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Researchers show natural microbial agents in packaging can extend shelf life of salmon

By Joe Whitworth , 26-Nov-2012
Last updated on 26-Nov-2012 at 15:19 GMT

Researchers show active packaging can extend shelf life of salmon

Researchers in Chile have invented a system incorporating natural microbial agents in a polymeric structure aimed at increasing the shelf life of refrigerated fresh salmon.

Abel Guarda et al said it could offer shelf life increases of up to four days depending on storage temperature.

The application was made by Guarda, Ximena Valenzuela, Alberto Ramirez and Jose Maria Galotto from the Universidad de Santiago de Chile to the European Patent Office .

How it works?

Incorporation of the active ingredient is carried out through a first extrusion process which allows a pellet (masterbatch) to be obtained, followed by a second co-extrusion allowing the masterbatch to be put into the inner face of the film which is in direct contact with the food.

The film is obtained through a coextrustion process and only the inner layer will be in direct contact with the salmon which is where the masterbatch containing the active compound is added.

The third layer is composed of 90% low densitty polyethylene (LDPE) and 10% with the active agent.

The masterbatch containing 10% of antimicrobial agent is mixed with LDPE at different concentrations between 0.5 and 15%.

The team said: “There is a possibility of using volatile natural compounds with antimicrobial properties that can be incorporated into the package, but it is necessary to determine the appropriate mechanism for incorporating these agents in the plastic structure so as to exert its function directly on the food surface, maintaining this function during the time the product will be packed and stored.”

Step-by-step

The process was described in the application under three steps:

  • mixing a first extrusion of the antimicrobial active agent thymol with low density polyethylene powder to obtain a pellet;
  • a second extrusion to obtain a film incorporating the pellet obtained in step one in a proportion of 10% polyethylene pellets;
  • conduct a three-layer coextrusion to develop the film into which the antimicrobial agent is incorporated, wherein the antimicrobial active agent is incorporated into the film layer which is in direct contact with salmon, where the binder, the middle and the outer structure of the film, provide the requirements for the film structure, without the incorporation of the active agent.

Pathogen tests

Animicrobial effectiveness was measured with E.coli, where a reduction of 100% was shown after 24 hours providing the concentration of microbial in the films was more than 10%.

Reduction of listeria at 24 hours was more than 99% and a final effective concentration in the film of only 0.46%.

A chemical analysis, demonstrated results between the active packaging and a control, decreased with temperature but it can offer difference of four days, according to the patent.

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