engleski

Electrochemical determination of carotenoids in fish samples

High quality aquaculture products must fulfil several requirements, including the adequate color and nutritional value. As fish cannot synthesize pigments, the coloring agents need to be incorporated into their diet. The most used coloring agents are carotenoids. Carotenoids are a diverse class of polyisoprenoid hydrocarbons (carotenes) and their oxygenated derivatives (xanthophylls) and have an important role as defenders from UV-Vis light, precursors of vitamin A and natural antioxidants. Due to the positive effects on health, various methods that would allow their easy and quick determination are researched. Until now, electrochemical investigations of carotenoids have been performed in non-aqueous media [1] with an exception of some studies in micelle systems [2] and as self-assembled monolayers (SAM) in aqueous phase [3]. Voltammetric measurements for characterization of carotenoids in fish samples are also sparse in literature, so this approach could provide a better knowledge of their mechanism of action and input into their use in aquaculture and potentially beneficial effects on human health when consuming fish food. In this study, relatively new voltammetric method for the characterization of carotenoids (astaxanthin, lutein and β-carotene) and their detection in fish samples named stripping voltammetry microprobe (SPV) [4] was applied. This method is based on a formation of a precipitate film of analyte on the electrode surface by pipetting 5 μL of analyte dissolved in organic solvent and allowing the solvent to evaporate in air. By means of this technique, lipophilic compounds could be analyzed in aqueous media. Measurements were conducted on a paraffin impregnated graphite electrode (PIGE) using square-wave voltammetry (SWV) in a wide range of potential scan rates in 0.1 M HClO4 aqueous electrolyte. Prior to the analysis, fish samples were macerated in acetone allowing the extraction of carotenoids present in samples. The results revealed that the oxidation of different carotenoid standards is not similar. While β-carotene and lutein showed one irreversible peak at E = 0.453 V and E = 0.687 V, respectively, oxidation of astaxanthin turned out to be more complex process. It has one well defined reversible peak at E = -0.350 V followed by one poorly defined shoulder at E = -0.109 V and smaller reversible peak at E = 0.470 V. Analysis of fish samples precipitates on the surface of PIGE was performed using SWV under optimal experimental condition: ESW = 50 mV, f = 100 Hz, dE = 2 mV. Both salmon and bass samples revealed a reversible peak at the same potential, E = 0.960 V. Proposed method showed good sensitivity and applicability on real samples and has a potential of further development.

Carotenoids ; fish ; voltammetry ; aqueous media

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