Detection of residual free radicals in tomato juice processed by stand-alone and combined ultrasonic and ultraviolet treatments

This study investigated the effects of ultraviolet-A (UV-A), ultrasound (US), and combined UV–A/US treatments on bioactive compounds, antioxidant activity, and free radical generation in tomato pulp. Individual bioactive compounds responded differently to UV-A, US, and combined UV–A/US treatments, depending on treatment conditions and number of cycles. The highest total polyphenol content (TPC) was obtained under UV-A irradiation at 50 mW in the third treatment cycle (224.71 mg/L GAE), while lycopene and beta-carotene reached their maximum concentrations under UV-A at 100 mW (1.287 µg/mL and 0.286 µg/mL, respectively). The highest reduction of the EPR–DPPH signal was observed under combined UV–A/US treatment (31.49 %), whereas the US treated sample (60 % of amplitude) showed the lowest reduction (15.12 %). CMH spin trapping measurements showed that CP equivalents increased with treatment intensity and number of cycles, with the highest CP value (73.72 µmol/L) obtained under ultrasound treatment at 90 % amplitude after three cycles. UV-A treatment alone resulted in lower CP values, which increased gradually with higher irradiation power and additional cycles.