Keratin film for active packaging plasticized with citric acid

Innovative packaging materials have been the focus of extensive efforts extending the shelf-life of food, enhancing consumer safety, reducing wastes to the production sector, and being environmental friendly. Particularly, biopolymers such as lipids, proteins, polysaccharides and mixtures thereof, have been investigated to enhance the properties of films for packaging. Active packaging with antibacterial property is a concept in food technology based on incorporating an antimicrobial compound inside the packaging material or using a packaging material with inherent antimicrobial properties to reduce or inhibit microbial growth. In the present work, keratin and citric acid were mixed in water in order to produce a stretchable film with antibacterial properties for application in active packaging. Keratin is a natural protein that can be extracted from wool or other natural resources. Unfortunately, keratin alone has poor mechanical properties. Citric acid was employed as compatibilizer and plasticizer to improve the mechanical properties of films; it forms strong hydrogen bonds with hydroxyl groups and enhances interactions between macromolecules. In addition, citric acid has antibacterial properties and it is used in many different food products as preservative. The films obtained by blending keratin and citric acid showed excellent biocidal effect and high elongation value (600 %). Probably, the capability of citric acid to form hydrogen bonds is responsible for this great improvement of extensibility. On the other hand, the study of FT-IR spectrum allows to understand that the presence of citric acid in aqueous solution enhance the content of alpha helix structure in the film, with a reduction in the amount of side chain and disorder in the structure. Consequently, the high grade of the film elongation is possible because molecular structures are able to move freely in the film.