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

•US (130W, 42kHz) improved microbial reduction in disinfection of fresh-cut lettuce.•Increasing US application time resulted in higher microbial reductions.•US disinfected lettuce showed faster microbial growth throughout 8 d storage at 5°C.•US affected lettuce surface wax layer, removing its defense against microorganisms.•US application did not cause visual changes on lettuce throughout storage at 5°C.