecular identification of dried squid products sold in China using DNA barcoding and SYBR green real time PCR

Dried squid products are popular in China as a snack food, side dishes, or refreshments, and the market appeal can be reflected by the high price that occasionally reaches 497 RMB per kg. However, the absence of harmonisation around the definition of squid, as well as the problems with visual inspection for processed seafood products, make alternative species substitution for dried squid products a frequent occurrence. The aim of the present study was to apply a DNA barcoding approach for species identification of 48 dried squid products collected from the largest online shopping platform in China. Moreover, we also developed a novel SYBR green real-time PCR assay (simplex and duplex followed by a melting curve analysis) specific for Illex argentinus and Todarodes pacificus based on cytochrome C oxidase subunit I (COI) gene. Results highlighted the successful DNA extraction and PCR amplification of a 655 bp COI gene fragment from all products. A maximum similarity value in the range of 98-100% was obtained for all readable sequences using the BOLD and BLAST public databases and four species (Dosidicus gigas, Uroteuthis edulis, I. argentinus, and T. pacificus) were identified. The specificity of the designed primer sets was confirmed against 23 non-target species, and the newly developed methods were successfully applied to screen I. argentinus and T. pacificus in dried squid products. Overall, DNA barcoding is a robust tool for seafood species identification and the novel method is effective in screening I. argentinus and T. pacificus in food products.