Recovery of Salmonella spp. from Raw Produce Surfaces Using Ultrasonication

Fresh fruits and vegetables have been increasingly associated with outbreaks of foodborne illness. Microorganisms on the surface of raw produce may be difficult to remove for decontamination or microbial sampling due to entrapped or attached cells and porous surfaces. The objective of this study was to determine if ultrasonic treatment using 40 kHz with varying temperatures and agitation times can enhance removal and recovery of Salmonella spp. from raw produce surfaces. Strawberry, apple, and cantaloupe surfaces were spot inoculated with a fivestrain cocktail of nalidixic acid–resistant Salmonella spp. Produce were immersed in 0.1% buffered peptone water in either a Whirl-Pak bag for manual shaking (60 sec) or a sterile beaker for ultrasonic treatment (60 or 120 sec). Diluent temperatures of either 25°C or 40°C were used with these sampling protocols. Diluents were spiral plated onto tryptic soy agar supplemented with 50 ppm of nalidixic acid. No significant differences were observed between each Salmonella recovery method for each produce type. In this study, ultrasonic treatment using 40 kHz did not enhance recovery of Salmonella spp. from produce surfaces. The ultrasonic frequency, temperatures, and times used in this study did not enhance or diminish bacterial recovery. Additional research is still needed to determine the efficacy of other ultrasonic frequencies, diluents, and diluent temperatures for enhancing the recovery and enumeration of Salmonella spp. and other microorganisms from raw produce surfaces.