US-INACTIVATION of foodborne bacteria: Screening in distilled water and combination with citrus extract in skim milk

The paper reports on the use of US (ultrasound) as a tool to control the growth of foodborne bacteria. Seventeen microorganisms were inoculated in distilled water, treated by US and the number of survivors was assessed immediately after the treatment; power (20-80%), duration (2-8 min) and pulse (2-6 s) varied according to a fractional design. The results were modeled using a multifactorial ANOVA. Data pinpointed the existence of different levels of resistance/susceptibility, being Staphylococcus spp., and Pseudomonas putida the most resistant microorganisms; moreover, power and time played a major role, whilst pulse was less significant. In a second experiment Ps. putida and Staphylococcus spp. were used as targets for a challenge test in skim milk; a commercial and odorless citrus extract (50 or 100 ppm) was added to control the growth of survivors within the storage at 4 °C. US (80% of power/8 min) acted as a tool in reducing the initial contamination; whilst citrus extract (100 ppm) assured the antibacterial effect of US on Staphylococcus spp. within the storage.