A novel sodium alginate active films functionalized with purple onion peel extract (Allium cepa)

The purple onion peel extracts (POPE) have a high content of phenolic compounds and can be used as a promising strategy in the development of active packaging. Biodegradable sodium alginate films have good characteristics of gel formation, flexibility, transparency, brightness, and low oil permeability. The incorporation of bioactive compounds from plant residues can be a low-cost technique to functionalize alginate-based materials. The aim of this work was to evaluate the effects of POPE incorporation on the physical, mechanical, barriers, antioxidants, and antimicrobial properties of alginate-based films. Filmogenic solutions were prepared with a concentration of 0, 10, 20, and 30% of POPE and glycerol was used as plasticizer. The addition of POPE in the sodium alginate matrix promoted the development of opaque red films, with a content of phenolic compounds 43 times greater than the film without extract. As expected, the incorporation of POPE increased the antioxidant activity and the thickness of the alginate-based films. In addition, the incorporation of phenolic compounds promoted better interaction between the polymeric networks, reducing the water solubility of the alginate films. The results indicated that the sodium alginate films incorporated with several concentration of POPE have been shown to be an interesting material for the production of active packaging, being possible to apply them in foods with high water activity or susceptible to lipid oxidation, to preserve and extend the shelf life of these products.