Biopolymers

In recent years, bio-based products have raised great interest since sustainable development policies tend to expand with the decreasing reserve of fossil fuel and the growing concern for the environment. Biopolymers based on renewable resources present a noteworthy potential to retain and release active compounds (Cha and Chinnan, 2004), and these materials can be employed in the development of antimicrobial films both to extend the shelf life of food and to contribute to the protection of environment by use of environmentally friendly materials. Most of the studies of biopolymers in antimicrobial packaging of dairy products are related with agro-polymers like chitosan, cellulose, wheat gluten, zein, and starch, and all of them are obtained by extracting directly from natural renewable resources. Chitosan is a well-known and mostly studied film-forming biopolymer obtained from crustacean shells. It has shown antimicrobial activities against different groups of microorganisms including bacteria and fungi. Chitosan can be used in antimicrobial packaging as a film or coating with/without enrichment with essential oils, enzymes, bacteriocins, etc. and applied as a microbial hurdle in variety of cheeses and other dairy products.

In a study, antimicrobial efficacy of chitosan or chitosan enriched with essential oils (oregano oil or clove oil) coated on PP (Polypropylene) films were evaluated against Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli on Kashar cheese at 4°C (Torlak and Nizamioglu, 2011). It was observed that the films containing oregano oil but not clove oil had significant antibacterial activity against E. coli. Duan et al. (2007) investigated the antimicrobial activities of chitosan films incorporated with lysozyme and chitosan coatings against E. coli, Pseudomonas fluorescens,

L.monocytogenes, yeast, and mold inoculated onto the surface of Mozzarella cheese at 10°C. Growth of these bacteria and mold were significantly inhibited in cheese packaged with chitosan-lysozyme films, although they had lesser antimicrobial effect on yeast. Lysozyme enhanced the antimicrobial efficacy of chitosan films and coatings against P.fluorescens and L.monocytogenes. Dos Santos Pires et al. (2008) studied with biodegradable cellulose films containing nisin, natamycin, and combination of both against microorganisms on sliced Mozzeralla cheese. The films containing natamycin were able to inhibit yeast and mold growth whereas films containing nisin were able to delay psychrotrophic bacteria growth. But combination nisin+natamycin did not show a synergistic effect in cheese. Balaguer et al. (2013) succeeded in extending the shelf life of cheese spread from 16 days to 33 days by inhibiting fungal growth with gliadin- (a protein group of wheat gluten) based antimicrobial films incorporated with 5% cinna- maldehyde. The same researchers incorporated 0.5% natamycin into gliadin films treated with cinnamaldehyde and evaluated the antifungal effectiveness of the films for different kinds of cheese (Balaguer et al., 2014). While this antimicrobial packaging system totally inhibited fungal growth on the surface of soft cheese, for semi-hard cheese only the limited inhibition was observed. But natamycin did not exert an additional antifungal effect. Unalan et al. (2013) showed the efficacy of lysozyme to prevent the growth of L.monocytogenes in Kashar cheese packaged with zein or zein-wax composite films. Kuorwel et al. (2014) investigated the antifungal activity of active constituents derived from essential oils (EO) -linalool, carvacrol and thymol incorporated in to the coatings of starch-based films on Cheddar cheese against Aspergillus niger. Prabhawathi et al., (2014) studied with polycaprolactam, which is a petroleum-based biopolymer produced by conventional synthesis from synthetic monomers. They showed that papain, which is a proteinase isolated from papaya immobilized on polycaprolactam, could be used to control the growth of E. coli on cottage cheese.

 
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