Molecular authentication of surimi-based products (fish cakes, 鱼糕) sold on the Chinese e-commerce: Traditional (DNA barcoding) and innovative techniques (metabarcoding) to tackle seafood fraud

Surimi-based products (SBP), such as fish cakes, being processed products generally composed by mixture of species, are particularly susceptible to species substitution fraud. In this study, 56 fish cakes products (FCP) purchased on the Chinese e-commerce were analyzed using DNA barcoding (COI and cytb) to identify the dominant fish species and compare it to the fish trade name reported on the label. Part of them were also analyzed by metabarcoding (16S rRNA), also including positive and negative control samples, to better evaluate their composition. Overall, 12 different fish trade names were reported on the labels, of which only eight (42 FCP) attributable to a taxonomical ranking (species level or higher). In 61.9% of them (26 FCP), the fish trade name did not correspond to the species identified by DNA barcoding. Interestingly, the dominant species identified in some FCP using COI gene was pork (declared in the label) instead of a fish species. Potential fraudulent substitution cases were hypothesized. In the metabarcoding analysis, based on the control samples results, 0.2% was assumed as threshold value to filter the data and interpret the final results. In 71.1% of the cases the species identified by DNA barcoding corresponded to the main species identified by metabarcoding. However, from two to 11 different species per sample (average 5.8) were detected by metabarcoding, including undeclared cephalopods that can potentially represent a health risk for consumers. Metabarcoding was confirmed the best choice for the authentication of SBP, especially for detecting species used as minor ingredients. Outcomes from this study can be useful to implement more targeted management systems.