Effects of Polyphenol-Rich Grape Seed and Green Tea Extracts on the Physicochemical Properties of 3D-Printed Edible Soy Protein Films

In this research, soy protein isolate (SPI) along with 0%, 1%, 3%, and 5% (w/w) of grape seed extract (GS) and green tea extract (GT) as natural antioxidants were used to develop edible active packaging materials using 3D printing technology. In addition, the effects of nozzle size (0.10, 0.25, and 0.33 mm) and pressure (0.020, 0.035, 0.048, and 0.062 MPa) on the 3D printing of the films were investigated. The printing accuracy was evaluated by comparing the areas of the 3D-printed films from their pictures to the area of the digital geometry. 3D printability of the films was considerably affected by the type and concentration of extracts due to the interactions between GS or GT and SPI, changing the SPI gel properties and, consequently, the printing performance. Compared to GT-loaded films, which showed a proper degree of shape preservation, the incorporation of 3 or 5% GS resulted in the deformation of the films during 3D printing. Soy protein edible films loaded with 1-3% (w/w) GS or GT were 3D-printed with high accuracy (>98%) at a printing pressure of 0.062 MPa and nozzle diameter of 0.25 mm. When higher concentrations (5%, w/w) of GS or GT were added, the 3D-printed films became thicker and less transparent. The tensile strength of the films was increased by the incorporation of extracts. The tensile strength of the GS-loaded films was higher than that of the GT-loaded films. Moreover, the addition of GS and GT reduced the water vapor permeability (WVP) of SPI by 61% and 56%, respectively. Overall, the proposed 3D printing approach can provide flexibility in generating edible films in different geometries and properties for on-line packaging applications.