Effect of power ultrasound on quality of fresh-cut lettuce (cv. Vera) packaged in passive modified atmosphere

Abstract

Effect of a combined power ultrasound (US) and chlorine disinfection treatment on quality of fresh-cut ready-to-eat lettuce (cv. Vera) was evaluated. Fresh-cut lettuce was disinfected using 100mgL−1 NaOCl solution alone and in combination with ultrasound (130W, 42kHz) for different times (0–30min). Lettuce samples (80g) were then packaged in polypropylene (PP) film and stored at 5°C for 8 d. Application of US improved microbial reduction on processing day: an additional reduction in the range of 0.5–2.5logcfug−1 was obtained with respect to NaOCl treatment alone. Combined US-NaOCl application did not cause visual changes to lettuce neither on processing day nor when samples were stored under refrigerated conditions in passive modified atmosphere. Confocal images evidenced that US application could affect lettuce surface wax layer, removing its natural defense against microorganisms. This resulted in higher microbial growth throughout storage in samples treated with combined US-NaOCl treatment. US appears as a promising technique for fresh-cut produce disinfection, but further studies are needed to optimize US treatment to allow important microbial reductions throughout all storage time without compromising lettuce shelf life during refrigerated storage.