Biodegradable composite films based on kappa-carrageenan/locust bean gum blends and clays: Physical and antimicrobial properties

Biopolymer films offer a variety of advantages compared to synthetic films: biodegradability, use of renewable sources and potential edibility. Improvements in the functional properties of these films have been made by reinforcement of the polymer matrix with layered clay minerals such as montmorillonite. The aims of this work were to evaluate the physical and antimicrobial properties of biodegradable films composed by mixtures of kappa-carrageenan and locust bean gum (LBG) when organically modified clay (Cloisite 30B) was dispersed in the biopolymer matrix. Film forming solutions were prepared by adding Cloisite 30B (concentration ranging from 0 to 16% w/w) into the kappa-carrageenan/LBG solution (40/60% w/w) with 0.3% (w/v) of glycerol. Barrier properties (water vapor permeability, WVP ; CO 2 and O 2 permeabilities) and mechanical properties (tensile strength, TS and elongation at break, EB ) of the resulting films were determined. The composite film structure was investigated by X-ray diffraction (XRD). Antimicrobial effects of these films against Listeria monocytogenes , Escherichia coli, and Salmonella typhimurium were also evaluated. Results showed that an increase in the clay concentration caused a decrease of WVP from 5.34x10 -11 to 3.19x10 -11 g (m s Pa) -1 . O 2 permeability showed values ranging between 3.22x10 -14 and 4.80x10 -14 g (m s Pa) -1 . The CO 2 permeability increased from 2.26x10 -14 to 2.91x10 -14 g (m s Pa) -1 for films with 0 and 16% clay, respectively. Films with 16% clay exhibited the highest TS (33.82 MPa) and EB (29.82%). XRD patterns of the films indicated that a degree of exfoliation is attained depending on clay concentration. kappa-carrageenan/LBG/clay composite films exhibited an inhibitory effect only against L. monocytogenes due to the quaternary ammonium group of Cloisite 30B, which disrupts Gram-positive bacteria cell membranes. kappa-carrageenan/LBG/clay composite films are a promising alternative to synthetic films in order to improve the shelf-stability of food products.