Inactivation of foodborne pathogens based on synergistic effects of ultrasound and natural compounds during fresh produce washing

• Published in: Ultrasonics sonochemistry Vol. 64; p. 104983
• Main Authors: Zhang, Hongchao, Wang, Siyuan, Goon, Kasey, Gilbert, Andrea, Nguyen Huu, Cuong, Walsh, Martin, Nitin, Nitin, Wrenn, Steven, Tikekar, Rohan V.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2020
• Subjects: Acyclic Monoterpenes - pharmacology; Blueberry Plants - drug effects; Blueberry Plants - microbiology; Citral; Escherichia coli K12 - drug effects; Escherichia coli K12 - physiology; Food Handling - methods; Food Microbiology; Foodborne pathogen; Fresh produce sanitation; Listeria - drug effects; Listeria - physiology; Microbial Viability - drug effects; Natural compounds; Synergistic effect; Ultrasonic Waves; Ultrasound; Fresh produce sanitation; Synergistic effect; Natural compounds; Ultrasound; Citral; Foodborne pathogen
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2020.104983

•Synergistic combined treatments result in 0.5–2.0 log additional bacteria reduction.•20 kHz US enhance inactivation mainly by physical impact and dispersion of citral.•1 MHz US enhance inactivation mainly by inducing oxidative stress.•Treatments in high organic load water or on blueberries shows additive effects.•No significant changes in blueberries were visually observed after treatments. Ultrasound has potential to be used for disinfection, and its antimicrobial effectiveness can be enhanced in presence of natural compounds. In this study, we compared the antimicrobial effects of ultrasound at 20 kHz (US 20 kHz) or 1 MHz (US 1 MHz) in combination with carvacrol, citral, cinnamic acid, geraniol, gallic acid, lactic acid, or limonene against E. coli K12 and Listeria innocua at a constant power density in water. Compared to the cumulative effect of the individual treatments, the combined treatment of US 1 MHz and 10 mM citral generated >1.5 log CFU/mL additional inactivation of E. coli K12. Similarly, combined treatments of US 1 MHz and 2 mM carvacrol (30 min), US 20 kHz and 2 mM carvacrol, 10 mM citral, or 5 mM geraniol (15 min) generated >0.5–2.0 log CFU/mL additional inactivation in L. innocua. The synergistic effect of citral, as a presentative compound, and US 20 kHz treatment was determined to be a result of enhanced dispersion of insoluble citral droplets in combination with physical impact on bacterial membrane structures, whereas the inactivation by US 1 MHz was likely due to generation of oxidative stress within the bacteria. Combined ultrasound and citral treatments improved the bacterial inactivation in simulated wash water in presence of organic matter or during washing of inoculated blueberries but only additive antimicrobial effects were observed. Findings in this study will be useful to enhance fresh produce safety and shelf-life and design other alternative ultrasound based sanitation processes.