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- Pullulan–Apple Fiber Biocomposite Films: Optical, Mechanical, Barrier, Antioxidant and Antibacterial PropertiesPublication . Luís, Ângelo; Ramos, Ana; Domingues, Fernanda C.More than 150 million tons of synthetic plastics are produced worldwide from petrochemical-based materials, many of these plastics being used to produce single-use consumer products like food packaging. The main goal of this work was to research the production and characterization of pullulan–apple fiber biocomposite films as a new food packaging material. The optical, mechanical, and barrier properties of the developed biocomposite films were evaluated. Furthermore, the antioxidant and antibacterial activities of the biocomposite films were additionally studied. The results show that the Tensile Index and Elastic Modulus of the pullulan–apple fiber films were significantly higher (p-value < 0.05) when compared to the pullulan films. Regarding the water vapor permeability, no significant differences (p-value < 0.05) were observed in water vapor transmission rate (WVTR) when the apple fiber was incorporated into the biocomposite films. A significant increase (p-value < 0.05) of water contact angle in both sides of the films was observed when the apple fiber was incorporated into pullulan, indicating an increase in the hydrophobicity of the developed biocomposite films. It is worth noting the hydrophobicity of the (rough) upper side of the pullulan–apple fiber films, which present a water contact angle of 109.75°. It was possible to verify the microbial growth inhibition around the pullulan–apple fiber films for all the tested bacteria.
- Pullulan Films Containing Rockrose Essential Oil for Potential Food Packaging ApplicationsPublication . Luís, Ângelo; Ramos, Ana; Domingues, F.C.Active packaging is designed to control the development of decay- and disease-causing microorganisms and is emerging as a promising technology for extending shelf-life, maintaining food safety, reducing waste, and minimizing the risks for foodborne diseases. The goal of this work was to develop and characterize bioactive pullulan-based films, containing rockrose (Cistus ladanifer) essential oil. Among other abundant compounds (camphene, bornyl acetate and trans-pinocarveol), α-pinene was identified as the major compound of rockrose essential oil (39.25%). The essential oil presented stronger antibacterial activity against Gram-positive than against Gram-negative bacteria. The antioxidant results indicate the potential of the developed films to be used to package foods susceptible to oxidation and rancification, thus improving their shelf-life. Also, this study reflects the potential of rockrose essential oil, free or incorporated in pullulan, as a promising quorum sensing inhibitor, since it was able to interrupt intercellular communication, inhibiting violacein production. Electronic microscopy images showed the antibiofilm activity of the films with rockrose essential oil that were able to influence bacterial adhesion, which may be explained by the differences in the surface free energy of the films, as also determined.
- Pullulan-Tween 40 emulsified films containing geraniol: production and characterization as potential food packaging materialsPublication . Simões, Alexandra; Ramos, Ana; Domingues, F.C.; Luís, ÂngeloPetroleum-based plastics have been widely used as packaging materials because of their low-cost availability and good mechanical properties. However, the use of plastics has become restricted as they are highly resistant to biodegradation, causing environmental problems. This work aimed to produce and characterize emulsified pullulan films incorporating geraniol for application as food packaging materials with potential to substitute the conventional plastics. When geraniol was incorporated in the films, they showed antimicrobial activity against Enterococcus faecalis ATCC 29212 (inhibition zone diameter = 15.19 ± 0.66 mm) and Pseudomonas aeruginosa ATCC 27853 (inhibition zone diameter = 10.99 ± 1.82 mm). Furthermore, scanning electron microscopy showed the inhibition of Enterococcus faecalis ATCC 29212 biofilms when they were directly formed on the emulsified pullulan films incorporating geraniol. The produced films also demonstrated high transparency (> 90%) and hydrophilic surfaces (water contact angle < 90°). This work demonstrated the viability of using geraniol to produce pullulan active films as new food packaging materials.
- Design and Characterization of Bioactive Bilayer Films: Release Kinetics of Isopropyl PalmitatePublication . Luís, Ângelo; Gallardo, Eugenia; Ramos, Ana; Domingues, F.C.Active packaging incorporating antioxidants and antimicrobials is creating a niche in the market and becoming increasingly important. The main goal of this work was the design of bioactive bilayer films (zein/pullulan) incorporating licorice essential oil. The bilayer films were fully characterized in terms of their chemical, physical, barrier, antioxidant, and antimicrobial properties. Furthermore, the release kinetics of isopropyl palmitate, the major compound of the licorice essential oil, was evaluated by HPLC-DAD (high-performance liquid chromatography coupled to diode-array detector). Scanning Electron Microscopy (SEM) micrographs of cross-sections of the bilayer films clearly show the two layers of the films. Besides presenting the capacity to scavenge free radicals and to inhibit the lipid peroxidation, the developed bilayer films were also able to inhibit the growth of known foodborne pathogens (Enterococcus faecalis and Listeria monocytogenes). The release kinetics profile of isopropyl palmitate from bilayer films incorporating licorice essential oil demonstrated that in 50% ethanol at room temperature, the release was more effective, suggesting that the bilayer films will be more efficient if applied to package semi-fatty food.