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Hydroperoxides are primary lipid oxidation products that can provide an early and accurate indication of the oxidative status of food products before sensory characteristics are affected. However, its analytical determination is challenging (Bou et al., 2008). The aim of this study was to evaluate the ability of near infrared spectrometry (NIRS) to determine the total hydroperoxide content in fish as a tool to rapidly estimate its susceptibility to oxidation.
To do so, hydroperoxides were enzymatically produced using lipoxidase from Glycine max (Merck KGaA, Germany) on emulsified linoleic acid to obtain a hydroperoxide stock solution (327µM), which was diluted in a control emulsion without enzyme to obtain 82 samples with concentrations ranging between 0 and 327 µM. Next, these emulsion systems containing hydroperoxides were combined with a fresh fish matrix (fish:emulsion, 1:2.25, w/v), obtaining fish-based samples with concentrations from 33 to 256 µM. Spectra were acquired using a high-performance Fourier Transform NIR spectrometer (Bruker Optik, Germany). Partial least squares regression was used to develop predictive models (PLS Toolbox, The MathWorks Inc., USA). PLS loadings were analysed to identify the most relevant wavelengths for the prediction of hydroperoxide content.
First derivative of raw spectra resulted in satisfactory predictions of hydroperoxide content in both emulsion (R2=0.88; RMSEP=39.7 µM) and fish matrix (R2=0.84; RMSEP=28.0 µM) samples. The first PLS loading for the emulsion model showed three relevant regions at around 8770, 7560 and 7270 cm-1. For the fish-based model, similar regions were observed (8770, 7520 and 7200 cm-1) and spectral range between 4500 and 6500 cm-1, related to decomposition products such as aldehydes and alcohols, was not included since it could interfere in the prediction.
In conclusion, the obtention of a rapid procedure based on NIRS for evaluation of oxidation susceptibility and shelf life in fish seems feasible. However, more experimental work is needed.
