Bactericidal effects of high hydrostatic pressure treatment singly or in combination with natural antimicrobials on Staphylococcus aureus in rice pudding

Abstract

Inactivation of Staphylococcus aureus strains by high hydrostatic pressure (HHP) treatments applied singly or in combination with natural antimicrobials (nisin, enterocin AS-48, cinnamon oil and clove oil) was investigated in rice pudding. Treatments at 600 MPa for 10 min reduced initial populations of staphylococci (7.9 log CFU/g) below detectable levels of 1 log CFU/g in the puddings. Treatments at 500 MPa for 5 min (achieving a 2.9-log reduction of viable counts) were investigated singly or in combination with nisin (200 and 500 IU/g), enterocin AS-48 (25 and 50 μg/g), cinnamon oil (0.2%, vol/wt) or clove oil (0.25% vol/wt). The combined treatment of enterocin AS-48 (50 μg/g) and HHP caused a non-significant reduction of 0.4–0.6 log cycles compared to HHP alone. Additional reductions of 0.87, 1.3 and 1.8 log cycles were recorded for the combined HHP treatments with nisin (500 IU/g), cinnamon oil (0.2%) and clove oil (0.25%), respectively. During refrigeration storage for one week, viable counts in puddings from combined treatments were significantly lower compared to the single HHP treatments, e.g. 1.5–2.7 log cycles for HHP-nisin (500 IU/g), 1.1–1.3 log cycles for HHP-AS-48 (50 μg/g) or approx. 1.5 log cycles for HHP-cinnamon oil (0.2%). These results suggest that the time and intensity of HHP treatments required for inactivation of S. aureus in puddings can be reduced when HHP is applied in combination with selected natural antimicrobials.