Swelling kinetics of dried edible composite films based on gum tragacanth and gelatin in distilled water and salt solution

Food biopolymers have notably been utilized in creating edible composites with unique properties for food and drug applications. Edible composite films can be fabricated using multiple biopolymers, where protein-protein, protein-polysaccharide, and polysaccharide-polysaccharide interactions are the major determinants of their micro- and macro behaviors. The extent of interaction depends on several factors, including the nature of biopolymers, concentration, preparation method and conditions. This study prepared model systems composed of binary biopolymer blends by mixing gum tragacanth (0.1, 0.5, and 1% v/w) and gelatin (0.9, 4.5, and 9% w/v) solutions at equal proportions to study the effect of different swelling media (distilled water and 0.5 M CaCl₂ solution). Their rheological properties were analyzed. The films were prepared by casting the binary biopolymer solutions at pH 4 in Petri dishes (5-20 mL) followed by 48 h dehydration in a fume hood. Film characterization experiments included dimensional analysis, moisture content, and morphology. Their swelling kinetics in two different media were obtained within 1 h (0, 10, 20, 40, and 60 min) and overnight swelling. Gel-like and viscous-like behaviors were observed for the film-forming solutions, which affected their film-forming abilities. The thickness and weight of the films were in the range of 0.10 ± 0.02 to 0.90 ± 0.02 mm and 0.10 ± 0.01 to 0.70 ± 0.01 g, respectively. The moisture content of the films was 6.98 ± 0.33 % (wb). Increasing biopolymer concentration resulted in increased swelling capacity with altered swelling rates due to micro- and macrostructures of the film matrix in two different media. Photomicrographs of the film cross-sections proved the film matrix effects on the swelling rates. The results presented in this study may help researchers design and produce novel edible composites with enhanced functional performance depending on the intended film application.