Application of nisin, CO2 and a permeabilizing agent in the preservation of refrigerated blue whiting (Micromesistius poutassou)

Abstract

Gram-negative bacteria aremainly responsible for spoilage of refrigerated fish. Nevertheless, to preserve refrigerated fresh fish no additives are permitted and only packaging as in a modified atmosphere can be used. Despite the fact that the present-day application of nisin has been extended to dairy and meat products, its ineffectiveness against Gram-negative bacteria complicates application to fresh fish unless combined with other additives such as chelators. With this aim, agents that increase the permeability of the membrane and facilitate the diffusion of many hydrophobic antimicrobial agents were screened for their combined activity with nisin against different genera of Gram-negative bacteria. Quantification of the synergistic effects has shown sodium hexamethaphosphate (SMP) and ethylenediaminetetraacetic acid (EDTA) were themost effective. Further studies were done on the combined effects of nisin, SMP and CO2 in the preservation of fresh fish. A factorial experimental design was used to determine synergism between these variables. Logarithmic values of total viable counts and total volatile bases after 12 days of storage were described by empirical equations. Analysis of the results showed a marked effect of CO2 in decreasing both variables. Whereas CO2 interacted positively with nisin and SMP, a non-significant interaction was observed between nisin and SMP. It is concluded that CO2 interacts readily with SMP, and may offer an additional advantage for CO2-rich atmospheres in food preservation.