Balanced nutrition is essential for optimal health. Fish is a very healthy food containing vital proteins, fats, and vitamins necessary for good nutrition, health, and immunity 1. Moreover, it is more available and relatively inexpensive than the other animal protein sources in various countries2. However, the fishery products' regional price, especially fish fillets, varies according to the type and availability of the utilized fish. As a result, the fish fillet is exposed to massive modifications in its shape and appearance, increasing the probability of mislabeling or substitution with the aim of cheating for illegal economic gains3,4. Tilapia (Oreochromis niloticus) and Nile Perch (Lates niloticus) are the most common fish fillet types in the Egyptian market 5,6. However, due to the vast production of Tilapia in Egypt with limited exportation to the external markets 7, its price is almost half that of the Nile Perch fillet 8. Consequently, substituting such high-priced fish types with the cheaper ones mostly when sold as fish fillet is sometimes common. Therefore, it is essential to disclose the substitution and mislabeling, mostly deliberate, which is an actual adulteration, in the species used in fish fillet production.
Genetic and immunological assays methods 9–13 have been used for fish substitution detection. However, these destructive methods are costly, time-consuming, and require special laboratories with many samples. On the other hand, multimode hyperspectral imaging14 and spectroscopic techniques have been widely used in pharmacology15, biology 16, and the food industry to inspect the quality and substitution probability of their products17,18.
Laser-Induced Breakdown Spectroscopy (LIBS) is a well-known spectrochemical elemental analysis technique that has been utilized in many biological applications since more than twenty years ago. In this technique, Q-switched nanosecond laser pulses are focused onto the sample surface, inducing a plasma plume that consists of a collection of ions and swirling electrons at enormously elevated temperatures (> 6000 K). In cooling down the plasma plume, it gets rid of the previously absorbed laser energy by emission photons at different wavelengths. The emitted light is collected by a suitable optical system and fed to the entrance slit of a spectrometer equipped with a light detector (mostly ICCD) for dispersion and detection of the light spectrum.
The obtained emission spectrum includes the characteristic spectral lines of the elements present in the plasma plume and, thus, in the sample material in the case of stoichiometric ablation, considering the self-absorption and the matrix effect. The LIBS technique is detailed experimentally and theoretically in many books and review papers19–21
Laser-induced breakdown spectroscopy (LIBS) is characterized by being a simple, fast, and non-destructive method; besides, it can be used in situ via the nowadays commercially available portable or mobile LIBS systems. LIBS has already been utilized to detect adulteration in milk22, beef 23, and butter 24, in addition to investigating meat substitution25 and red wine classification 26. Furthermore, LIBS data has been statistically analyzed using chemometric techniques such as partial least squares, artificial neural networks, and principal component analysis 27–30. Recently, neural networks, as a supervised technique, have been considered efficient classifiers for many non-linear problems. Therefore, it has been significantly utilized to evaluate the classification rate LIBS data31.
In the present work, laser-induced breakdown spectroscopy has been employed to discriminate between samples of commercial Tilapia and Nile Perch fillets. Moreover, LIBS has also been used to test the difference in tenderness between the two types of fish fillets. The spectroscopic data has been validated via conventional analysis of the investigated fish fillet samples. In addition, the chemometric PCA and ANN methods were exploited to analyze the obtained spectroscopic results statistically.