Abstract: In order to explore the bactericidal effect of high hydrostatic pressure on natural microorganisms in fresh apple juice, the numbers of total bacteria, mold and yeast in fresh apple juice were measured after pressure treatment at 300, 400, 500 or 600 MPa for 5, 10, 15, 20 min and 25 min, respectively. The results showed that the bactericidal effect was improved with the increase of pressure level and pressure-holding time. Mold and yeast were more sensitive to high hydrostatic pressure and could be inactivated at 500 MPa for 5 min. The Weibull model was used to fit the survival curve. The correlation coefficients (R2) were more than 0.900 determined at four pressure levels, which proved that Weibull model was suitable for the kinetic analysis of bacterial inactivation. The values of scale factor b in the model were increased with the increase of pressure, while the values of shape factor n were stable in the pressure range of 400 to 600 MPa.

Key words: high hydrostatic pressure, fresh apple juice, total bacterial count, mold, yeast, Weibull model