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°C and the formation of staphylococcal enterotoxins were also assessed. Milk containing approximately 7.3 log10 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 (Tin) of 6 and 20°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°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°C. Counts of control cheeses not pressure-treated were approximately 8.5 log10 cfu/g showing no significant decreases during storage. In cheeses made from UHPH treated milk at Tin of 6°C, counts of Staph. aureus were 5.0 ± 0.3 log10 cfu/g at d 1; they decreased significantly to 2.8 ± 0.2 log10 cfu/g on d 15, and were below the detection limit (1 log10 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 log10 cfu/g from d 1. However, for both UHPH and UHPH+HHP cheeses in the 6°C Tin samples, viable Staph. aureus cells were still recovered. For samples of the 20°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. © American Dairy Science Association, 2006.
|Journal||Journal of Dairy Science|
|Publication status||Published - 1 Jan 2006|
- High hydrostatic pressure
- Staphylococcus aureus
- Ultrahigh pressure homogenization