Antimicrobial activity and physicochemical characterization of thermoplastic films based on bitter cassava starch, nanocellulose and rosemary essential oil

Extended shelf-life of many foods is a modern requirement that has been achieved by means of fossil-based plastic films despite their environmental issues. Recently, starch-based, fully biodegradable thermoplastics are gaining momentum as packaging material; however, if they are in contact with food, aspects such storage, water interaction and spoilage due to microorganisms must be considered. Essential oils are of great interest due to their antimicrobial action, so incorporating these compounds into natural polymers can promote a longer shelf life through active packaging. In this study, antibacterial activity, optical, mechanical and barrier properties of thermoplastic starch (TPS) films based on cassava starch (Manihot esculenta Crantz) and rosemary essential oil (REO) were studied. Furthermore, the effect of cellulose nanocrystals (CNC) on TPS properties were surveyed. Film mechanical properties and those related to the interaction with water, showed that the highest resistance and barrier properties corresponded to the TPS/CNC 15% film, while adding oil to the films increased morphological heterogeneity, contributed to reduce tensile strength, and increased water solubility and water vapor permeability. Likewise, TPS films containing rosemary oil showed enhanced antibacterial activity mostly against E. coli and S. aureus bacteria and A. niger fungus. Therefore, adding essential oils as natural additives favors using these biocomposites as functional packaging, and as potential replacements for single-use plastics.