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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.
- Development of a carboxymethyl xylan film containing licorice essential oil with antioxidant properties to inhibit the growth of foodborne pathogensPublication . Luís, Ângelo; Pereira, L.; Domingues, F.C.; Ramos, AnaAntioxidant and antibacterial edible films based on carboxymethyl xylan with licorice essential oil incorporated were successfully developed. The films were prepared by the casting method and characterized using FTIR. The grammage, thickness, contact angle, mechanical and optical properties of the films were measured, together with the evaluation of their antioxidant, antibacterial and anti-biofilm properties against common foodborne pathogens. The FTIR spectra of the films clearly show the successful incorporation of the essential oil. The antioxidant properties of the films linked to scavenging free radicals and lipid peroxidation inhibition were maintained even after a storage period at room temperature (20 days, 25 °C). Moreover, the capacity of these films to inhibit the growth of Enterococcus faecalis and Listeria monocytogenes was demonstrated. The results also suggest the anti-biofilm potential of films incorporated with licorice essential oil. Therefore, these biodegradable films can be used in active packages for food, improving the overall shelf life.
- 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.