Use of Desirability Approach to Predict the Inhibition of Pseudomonas fluorescens, Shewanella putrefaciens and Photobacterium phosphoreum in Fish Fillets Through Natural Antimicrobials and Modified Atmosphere Packaging

The main goal of this paper was the prolongation of the microbiological acceptability limit (MAL) of gilthead sea bream fillets, added with some natural antimicrobials and packed under modified atmosphere; desirability approach was used, and the research was divided into two different steps. The first phase addressed fish fillet preservation through chitosan (0–4 %), grape fruit seed extract (GFSE) and thymol (0–6,000 ppm); Pseudomonas fluorescens, Shewanella putrefaciens and Photobacterium phosphoperum, inoculated onto the surface of fillets, were used as microbial targets. The concentration of the three antimicrobials were combined through a three variables/five levels central composite design; after fish inoculation and dipping into active solutions containing the natural compounds, fillets were stored at 4 °C and analysed periodically. Data of microbiological counts were fitted through a primary model (modified Gompertz equation), for the evaluation of MAL; MALs were used to build a polynomial model, able to draw a desirability profile for each antimicrobial. These outputs (desirability and polynomial equation) highlighted that Pseudomonas fluorescens was the most resistant microorganism; it could be inhibited through an active solution containing 2 % of chitosan and 6,000 ppm of GFSE and thymol. Therefore, in the second step of the research, fish fillets were dipped in this active solution and packed under two different atmospheres (30:40:30 O₂/CO₂/N₂ and 5:95 O₂/CO₂) and stored at 4 °C. For each microorganism, the stability time was evaluated, thus pointing out that the best sample was that packed under 5:95 O₂/CO₂.