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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