Prediction of the hydrophilic antioxidant capacity of tomato pastes from the IR and fluorescence excitation–emission spectra of extracts and intact samples

• Antioxidant, IR and fluorescence properties of tomato pastes were evaluated.
• PLS and N-PLS methods were used to model antioxidant properties.
• Figures of merit of models built using IR and fluorescence spectra are compared.

The performance of the recently proposed excitation–emission fluorescence method was compared to the method using infrared measurements for the evaluation of the antioxidant properties of intact samples and extracts that had been obtained from tomato pastes. The oxygen radical absorbance capacity assay (ORAC) was applied in order to estimate the antioxidant capacity of the extracts, while the Folin–Ciocalteu reagent was adopted for the evaluation of the total phenolic content. The optimal extraction conditions for tomato pastes (three minutes of sonication under 80 °C) were determined using the central composite design. Chemometric models such as the partial least squares regression and its N-way variant were further constructed in order to predict the antioxidant capacity or total phenolic content of the samples using either the IR or fluorescence spectra. The prediction errors that were obtained for the total antioxidant content were evaluated as the Trolox equivalents from the ORAC assay and were found to be equal to 2.011 (14.21%) for the fluorescence and 2.426 (17.15%) for the IR spectra, respectively. The prediction errors of the total phenolic content expressed as gallic acid equivalents were 0.067 (10.78%) for the fluorescence and 0.033 (5.36%) for the IR spectra, which were used as independent variables in the regression models.

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