Survival data of Escherichia coli O157:H7 933 and Staphylococcus aureus 485 in carrot juice and peptone water were collected in a range of pressure levels between 200 and 400 MPa at 40 degrees C. A mathematical approach combining the primary and secondary models (Weibull and first-order models as the primary model and two empirical equations as the secondary model) was proposed to estimate the microbial parameters using nonlinear least squares procedure in one step, resulting a single equation. Although not perfectly matched with the survival data, the proposed model produced good fits. Better fits were observed for S. aureus than for E call. Simulations of 5log(10) reductions of both pathogens indicated that carrot juice had a protective effect on E. coli whereas it had a sensitizing effect on S. aureus. The development of such mathematical models would be very beneficial to the food industry by developing safe processing conditions for HHP processing of foods. (C) 2008 Elsevier Ltd. All rights reserved.