Effect of the natural surfactant Yucca schidigera extract on the properties of biodegradable emulsified films produced from soy protein isolate and coconut oil

• The effect of coconut oil and Y. schidigera in biodegradable films was investigated.
• Emulsion-based films showed higher flexibility and lower water vapor permeability.
• The use of Y. schidigera extract and coconut oil changed the structure of the films.
• In general, the modifications proposed improved the properties of these films.

Protein films are known to have poor moisture barrier properties due to their hydrophilic nature, which can compromise the quality of packaged products. In this study, we present an alternative to overcome this problem by incorporating virgin coconut oil (VCO)—a hydrophobic component that presents good oxidative stability—into soy protein isolate (SPI) films. To emulsify the film-forming solution, the Yucca schidigera (YS) saponin was applied as natural surfactant. In order to understand the effect of VCO and YS into the SPI matrix, analyses of solubility, opacity, mechanical properties, water vapor permeability, morphological and structure properties were performed on the films. In general, all properties were influenced by the incorporation of VCO and/or surfactant, with exception of their solubility in water. Films containing VCO showed a plasticizing effect: increased flexibility and slight reduction in tensile strength. The water vapor permeability of the emulsion-based films was reduced in 35.4% when compared with the SPI film without VCO and YS. Morphological analyses indicated that the incorporation of VCO or Yucca extract caused notable changes in the structure of the SPI films, as also verified by Fourier transform infrared spectroscopy. Therefore, these data should help to better understand the role of lipids and surfactants in protein-based films for future industrial purposes.