Note. Reaction of Bacteria Associated with Fish Spoilage to Chemical and Physical Stress

Abstract

A cocktail made up of six bacteria isolated from fish was subjected to various heats (30 °C and 60 °C, 20 s) and chemical preservative stresses, alone and in combination. The chemical preservatives tested were potassium sorbate (PS, 1%), trisodium phosphate (TSP, 10%) and tetrasodium pyrophosphate (TSPP, 3%). Heating the bacteria at 60 °C for 20 s resulted in an average reduction of 2.0 log cfu/mL in the total number. The results showed amarked synergistic effect of heat treatment prior to chemical additives, especially for TSPP and sorbate; no significant effect was evident when chemicals were applied alone. The effect was increased by the application of chemical preservatives, before heating, in the decreasing order TSP, TSPP and sorbate; reductions obtained were more than 5.0, 4.0 and 3.0 log cfu/mL, respectively. The synergistic effect observed was dependent on the type of chemical additives used and also on the order of the treatments. Bacteria identified as Shewanella putrefaciens and Pseudomonas putida were more resistant to heat treatment and Brochothrix thermosphacta and Lactobacillus plantarum were more resistant to TSP treatment. These bacteria in the cocktail showed high sensitivity to combined TSP/heat treatment; bacterial cells identified as Enterobacter spp. were the most resistant to this treatment.