Written in ink: Elemental signatures in octopus ink successfully trace geographical origin

Abstract

In recent years, validation of seafood authenticity and provenance has attracted the attention of authorities and consumers. Increasing levels of food fraud has raised awareness regarding seafood traceability, especially in highly valuable and highly consumed seafood products, such as the common octopus (Octopus vulgaris). Seafood traceability studies based on trace element fingerprinting generally focus on muscle tissues or carbonate structures whilst the ink fluid has been overlooked. Untargeted multi-element Total Reflection X-ray Fluorescence (TXRF) analysis of O. vulgaris ink successfully discriminated four collection areas [91.2 % and 84.1 % using Variable Importance in Projection Partial Least-Squares Discriminant Analysis (VIP-PLS-DA) and Linear Discriminant Analysis (LDA), respectively] along the mainland Portuguese coast (ca. 900 km coast in the Northeast Atlantic). Arsenic, Pb, Na, Sr and Rb were highlighted as elements with higher contributions for sample discrimination between the four considered capture areas. Regarding food safety, it is important to note that some ink samples Cu, Mn and Pb concentrations exceeded human consumption recommended values. Thus, the results show that untargeted TXRF spectroscopy analysis of O. vulgaris ink is a reliable tool for disentangling the geographical origin of the octopus, as well as to inform about the food safety of octopus ink.