Purpose: The purpose of this study was to identify the efficiency of HPP to inactivate Salmonella spp. and Enterococcus faecium (commonly used surrogate for Salmonella) in strawberries and blueberries.
Methods: Fresh strawberries and blueberries were spot-inoculated with approximately 6 log CFU/g of Salmonella or E. faecium. Berries were vacuum-sealed in high barrier pouches, packaged (fresh or frozen) and treated at varying pressure levels (250, 300, 350, 400 and 600 MPa) for 3 minutes at an initial temperature of 4°C. Visual analyses were conducted pre- and post- HPP for sensory assessment. Enumeration was performed using non-selective tryptic soy agar with 0.6% yeast extract (TSAYE), followed by a xylose lysine desoxycholate (XLD) overlay for Salmonella and m-Enterococcus agar overlay for E. faecium.
Results: HPP inactivation of Salmonella in strawberries demonstrated gradual inactivation as pressure levels increased, with 5.8 ± 0.6 and 4.9 ± 0.9 log CFU/g reduction at 600 MPa for fresh and frozen, respectively. Salmonella inactivation in fresh and frozen blueberries demonstrated an increase in inactivation at 600 MPa, fresh blueberries had a log reduction of 4.3 ± 1.1 log CFU/g compared to frozen with 2.5 ± 0.2 log CFU/g. Surrogate microorganism, E. faecium, demonstrated resistance to HPP inactivation, with less than 1 log CFU/g reduction at 600 MPa.
Significance: These results suggest application of HPP on fresh and frozen berries is an effective method for the inactivation of Salmonella, however, E. faceium may not be an appropriate surrogate for Salmonella to assess HPP efficacy.