Insights into pathogen inactivation and shelf-life extension of strawberries via combined ultrasound and levulinic acid treatment

Abstract

This study investigated the bactericidal effects of levulinic acid (LVA) and ultrasound against Listeria monocytogenes and analysed the corresponding metabolic response posttreatment via nuclear magnetic resonance (NMR) spectroscopy. The results suggested that the combined LVA and ultrasound treatment affected amino acid metabolism, energy metabolism, and osmotic and oxidative stress defense mechanisms in L. monocytogenes. This finding was supported by the reactive oxygen species (ROS) assay, which confirmed that the combined treatment intensified oxidative stress, leading to disrupted membrane integrity. To assess the broader antimicrobial efficacy of this combination and its application potential in food systems, the treatment was further evaluated on fresh strawberries using representative bacterial and viral surrogates. On fresh strawberries, the combined treatment reduced L. monocytogenes and all other tested bacterial groups to undetectable levels after washing (<2 log CFU g⁻¹). Significant inactivation was also observed for Tulane virus and bacteriophage MS2 (P < 0.05). Additionally, the application of ultrasound and LVA improved the physicochemical quality of strawberries during storage and significantly enhanced their antioxidant enzyme activities. This study highlights the potential of this combined treatment approach as a promising disinfection and preservation method for strawberries.