A comparison of the bactericidal effectiveness of hydrochloric and acetic acid on Staphylococcus aureus in silver carp during a pH-shift protein recovery process

Abstract

The bactericidal effectiveness of a pH-shift protein recovery process was tested against Staphylococcus aureus. Protein from ground silver carp inoculated with S. aureus was solubilized at pH 2.5, 3.0, 11.5, or 12.5 with the addition of glacial acetic acid (AA), hydrochloric acid (HCl) or sodium hydroxide. Lipid and other insoluble components (bone, skin and so on) were removed by centrifugation. Solubilized protein was brought to the isoelectric point (pH 5.5) with the addition of acid or base. Microbial analysis was performed on all fractions and survivors were enumerated on Baird Parker and Tryptic Soy Agar media. No significant differences in recovery were observed (P > 0.05) between media in the protein, lipid and water fractions. The main effect of acid type did not have a significant (P > 0.05) impact on microbial reductions for any fraction; however, significant reductions occurred as a function of protein solubilization pH (P < 0.0001) with basic solubilization strategies being most effective. The greatest reductions (P < 0.05) occurred in the protein fraction when protein was solubilized at pH 12.5 and precipitated with acetic acid for a 2.50 log reduction in the protein fraction. These results show that the pH-shift protein recovery process will significantly reduce S. aureus.