Effective Bacterial Control during Fish Sauce Production under Pressurized CO₂

Abstract

　We aimed to achieve effective microbial control during fish sauce production under pressurized CO₂ (pCO₂) and investigated the combined bactericidal effect of lactic acid, acetate, NaCl, and pCO₂. Escherichia coli and Staphylococcus aureus were used as the test organisms. NaCl, acetic acid, and lactic acid concentrations were set to 7%, 0.005%-0.1%, and 0.1-0.5%, respectively, and pCO₂ treatment was performed at 37 ℃ and 1 MPa, for 30 min. The combined bactericidal effect of NaCl and 0.005% acetic acid present in the fish sauce was found to be less than 1 log₁₀ CFU/mℓ for both E. coli and S. aureus. Whereas, the combined use of salt and 0.15% lactic acid exerted a bactericidal effect on E. coli and S. aureus of 6.6 and 5.3 log₁₀ CFU/mℓ, respectively. Furthermore, the combined use of NaCl, pCO₂, acetic acid, and lactic acid inactivated approximately 7 log₁₀ CFU/mℓ in both bacterial species. Cell stainability by propidium iodide was enhanced following the combination treatment; however, the leakage of UV-absorbing substances was not observed in this analysis. From the results, we concluded that the bacteria are physiologically damaged and inactivated by the combined bactericidal effect of lactic acid, NaCl, and pCO₂ at the start of the fish sauce production process under pCO₂.