Antibacterial mechanism of ultrasound combined with oregano essential oil nano-emulsion on Escherichia coli O157:H7 and application in cherry tomatoes storage

Abstract

Escherichia coli (E. coli) O157:H7 on the surfaces of fruits and vegetables poses significant risks to human health. This study assessed the bactericidal mechanisms of ultrasound (US) and oregano essential oil nanoemulsion (OEON) against E. coli, as well as their application in storage preservation of cherry tomatoes. The results showed that US + OEON treatment exhibited markedly superior inactivation effect on E. coli compared to their individual treatments. OEON (2 %) combined with ultrasonic treatment (375 W) for 4 min reduced the viable E. coli count by 5.06 ± 0.22 log CFU/mL. This performance markedly exceeded that of single treatments, with US achieving 1.15 ± 0.10 log CFU/mL reduction and OEON 1.04 ± 0.18 log CFU/mL reduction. The synergistic treatment intensified lipid peroxidation of bacterial cell membranes and enhanced membrane permeability. Furthermore, in preservation applications on cherry tomatoes, US + OEON effectively suppressed total viable counts, achieving a 1.44 ± 0.19 log CFU/mL reduction after 4-min treatment with 2 % OEON combined with 375 W US. This approach induced no adverse effects on cherry tomato color, texture, nutritional composition, or antioxidant properties. In summary, compared to US or OEON treatment alone, US + OEON treatment exhibits superior antibacterial effect and improves the storage quality of cherry tomatoes.