Ultrasound Improves the Decontamination Effect of Thyme Essential Oil Nanoemulsions against Escherichia coli O157: H7 on Cherry Tomatoes

Authors: HE, QIAO - Zhejiang University; GUO, MINGMING - Zhejiang University; Jin, Zhonglin; ARABI, SAIFANASSOUR - The Jm Smucker Company; LIU, DONGHONG - Zhejiang University

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2020
Publication Date: 1/16/2021
Citation: He, Qiao, Guo, Mingming, Jin, Z.T., Arabi, S.A., Liu, D. 2021. Ultrasound improves the decontamination effect of thyme essential oil nanoemulsions against Escherichia coli O157: H7 on cherry tomatoes. International Journal of Food Microbiology. 337:108936. https://doi.org/10.1016/j.ijfoodmicro.2020.108936.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2020.108936

Interpretive Summary: The microbiological safety of fresh produce has gained considerable attention, due to many related foodborne outbreaks. This study investigated the antimicrobial effect of ultrasound in combined with thyme essential oil nanoemulsion washing against E. coli O157:H7 on cherry tomatoes. Remarkable synergistic effects of the combined treatments were achieved, which decontaminated the E. coli populations on the surface of cherry tomatoes by more than 99.99%. The treatments did not noticeably alter the surface color and firmness of cherry tomatoes. Ultrasound combined with thyme essential oil nanoemulsion is a promising and feasible alternative for minimal processing industry to improve fresh produce safety.

Technical Abstract: Development of novel and effective decontamination technologies to ensure the microbiological safety of fresh produce has gained considerable attention, mainly driven by numerous outbreaks. This work presented the first approach regarding to the application of the previously reported hurdle technologies on the sanitization of artificially contaminated cherry tomatoes. Thyme (Thymus daenensis) essential oil nanoemulsion (TEON, 8.28 nm in diameter with a narrow size distribution) was formulated via ultrasonic nanoemulsification, showing remarkably improved antimicrobial activity against Escherchia coli O157:H7, compared to the coarse emulsion. The antimicrobial effect of ultrasound (US), thyme essential oil nanoemulsion (TEON) and the combination of both treatments was assessed against E. coli O157:H7. The remarkable synergistic effects of the combined treatments were achieved, which decontaminated the E. coli populations by 4.49-6.72 log CFU/g on the surface of cherry tomatoes, and led to a reduction of 4.48-6.94 log CFU/sample of the total inactivation. TEON combined with US were effective in reducing the presence of bacteria in wastewater, which averted the potential detrimental effect of cross-contamination resulted from washing wastewater in fresh produce industry. Moreover, the treatments did not noticeably alter the surface color and firmness of cherry tomatoes. Therefore, ultrasound combined with TEON is a promising and feasible alternative for the reduction of microbiological contaminants, as well as retaining the quality characteristics of cherry tomatoes.