The benefits of using biopolymers for the development of films and coatings are well known. The enrichment of these material properties through various natural additions has led to their applicability in various fields. Essential oils, which are well-known for their beneficial properties, are widely used as encapsulating agents in films based on biopolymers. In this study, we developed biopolymer-based films and tested their properties following the addition of 7.5% and 15% (w/v) essential oils of lemon, orange, grapefruit, cinnamon, clove, chamomile, ginger, eucalyptus or mint. The samples were tested immediately after development and after one year of storage in order to examine possible long-term property changes. All films showed reductions in mass, thickness and microstructure, as well as mechanical properties. The most considerable variations in physical properties were observed in the 7.5% lemon oil sample and the 15% grapefruit oil sample, with the largest reductions in mass (23.13%), thickness (from 109.67 µm to 81.67 µm) and density (from 0.75 g/cm3 to 0.43 g/cm3). However, the microstructure of the sample was considerably improved. Although the addition of lemon essential oil prevented the reduction in mass during the storage period, it favored the degradation of the microstructure and the loss of elasticity (from 16.7% to 1.51% for the sample with 7.5% lemon EO and from 18.28% to 1.91% for the sample with 15% lemon EO). Although the addition of essential oils of mint and ginger resulted in films with a more homogeneous microstructure, the increase in concentration favored the appearance of pores and modifications of color parameters. With the exception of films with added orange, cinnamon and clove EOs, the antioxidant capacity of the films decreased during storage. The most obvious variations were identified in the samples with lemon, mint and clove EOs. The most unstable samples were those with added ginger (95.01%), lemon (92%) and mint (90.22%).
The need to replace conventional, usually single-use, packaging materials, so important for the future of resources and of the environment, has propelled research towards the development of packaging-based on biopolymers, fully biodegradable and even edible. The current study furthers the research on development of such films and tests the modification of the properties of the previously developed biopolymeric material, by adding 10, respectively 20% w/v essential oils of lemon, grapefruit, orange, cinnamon, clove, mint, ginger, eucalypt, and chamomile. Films with a thickness between 53 and 102 µm were obtained, with a roughness ranging between 147 and 366 nm. Most films had a water activity index significantly below what is required for microorganism growth, as low as 0.27, while all essential oils induced microbial growth reduction or 100% inhibition. Tested for the evaluation of physical, optical, microbiological or solubility properties, all the films with the addition of essential oil in the composition showed improved properties compared to the control sample.
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