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Bioactive film can help keep strawberries fresh longer

Quebec researchers have developed a bioactive film containing crustacean shells and antimicrobial nanoparticles, which can be used to keep fruit fresher for longer.

Strawberries and other soft fruits are delicate and difficult to keep fresh. To preserve them longer and prevent food waste, Professor Monique Lacroix of the Institut National de la Recherche Scientifique (INRS) led the development of a packaging film to preserve freshness.

The packaging protects against mold and certain disease-causing bacteria and can keep strawberries fresh for up to 12 days. The film is made from chitosan, a natural molecule found in the shell of crustaceans and can be considered a by-product of the food industry.

The fabric contains important anti-fungal properties that can be used to curb mold growth. The film also contains essential oils (concentrates of botanical aroma compounds) and synthesized silver nanoparticles, both of which have antimicrobial properties.

Silver nanoparticles adhere to the cell wall and membrane of a bacterium; silver can penetrate the bacteria. The chemical reactions caused by the introduction of silver cause the DNA to condense, preventing replication and causing cell death.

Silver nanoparticles are used, among other things, to develop wound dressings that prevent infections.

“Essential oil vapors protect strawberries, and when the film comes into contact with strawberries, the chitosan and nanoparticles prevent fungi and pathogens from reaching the surface of the fruit,” said Lacroix, who led the study.

The composite film has the advantage of being effective against various types of pathogens when used in conjunction with a standard irradiation process, which kills microbes on the strawberries before packaging.Lacroix and her INRS colleagues tested it on four microbial cultures:

Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and Aspergillus niger. The composite films showed strong antimicrobial activity against all. This is particularly good news regarding Aspergillus niger, a highly resistant fungus that is responsible for significant losses during strawberry production.

The other three pathogens come from contamination during food handling and are a concern for the food industry.

They found that the combination of irradiation and packaging resulted in a much longer shelf life, halving the level of loss compared to the control. On day 12, they recorded a 55 percent loss for the control group; 38 for the group with the film alone, and 25 percent with the film and radiation.

Irradiation not only extends the shelf life; it also helps to maintain or increase the amount of polyphenols in the strawberries (the antioxidant molecules responsible for giving strawberries their color).

The researchers suggest that the composite film could be inserted into the tissue paper that the industry currently uses to store strawberries.