Inactivation of Escherichia coli O157:H7 and Salmonella spp. in strawberry puree by high hydrostatic pressure with/without subsequent frozen storage.

The objectives of this study were to investigate the survival of Escherichia coli O157:H7 and Salmonella spp. in frozen strawberry puree and to assess the application of high pressure processing (HPP) to decontaminate strawberry puree from both pathogens. Fresh strawberry puree was inoculated with high (~6 log CFU/g) and low (~3 log CFU/g) levels of E. coli O157:H7 or Salmonella spp. and stored at -18°C for 12 weeks. Both pathogens were able to persist for at least 4weeks and samples with high inoculums were still positive for both pathogens after 12 weeks. Pressure treatment of 450 MPa for 2 min at 21°C was able to eliminate both pathogens in strawberry puree. Frozen storage at -18°C after pressure treatment substantially enhanced the inactivation of both pathogens and 4-8 days of frozen storage was able to reduce the pressure level needed for elimination of both pathogens to 250-300 MPa. Natural yeasts and molds in strawberry puree were effectively reduced by pressure of 300 MPa for 2 min at 21°C. No adverse impacts on physical properties such as color, soluble solids content, pH and viscosity of strawberry puree was found for pressure-treated samples. Therefore, the treatment of 300 MPa for 2 min at 21°C followed by 4 days frozen storage at -18°C was recommended for the minimal processing of strawberry puree with great retention of fresh-like sensory properties. HPP could be a promising alternative to traditional thermal processing for berry purees.