Chemist uses bay leaf extracts to create biodegradable films
A chemist from RUDN University synthesized biodegradable films with the addition of bay leaf essential oils. Together with his Spanish colleagues, he modified the production of packaging material based on carboxymethyl cellulose. As it turned out, with the extract, either the films will have new properties or existing properties will be improved, depending on the concentration: solubility, bactericidal effect, fineness, etc. The article was published in the journal Materials.
Products need packaging that protects them from the environment. Usually, plastics are used for that purpose, but they are a danger to nature. That is why chemists are now looking for a biodegradable alternative. New materials should protect products from UV radiation, prevent the passage of moisture, inhibit the growth of pathogenic microorganisms, and be resistant to mechanical stress. Bay leaf oils are known for their high polyphenol content, which has antioxidant and antimicrobial effects. Therefore, they can be used to improve the properties of package materials.
Rafael Luque and his colleagues obtained biodegradable films with the "solvent casting" method using carboxymethyl cellulose. Essential oils of the laurel tree were added in the process of synthesis. Substances were extracted with the Soxhlet method using ethanol or methanol as an organic solvent. The chemists obtained films with extract concentrations ranging from 1% to 30%, and then evaluated their properties.
Water content, solubility, extensibility, and rupture resistance of the obtained films were studied.
Essential oils extracted with ethanol had greater antioxidant ability and higher phenol content than essential oils extracted with methanol (74.73 ± 4.71% versus 62.13 ± 0.71% and 83.41 ± 4.19 versus 48.34 ± 3.51, respectively). The thinnest material turned out to be the one obtained with the addition of 30% of essential oils extracted with methanol. The films produced with the addition of 20% ethanol extract of bay leaf contained the least moisture. All of them showed approximately the same solubility, but the most soluble was the material with the addition of 30% ethanol extract. The best at moisture permeability was the film in which 10% methanol extract was present.
In tests for stretch and rupture, films containing 1% extracts performed the best. The most transparent were materials containing 1% essential oils, but the ability to absorb UV was the greatest in materials with 30% essential oils. The highest antioxidant activity was observed in films with the addition of 30% ethanol extract, but the total content of phenolic compounds in films with the addition of 30% methanol and ethanol extracts turned out to be comparable.
The experiments have shown a positive correlation between the concentration of added essential oils of bay leaves and the thickness of films and their capacity to dissolve in water. Films with the addition of a 15% ethanol extract and a 30% methanol extract pass half as much moisture as a conventional carboxymethyl cellulose film. The material obtained by adding a 15% extract showed bactericidal properties and good capacity to absorb UV radiation. But in order to effectively use these films in industry, a plasticizer needs to be added, which will improve the films' mechanical properties. In further research, the extraction process of bay leaf essential oils for biodegradable films is going to be optimized.
The optical properties of the films were studied using spectrophotometry, and the antioxidant capacity of the material was evaluated by its ability to restore ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)). The antimicrobial properties of the films were evaluated by incubating E. coli and C. glabrata in the presence of the studied fragments.
To determine the initial composition of the extracts, the scientists used gas chromatography; the total content of phenolic substances was determined using the Folin–Ciocalteu method. Antioxidant properties were evaluated using essential oils and substances taken for comparison (eucalyptol, linalool, and eugenol).
"There was no residual methanol in the film, being very pure on the extract. The ability of the extracts was tested separately without the films, being excellent. The film 30% extract was indeed optimum to inhibit bacterial growth", Luque said.
More information:
Rincón et al. Effect of Bay Leaves Essential Oil Concentration on the Properties of Biodegradable Carboxymethyl Cellulose-Based Edible Films, Materials (2019). DOI: 10.3390/ma12152356
Provided by RUDN University