High Intensity Ultrasound as an Abiotic Elicitor—Effects on Antioxidant Capacity and Overall Quality of Romaine Lettuce

Abstract

The effect of ultrasound treatment at low acoustic power density (APD) on antioxidant capacity and overall quality of Romaine lettuce was evaluated. Whole leaf lettuce was treated with ultrasound (25 kHz) at APD of 26 W/L for 1–3 min and stored at room temperature for up to 150 h. Quality indices examined included color, texture, total phenolics, antioxidant capacity, and sensory properties. Phenylalanine ammonia-lyase (PAL) activity of lettuce from different treatments was monitored during storage. There were no differences in sample quality attributes between ultrasound treatment and control immediately after treatment. Lettuce treated with ultrasound exhibited an increase in PAL activity after storage for 60 h, resulting in production of phenolic compounds as secondary metabolites and enhancement of antioxidant capacity. Ultrasound-treated samples did not exhibit deterioration during storage, and under certain conditions, it delayed enzymatic browning and maintained better overall quality. A hypothetical model for the effect of low APD ultrasound as an abiotic elicitor on fresh produce was proposed based on the finding of present study and evidence from previous reports on response of cell cultures to ultrasond treatment.