High intensity ultrasound as a physical elicitor affects secondary metabolites and antioxidant capacity of tomato fruits

The aim of this study was to evaluate the effect of ultrasound on secondary metabolites and antioxidant capacity of commercially mature tomato fruits. Ultrasound treatment (25 kHz, acoustic power density of 26 W/L) was applied to tomatoes submerged in a treatment tank filled with water for 1–4 min. Afterwards, the tomatoes were stored at room temperature for up to 48 h. Selected secondary metabolites, antioxidant capacity (1,1-diphenyl-2-picryl-hydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS)), and phenylalanine ammonia-lyase (PAL) activity of the ultrasound-treated tomatoes were analyzed at 2 h, 24 h, and 48 h. The ultrasound treatment increased the accumulation of secondary metabolites, including total phenolic, lycopene, carotenoids and ascorbic acid during storage. After a 48-h storage, the DPPH and ABTS antioxidant activity of the tomatoes treated with ultrasound for 2 min increased 22.69% and 11.55% compared with the control, respectively. The PAL activity of the ultrasound-treated tomatoes (2 min) was 16.25% higher than the control after storage for 48 h. These results indicate that ultrasound treatment could enhance the beneficial health effect of tomatoes. The enhancement could be attributed to the eliciting effect of ultrasound, which may have regulated the metabolic responses of the tomato fruits.