Optimization of microwave-assisted extraction of hydrophilic and lipophilic antioxidants from a surplus tomato crop by response surface methodology

•Optimal MAE conditions for hydrophilic and lipophilic antioxidants were determined.•Time, temperature, ethanol concentration and solid/liquid ratio were relevant variables.•Concentration-time response methods (crocin and β-carotene bleaching) were applied.•The antioxidant capacity of the hydrophilic fraction was higher than the lipophilic one.•No significant difference between predicted and experimental values was found.

Tomato is the second most important vegetable crop worldwide and a rich source of industrially interesting antioxidants. Hence, the microwave-assisted extraction of hydrophilic (H) and lipophilic (L) antioxidants from a surplus tomato crop was optimized using response surface methodology. The relevant independent variables were temperature (T), extraction time (t), ethanol concentration (Et) and solid/liquid ratio (S/L). The concentration-time response methods of crocin and β-carotene bleaching were applied, since they are suitable in vitro assays to evaluate the antioxidant activity of H and L matrices, respectively. The optimum operating conditions that maximized the extraction were as follows: t, 2.25 min; T, 149.2 °C; Et, 99.1%; and S/L, 45.0 g/L for H antioxidants; and t, 15.4 min; T, 60.0 °C; Et, 33.0%; and S/L, 15.0 g/L for L antioxidants. This industrial approach indicated that surplus tomatoes possess a high content of antioxidants, offering an alternative source for obtaining natural value-added compounds. Additionally, by testing the relationship between the polarity of the extraction solvent and the antioxidant activity of the extracts in H and L media (polarity–activity relationship), useful information for the study of complex natural extracts containing components with variable degrees of polarity was obtained.

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