High-shear processing of surfactant-free corn starch films: impact of lemongrass essential oil on structural and antibacterial performance

This study evaluated the use of shear forces to incorporate different concentrations of lemongrass essential oil (LEO) into corn starch films, and assessed their thermal, chemical, mechanical, physical, and antibacterial properties. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of LEO were determined to assess its antibacterial activity. Films were produced via casting, using corn starch plasticized with glycerol and sorbitol. Corn starch films were prepared by incorporating LEO through a shear-assisted mixing process and the films were characterized for thickness, tensile strength and elongation at break, color parameters, water absorption, solubility, degradation in acid and saline medium, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and antibacterial properties. MIC and MBC tests confirmed LEO’s antibacterial efficacy, establishing concentrations of 1.6, 3.2, and 6.3 wt% in the dry starch base. Film thickness ranged from 0.290 to 0.310 mm, with no significant differences among formulations. Water absorption and solubility decreased with increasing LEO content. Compared to the film without LEO, the film containing 6.3 wt% LEO exhibited the lowest water absorption (69.05 ± 2.60%, a 23% reduction) and solubility (25.79 ± 0.81%, a 31% reduction), maintaining tensile strength (8.7 ± 0.5 MPa), elongation at break (106.3 ± 8.2%) and preserving the color parameters. TGA analysis revealed enhanced thermal stability for the film containing 6.3 wt% LEO (T5% = 127.9 °C; T10% = 186.7 °C) compared to the film without LEO (T5% = 108.8 °C; T10% = 168.1 °C). FTIR confirmed LEO incorporation, showing a characteristic band at 1672 cm⁻¹. Despite structural modifications, no measurable antibacterial activity was detected, likely due to limited LEO release, requiring further optimization.