Essential oils as additives in biodegradable films and coatings for active food packaging

Petroleum derivate plastics represent a serious environmental problem, which is why alternative sustainable solutions must be found. To this aim, recent research has focused on the development of edible/biodegradable packaging for food products. The implementation of this novel packaging requires analyzing thoroughly the effect of the ingredients used on the most relevant properties of the material. Essential oils represent an interesting ingredient for biodegradable food packaging, mainly due to their natural origin and their functional (antioxidant/antimicrobial) properties, allowing for obtaining active materials aiming to extend shelf-life and add value to the product. However, their inclusion in edible/biodegradable films for food packaging may imply some impact on several properties of the system (such as optical, tensile…), affecting in turn the consumer acceptability. Before the increasing research on biodegradable materials for food packaging, and the growing interest on natural food additives, this paper aims to review the latest findings on how essential oils impact the most relevant properties of edible films and coatings, namely microstructural, physical (tensile, barrier, optical), antioxidant and antimicrobial. Essential oil incorporation affects the continuity of the polymer matrix, leading to physical changes depending on the specific polymer-oil components interactions. Generally, the film structure is weakened by the oil addition, whereas the water barrier properties are improved and the transparency is reduced. Essential oils may provide the films with antioxidant and/or antimicrobial properties. The oil composition and the specific interactions with the polymer determine its effectiveness as an active ingredient.