Physical properties and antilisterial activity of bioactive edible films containing Lactobacillus plantarum

Bioactive polymeric films were developed from the incorporation of Lactobacillus plantarum into polysaccharide or protein edible films. Lactic acid bacteria (LAB) were added directly to the film forming solution and films were obtained by casting. Four different biopolymers were tested: sodium caseinate, pea protein, methylcellulose and hydroxypropylmethylcellulose. In order to study the impact of the incorporation of the protective culture into the biopolymer matrix, the water vapour permeability (WVP), optical and mechanical properties of the dry films were evaluated. Furthermore, survival of L. plantarum and the antimicrobial potential of bioactive films against Listeria innocua were studied. Whereas optical and mechanical properties of the films were not notably altered by the LAB incorporation, WVP values increased for all biopolymers. Viability of the strain was lower in cellulose derivative matrices than in protein films, although bacteriocin production in the newly prepared films was greater in these matrices. As a result, a significant antimicrobial activity against L. innocua was observed for polysaccharide matrices, which was not observed for protein films, where the bacteriocin production is delayed. In pea protein films the maximum bacteriocin production occurs at 15 storage days and afterwards decreases. So, the nature of the biopolymer and the knowledge of time when an adequate bacteriocin concentration is produced are key to use bioactive films in an effective way.

Effect of bioactive films on the growth of Listeria innocua (a) on TSA medium, stored at 5 °C and survival of Lactobacillus plantarum in the film in contact with the culture medium (b). Mean values and 95% LSD intervals. (▴ PP + LAB, ♦ NaCas + LAB, ● MC + LAB, ■ HPMC + LAB, ▵ PP, ◊ NaCas, ˆ MC, □ HPMC and control in solid line).Figure optionsDownload as PowerPoint slideHighlights
► Bacterial cell incorporation into films provoked water vapour permeability increase.
► Viability of Lactobacillus plantarum was higher in protein than in cellulose films.
► Bacteriocin production was more retarded in protein than in cellulose films.
► Among newly prepared films, only cellulose films acted as effective antibacterial.
► Knowledge of time of adequate bacteriocin production is key to use bioactive films.