Production of active food packaging film based on gelatin/aloe vera gel containing rosemary essential oil

Introduction: Study on modern biodegradable packaging materials has attracted the attention of researchers, due to increasing concerns about food safety and environmental issues related to waste generated by non-degradable plastic packaging. One of these modern packaging technologies is active packaging, which offers a sustainable and environmentally friendly way to improve the shelf life of food. In the food packaging industry, gelatin is one of the frequently used biopolymers. In addition, gelatin has been used in the fields of cosmetics, food industry, tissue engineering, and pharmaceuticals due to properties such as good biocompatibility, unique functional properties, abundant extraction sources, and biodegradability. However, pure gelatin film exhibits low mechanical, antioxidant and antimicrobial properties, limiting its practical use as active packaging. Therefore, active packaging films and coatings are usually combined with various biopolymers, natural extracts, nanofillers to improve their properties, and enhance food safety. Rosemary is an evergreen plant, belonging to the Lamiaceae family. Its extract or essential oil has antioxidant, anti-inflammatory, anti-tumor, anti-obesity and anti-diabetic properties. Rosemary essential oil also has antibacterial and antifungal activity. These health benefits of rosemary are due to the phenolic substances in its composition, including carnosol, carnosic acid and rosemanol. Many studies have included rosemary essential oil in food packaging to prevent food spoilage. Aloe vera is a xerophytic plant belonging to the Aloaceae family that grows in tropical regions of the world. Several researchers have reported that aloe vera has a variety of biological activities, including anti-inflammatory, antioxidant, and immunomodulatory. In the past decades, the use of aloe vera gel in edible films has received attention due to its effectiveness in increasing the shelf life of various perishable foods. The antioxidant and antimicrobial potential of aloe vera gels make them an excellent example of active packaging.
Material and methods: In this study, rosemary essential oil was extracted using a Clevenger apparatus. Also, aloe vera gel was extracted from the aloe vera plant. Then, gelatin-based films were produced using the casting method. Afterward, the produced film thickness was measured using a digital micrometer. Also, the film samples were placed in glass vials containing calcium chloride, to measure the water vapor permeability. The film surface morphology analyzed using a scanning electron microscope. Also, an X-ray diffractometer was used in the 2θ = 5-75 to check the crystal structure. Furthermore, Fourier transform infrared spectroscopy was used to check the chemical structure of the films. Moreover, disc diffusion method was used to analyze the antimicrobial properties of the films.
Results: The results showed that the thickness of the film containing aloe vera gel and rosemary essential oil was higher than the pure gelatin film. Also, water solubility and moisture content of the films were significantly reduced by adding aloe vera gel and rosemary essential oil. The pure gelatin film had a tensile strength of 20.74 MPa, flexibility of 21.42 % and Young's modulus was 165.14 MPa. The addition of rosemary essential oil increased the tensile strength of the film to 33.61 MPa. However, Young's modulus and flexibility of the film did not show a significant change (p < 0.05). Also, the addition of aloe vera gel increased the flexibility (30.24 %) of the film and decreased the tensile strength (17.92 MPa) and Young's modulus (44.18 MPa). In addition, the pure gelatin film had a uniform and smooth surface, which is the basic morphology of gelatin films. Also, the surface of the film maintained its uniformity and smoothness with the addition of aloe vera gel, which can indicate the complete dissolution of aloe vera gel as a result of its hydrophilic nature. Furthermore, the addition of rosemary essential oil formed a very homogeneous and uniform surface, which can be caused by the placement of rosemary essential oil inside the continuous polymer network of gelatin. X-ray diffraction results showed that at 2θ ~19°, all films had a broad peak, which indicates the semi-crystalline structure of gelatin and caused. However, the addition of rosemary essential oil and aloe vera gel did not cause a significant change in the crystalline structure of gelatin-based films, which could be due to the amorphous structure of aloe vera gel and rosemary essential oil. Also, the pure gelatin film had no antioxidant activity. However, the antioxidant activity of the film increased to 15.60% with the addition of aloe vera gel. Similarly, adding rosemary essential oil to the film caused 11.71% antioxidant activity of the film. In addition, pure gelatin and gelatin/aloe vera film did not have antibacterial activity. However, the addition of rosemary essential oil to the gelatin-based film caused significant antibacterial activity of the film, which is due to the presence of diterpene compounds such as carnosic acid, carnosol, rosmanol, isorosmanol, and rosmarinic acid in the structure of rosemary.
Conclusion: Briefly, gelatin active film containing rosemary essential oil and aloe vera gel was prepared using the casting method. Investigation of the optical, mechanical, barrier, antioxidant, and antimicrobial properties of the film samples showed that gelatin/rosemary essential oil/aloe vera gel film had the lowest water solubility and moisture content, promising mechanical, light barrier, and antioxidant properties. Also, this film had suitable antibacterial against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative) bacteria, which indicates its significant potential for active food packaging.