CARBOXYMETHYLCELLULOSE IMPROVES PROPERTIES OF SOY PROTEIN ISOLATE BASED FILM

Edible films are composed of biological materials such as proteins and polysaccharides. Through the synergistic interactions between film components, those containing more than one biopolymer in their composition have been used to produce composed edible films with improved physicochemical properties when compared to those formed by the pure biopolymers. The aim in the present study was to evaluate the effect of the interaction between carboxymethylcellulose (CMC) and soy protein isolate (SPI) on the mechanical and water vapor properties of edible films. For this, films were formed from pure biopolymers at concentrations of 0.5% for CMC films (without pH adjustment) and 5% for SPI films (pH 11). The composed films were prepared by mixing the CMC and SPI solutions and adding distilled water in adequate proportions to ensure that the final film-forming solution was composed of fixed concentrations of 5% SPI (w/w) and 0.5% CMC (w/w). Glycerol was used as plasticizer in a proportion of 30% (in relation to CMC) for pure CMC solutions and of 40% (in relation to SPI) for single-SPI solutions and SPI/CMC mixtures. The film-forming solutions were poured on smooth plane molds and dried at 35 °C in a BOD incubator chamber (BT-71, Biothec, Brazil). Films’ water vapor permeability (WVP) was determined in triplicate from three different films of each formulation according to the ASTM E96-95 standards. Mechanical properties (ASTM D882-12) were evaluated from six distinct films of each formulation, of which at least ten specimens were randomly chosen to perform the analysis. The WVP, determined under an average relative humidity of 50% RH, remained in the order of 10-10 (g∙m-1∙s-1∙Pa-1). A significant difference was observed between the films made from the pure biopolymers, while CMC addition did not significantly alter the WVP of the single-SPI film. The WVP of single-CMC films resulted in approximately 4 to 5 times lower than that of SPI-based films. Regarding mechanical performance, tensile strength ranged from approximately 18.5 MPa for CMC-based films to 3 (SPI-CMC) or 2 (single SPI) MPa for SPI-based films. However, the elongation at break of the single-CMC film was very low (≈6.0%), while SPI-based films presented values approximately 25 times greater than the former. Although the single-CMC films have shown good resistance, their poor ductility makes them very fragile. The addition of CMC to SPI film modified its structure, which can be attributed to several factors, such as the excluded volume effect, which contributes to reinforcing the protein network, or even such as the role of CMC as a filling agent of the free spaces through the protein network, forming interpenetrating networks of protein and polysaccharide. Although the WVP of the single-CMC film is lower than the other ones, its fragility is too great for it to be used as a coating or packaging. Therefore, it was concluded that CMC added to the SPI film could not promote significant changes in the WVP but contributed to improving the resistance of the SPI-based film and preserving its ductility, showing that SPI-CMC films can perform better than single films.