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- Optimization of Whey Protein-Based Films Incorporating Foeniculum vulgare Mill: Essential OilPublication . Pedro, Salomé; Pereira, L.; Domingues, F.C.; Ramos, Ana; Luís, ÂngeloPetroleum-based plastics used in food packaging are not biodegradable. They accumulate in the environment in large amounts, causing a decrease in soil fertility, jeopardizing marine habitats, and causing serious problems to human health. Whey protein has been studied for applications in food packaging, either because of its abundant availability or because it confers transparency, flexibility, and good barrier properties to packaging materials. Taking advantage of whey protein to produce new food packaging materials is a clear example of the so-called circular economy. The present work focuses on optimizing the formulation of whey protein concentrate-based films to enhance their general mechanical properties applying the Box–Behnken experimental design. Foeniculum vulgare Mill. (fennel) essential oil (EO) was incorporated into the optimized films, which were then further characterized. The incorporation of fennel EO in the films leads to a significant increase (p < 0.05) in peak elongation (from 14.03 to 31.61%) and tensile index (from 0.40 to 0.50 N.m/g). The optimized whey protein films were yellowish and very transparent (>90%). The results of the bioactive activities of the optimized films showed their ability to be applied as active materials for food packaging to improve the shelf-life of food products and also to prevent foodborne diseases associated with the growth of pathogenic microorganisms.
- Production and Characterization of k-Carrageenan Films Incorporating Cymbopogon winterianus Essential Oil as New Food Packaging MaterialsPublication . Santos, Catarina; Ramos, Ana; Luís, Ângelo; Amaral, Maria EmíliaThe global production of synthetic plastics from petroleum-based raw ingredients exceeds 150 million metric tons. The environment is threatened by tons of plastic waste, thus endangering wildlife and the public’s health. These consequences increased the interest in biodegradable polymers as potential substitutes for traditional packaging materials. This study aimed to produce and characterize k-carrageenan films incorporating Cymbopogon winterianus essential oil, in which citronellal was determined to be the major compound (41.12%). This essential oil presented remarkable antioxidant activity, as measured through DPPH (IC50 = 0.06 ± 0.01%, v/v; AAI = 85.60 ± 13.42) and β-carotene bleaching (IC50 = 3.16 ± 0.48%, v/v) methods. The essential oil also showed antibacterial properties against Listeria monocytogenes LMG 16779 (diameter of inhibition zone = 31.67 ± 5.16 mm and MIC = 8 µL/mL), which were also observed when incorporated in the k-carrageenan films. Moreover, scanning electron microscopy showed the reduction of the biofilms of this bacterium, and even its inactivation, due to visible destruction and loss of integrity when the biofilms were created directly on the developed k-carrageenan films. This study also revealed the quorum sensing inhibition potential of Cymbopogon winterianus essential oil (diameter of violacein production inhibition = 10.93 ± 0.81 mm), where it could impede intercellular communication and, hence, lower violacein synthesis. The produced k-carrageenan films were transparent (>90%) and slightly hydrophobic (water contact angle > 90°). This work demonstrated the viability of using Cymbopogon winterianus essential oil to produce k-carrageenan bioactive films as new food packaging materials. Future work should focus on the scale-up production of these films.
- Production and characterization of pullulan/paper/zein laminates as active food packaging materialsPublication . Bilohan, Mariya; Ramos, Ana; Domingues, F.C.; Luís, ÂngeloPullulan/paper/zein laminates were developed as food packaging materials with active properties, taking advantage of the hydrophilic character of the pullulan where the rockrose essential was incorporated as a bioactive agent to be more easily released into the packaged food; paper improved the general mechanical properties of the developed materials; and the hydrophobic nature of zein improved the barrier properties of the developed materials. A cohesive microstructure without a clear boundary between the three layers was visualized by Scanning Electron Microscopy, which proves the good adhesion between them. It was found that the incorporation of rockrose essential oil significantly improves the ability of the laminates to inhibit lipid peroxidation. Thus, the potential for application of the developed laminates as new food packaging materials was confirmed, considering their ability to inhibit and/or prevent oxidation and lipid peroxidation and thereby increase the shelf life of the packaged food. The laminates also presented antimicrobial activity, specifically against Gram-positive strains. After 7 days of storage of fresh ham slices packaged with the developed laminates, it was observed that the texture parameters (shear force and shear energy) increased significantly in pullulan/paper/zein packages with and without the incorporation of rockrose essential oil.
- Production of Hydrophobic Zein-Based Films Bioinspired by The Lotus Leaf Surface: Characterization and Bioactive PropertiesPublication . Luís, Ângelo; Domingues, F.C.; Ramos, AnaHydrophobic zein-based functional films incorporating licorice essential oil were successfully developed as new alternative materials for food packaging. The lotus-leaf negative template was obtained using polydimethylsiloxane (PDMS). The complex surface patterns of the lotus leaves were transferred onto the surface of the zein-based films with high fidelity (positive replica), which validates the proposed proof-of-concept. The films were prepared by casting method and fully characterized by Scanning Electron Microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The grammage, thickness, contact angle, mechanical, optical and barrier properties of the films were measured, together with the evaluation of their biodegradability, antioxidant and antibacterial activities against common foodborne pathogens (Enterococcus faecalis and Listeria monocytogenes). The zein-based films with the incorporation of licorice essential oil presented the typical rugosities of the lotus leaf making the surfaces very hydrophobic (water contact angle of 112.50°). In addition to having antioxidant and antibacterial properties, the films also shown to be biodegradable, making them a strong alternative to the traditional plastics used in food packaging.
- 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.
- 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.
- 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.