Elemental Chemometrics as Tools to Depict Stalked Barnacle (Pollicipes pollicipes) Harvest Locations and Food Safety

Abstract

The stalked barnacle Pollicipes pollicipes is an abundant species on the very exposed rocky shore habitats of the Spanish and Portuguese coasts, constituting also an important economical resource, as a seafood item with high commercial value. Twenty-four elements were measured by untargeted total reflection X-ray fluorescence spectroscopy (TXRF) in the edible peduncle of stalked barnacles sampled in six sites along the Portuguese western coast, comprising a total of 90 individuals. The elemental profile of 90 individuals originated from several geographical sites (N = 15 per site), were analysed using several chemometric multivariate approaches (variable in importance partial least square discriminant analysis (VIP-PLS-DA), stepwise linear discriminant analysis (S-LDA), linear discriminant analysis (LDA), random forests (RF) and canonical analysis of principal components (CAP)), to evaluate the ability of each approach to trace the geographical origin of the animals collected. As a suspension feeder, this species introduces a high degree of background noise, leading to a comparatively lower classification of the chemometric approaches based on the complete elemental profile of the peduncle (canonical analysis of principal components and linear discriminant analysis). The application of variable selection approaches such as the VIP-PLS-DA and S-LDA significantly increased the classification accuracy (77.8% and 84.4%, respectively) of the samples according to their harvesting area, while reducing the number of elements needed for this classification, and thus the background noise. Moreover, the selected elements are similar to those selected by other random and non-random approaches, reinforcing the reliability of this selection. This untargeted analytical procedure also allowed to depict the degree of risk, in terms of human consumption of these animals, highlighting the geographical areas where these delicacies presented lower values for critical elements compared to the standard thresholds for human consumption.

Harnessing the Full Power of Chemometric-Based Analysis of Total Reflection X-ray Fluorescence Spectral Data to Boost the Identification of Seafood Provenance and Fishing Areas

“…Observing the higher data point density regions, it is possible to distinguish four main peaks with a particularly high density of VIP scores with noticeable high values (VIP > 1.5–2). The first observable peak area corresponds to the beginning of the spectra, where it corresponds to low-atomic-number (Z) elements such as Na, K, and Ca, highly abundant in marine species [ 12 , 13 , 14 , 42 , 43 ]. The last three observable peaks correspond to an area where Cu, Zn, Br, Sr, Pb, and other high-Z elements, have one of the main fluorescence peaks, with these elements also being very abundant in marine seafood samples [ 12 , 13 , 14 , 42 , 43 ].…”

“…The first observable peak area corresponds to the beginning of the spectra, where it corresponds to low-atomic-number (Z) elements such as Na, K, and Ca, highly abundant in marine species [ 12 , 13 , 14 , 42 , 43 ]. The last three observable peaks correspond to an area where Cu, Zn, Br, Sr, Pb, and other high-Z elements, have one of the main fluorescence peaks, with these elements also being very abundant in marine seafood samples [ 12 , 13 , 14 , 42 , 43 ]. Nevertheless, the use of specific elements instead of the full TXRF spectra greatly reduces the number of features used as input for the chemometric approaches, from several thousand to a few dozen, as it is observable between elemental analysis and other spectral fingerprinting approaches [ 40 , 43 ].…”

“…Several techniques have been employed to trace the geographical origin of food products, including elemental analysis [ 9 , 10 , 11 , 12 , 13 , 14 ], isotope analysis [ 15 , 16 , 17 ], fatty acid profiles [ 18 , 19 , 20 ], and optical spectroscopy techniques [ 21 , 22 , 23 ]. These techniques, alone or combined, produce large datasets that can be analyzed either through classical statistical techniques or by advanced chemometric approaches [ 14 , 21 , 22 , 24 , 25 ].…”

“…Total reflection X-ray fluorescence (TXRF) spectroscopy elemental data have a high degree of accuracy in depicting elemental signatures of seafood products of different geographical origins [ 12 , 13 , 14 ]. Nevertheless, as with other spectroscopy techniques, the generated spectra contain more information than the one used to calculate specific indexes or compound concentrations [ 21 , 23 , 26 , 28 ].…”

Combination of Total-Reflection X-Ray Fluorescence Method and Chemometric Techniques for Provenance Study of Archaeological Ceramics

“…Recently, studies have explored the combination of TXRF with chemometric methods as a possible tool for the analysis of complex samples. This combination was already successfully applied in the discovery of obesity markers [ 29 ], identification of the geographical origin of bean seeds [ 30 ], classification of the origin and type of wine samples [ 31 ], discrimination of gunshot residues [ 32 ], and seafood provenance assessment [ 33 , 34 ]. This approach was also applied to the analysis of archaeological ceramics [ 35 ], but the data in this work were investigated using principal component analysis (PCA), which is an exploratory method and does not allow the classification of samples.…”