Developing Active Modified Starch-Based Films Incorporated with Ultrasound-Assisted Muña (Minthostachys mollis) Essential Oil Nanoemulsions

In this study, an I-optimal design was used to select an optimal muña essential oil nanoemulsion (MEO-NE) for application in active starch-based films. Four independent variables were used to optimize the process: emulsifier concentration (X₁) (% <i>w</i>/<i>w</i>), sonication time (X₂) (min), essential oil concentration (X₃) (% <i>w</i>/<i>w</i>), and emulsifier type (X₄) (Tween 80 or sapote gum). Results revealed that MEO-NE containing 5.24% of MEO, 6% Tween^® 80, and 9 min of ultrasound treatment exhibited a small droplet size (Y₁) (48.6 nm), moderate ζ-potential (Y₂) (-15 mV), and DPPH inhibition (Y₃) (95.6%). Starch-based films were incorporated with optimized MEO-NE at 5% (F₁) and 10% (F₂) and compared with control films (F₀). F₁ and F₂ exhibited lower moisture content, water solubility, and water vapor permeability than F₀; however, their contact angles were higher. The addition of MEO-NE into the polymeric matrix increased the stiffness of F₁ and F₂; however, the elongation at yield was slightly lower than that of F₀, resulting in less stretchable composite films. All films were disintegrated by more than 90% after 5 days of burial under composting conditions. The incorporation of MEO-NE into composite films significantly enhanced their properties, suggesting their potential use as eco-friendly packaging.