Monitoring free radical generation and antioxidant activity in tomato pulp using electron paramagnetic resonance (EPR): effects of ultrasound-assisted bioactive extraction

The effects of ultrasound-assisted processing on bioactive compounds, antioxidant activity, colour parameters, and free radical formation in tomato pulp were investigated. Treatments at different amplitudes and durations were applied to evaluate changes in bioactive compounds and oxidative processes. Ultrasonic processing showed a strong dependence of bioactive compound extraction, antioxidant activity, and radical formation on treatment parameters, with most conditions increasing total phenolic content (TPC) and antioxidant activity, while generally reducing carotenoid levels. TPC reached maximum of 0.380 mg/mL, while antioxidant activity ranged from 56.13% to 78.63% radical inhibition. Lycopene generally decreased under most conditions, with a maximum of 3.036 μg/mL observed under mild treatment, whereas beta-carotene showed minor variations, reaching up to 1.042 μg/mL. Colour parameters (a* and b*) were significantly affected by processing conditions and were closely associated with lycopene, while lightness (L*) remained stable. EPR spin trapping confirmed a balance between sonochemically produced reactive species and scavenging activity of antioxidant compounds released during processing. A complex interaction was observed between bioactive compounds and oxidative behavior: increased TPC contributed to higher antioxidant activity, while lycopene appeared to influence radical levels. Ultrasound processing improved the functional properties of tomato pulp, highlighting ultrasound technology for controlled modification of food quality and oxidative processes, although further optimization is needed.