Abstract: Objective: The aim of this study was to explore the inactivation effect of high hydrostatic pressure (HHP) processing combined with lemon juice as a hurdle technology on naturally occurring microorganisms in soft packaged litchi and to do kinetic analysis. Methods: The numbers of aerobic bacteria, mold, yeast and Escherichia coli were measured by plate counting and the degree of swelling of packages was examined after synergistic treatment with different pressures (180, 380 and 500 MPa) and lemon juice concentrations (0%, 50% and 100%) for 5, 10 or 15 min, respectively. The Weibull model was used for kinetic analysis. Results: Microbial inactivation was improved with an increase in pressure level and processing time. In addition, the combined treatment more effectively inhibited the growth of the microorganisms than HHP alone. The inactivation effect of HHP at 380 MPa combined with 100% lemon juice on total aerobic bacteria was comparable to that of single HHP at 500 MPa. Both mold and yeast were more sensitive to high pressure processing and lemon juice with low acidity and could be completely inactivated by the above two treatment for 5 min. E. coli was undetected in the control group or the single HHP group. The packages subjected to the combined treatment with each lemon juice concentration or single HHP treatment for 15 min did no swell after storage at 37 ℃ for 7 days. The correlation coefficients (R2) of the survival curves for all treatment groups were more than 0.900, indicating that the Weibull model was suitable for the kinetic analysis of microbial inactivation. The scale factor b of the model increased with the increase of pressure and synergistic treatment with lemon juice, while the shape factor n decrease with the increase of pressure but slightly increased with synergistic treatment with lemon juice at the same pressure. Conclusion: The synergism of lemon juice combined with HHP can achieve high sterilization efficiency at lower pressures, which is beneficial to preserve the quality of soft-packed litchi fruits and prolong the storage period.

Key words: soft packaged litchi, high hydrostatic pressure, lemon juice, inactivation kinetics, Weibull model