title: Fate of Staphylococcus aureus in cheese treated by ultrahigh pressure homogenization and high hydrostatic pressure.
abstract: We evaluated the influence of ultrahigh pressure homogenization (UHPH) treatment applied to milk containing Staphylococcus aureus CECT 976 before cheese making, and the benefit of applying a further high hydrostatic pressure (HHP) treatment to cheese. The evolution of Staph. aureus counts during 30 d of storage at 8 degrees C and the formation of staphylococcal enterotoxins were also assessed. Milk containing approximately 7.3 log(10) cfu/mL of Staph. aureus was pressurized using a 2-valve UHPH machine, applying 330 and 30 MPa at the primary and the secondary homogenizing valves, respectively. Milk inlet temperatures (T(in)) of 6 and 20 degrees C were assayed. Milk was used to elaborate soft-curd cheeses (UHPH cheese), some of which were additionally submitted to 10-min HHP treatments of 400 MPa at 20 degrees C (UHPH+HHP cheese). Counts of Staph. aureus were measured on d 1 (24 h after manufacture or immediately after HHP treatment) and after 2, 15, and 30 d of ripening at 8 degrees C. Counts of control cheeses not pressure-treated were approximately 8.5 log(10) cfu/g showing no significant decreases during storage. In cheeses made from UHPH treated milk at T(in) of 6 degrees C, counts of Staph. aureus were 5.0 +/- 0.3 log(10) cfu/g at d 1; they decreased significantly to 2.8 +/- 0.2 log(10) cfu/g on d 15, and were below the detection limit (1 log(10) cfu/g) after 30 d of storage. The use of an additional HHP treatment had a synergistic effect, increasing reductions up to 7.0 +/- 0.3 log(10) cfu/g from d 1. However, for both UHPH and UHPH+HHP cheeses in the 6 degrees C T(in) samples, viable Staph. aureus cells were still recovered. For samples of the 20 degrees C T(in) group, complete inactivation of Staph. aureus was reached after 15 d of storage for both UHPH and UHPH+HHP cheese. Staphylococcal enterotoxins were found in controls but not in UHPH or UHPH+HHP treated samples. This study shows a new approach for significantly improving cheese safety by means of using UHPH or its combination with HHP.
authors.affiliation: Centre Especial de Recerca, Planta de Tecnologia Dels Aliments, CeRTA, XiT, Departament de Ciència Animal I dels Aliments, Facultat de Veterinària, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
authors.forename: T
authors.initials: T
authors.lastname: López-Pedemonte
authors.forename: W J
authors.initials: WJ
authors.lastname: Brinez
authors.forename: A X
authors.initials: AX
authors.lastname: Roig-Sagués
authors.forename: B
authors.initials: B
authors.lastname: Guamis
mesh_terms: D000818:Animals; D002611:Cheese / Q000032:analysis / Q000382:microbiology*; D015169:Colony Count, Microbial; D003612:Dairying / Q000379:methods*; D004768:Enterotoxins / Q000032:analysis; D005511:Food Handling / Q000379:methods*; D006874:Hydrostatic Pressure; D008892:Milk / Q000382:microbiology; D011312:Pressure; D013211:Staphylococcus aureus / Q000302:isolation & purification / Q000502:physiology*; D013696:Temperature; D013997:Time Factors
chemical_list: D004768:Enterotoxins