Characterization of cassava starch/soy protein isolate blends obtained by extrusion and thermocompression

Abstract

To develop biodegradable food packaging, different biopolymer blend ratios of cassava starch (S) and soy protein isolate (P) (S100, S85P15, S70P30, S55P45, S40P60, and P100) were prepared by the extrusion method and then characterized. Before their application in foods, these blends must be characterized to enable the selection of the optimum materials for different packaging applications. For this purpose, the thermal and structural properties of the blends and possible interactions between the polymers were analyzed by thermogravimetric analysis (TG), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy. The moisture and oil resistance (surface energy, water vapor permeability (WVP), moisture content and solubility, and oil permeability), mechanical properties (tensile and puncture strength), and transparency of the blends were also investigated. The addition of protein resulted in crosslinking between the starch and protein chains and increased the crystallinity, as observed by FTIR, XRD, and DMA. Consequently, the stiffness of S40P60 increased, presenting a 120 % higher elastic modulus, and the WVP decreased 25 % compared to S100, likely due to the crosslinking of the polymer chains promoted by the addition of protein. In contrast, the S70P30 blend had greater hydrophilicity, leading to 68 % increase in moisture content and WVP, respectively. The S40P60 blend presented 22 % higher water solubility than the other blends. The S85P15 blend exhibited higher dispersive energy ability, and consequently, higher permeability to oil. P100 was 19 % less transparent than the other samples. Concerning the studied blends, S40P60 presented a low water vapor and oil permeability and low dispersive energy, while also presenting low transparency. Therefore, the use of this blend should be considered for packaging for foods with high lipid contents.