Antimicrobial Poly(lactic acid)-Based Nanofibres Developed by Solution Blow Spinning.

The present study reports on the development of hybrid poly(lactic acid) (PLA) fibres loaded with highly crystalline bacterial cellulose nanowhiskers (BCNW) by the novel solution blow spinning method. Furthermore, fibres with antimicrobial properties were generated by incorporating carvacrol and THC as antimicrobial agents and the biocide effect against Listeria monocytogenes was studied. Initially, PLA blow spun fibres containing BCNW were optimized in terms of morphology and thermal properties. The addition of BCNW was seen to significantly increase the viscosity and surface tension of solutions, restricting the capacity to form fibres for concentrations greater than 30 wt.-% BCNW. 15 wt.-% BCNW was selected as the optimum nanofiller loading as it led to the most uniform fibres morphology, with BCNW homogeneously distributed along the fibres' axis. Subsequently, carvacrol and THC were incorporated into the fibres to confer them with antimicrobial properties, although the hydrophobic PLA matrix did not provide an efficient release of the antimicrobials. Thus, hydrophilic substances were added in order to trigger the antimicrobials release through water sorption mechanisms. The addition of the BCNW filler was not seen to significantly increase the antimicrobial capacity of the fibres by itself and, hence, gelatin was added to help promoting further the hydrophylicity and biocide performance of the fibres. Nevertheless, for the more hydrophilic THC, the biocide capacity of the fibres with gelatin was accentuated further by the presence of the BCNW.

Order matters: Methods for extracting cellulose from rice straw by coupling alkaline, ozone and enzymatic treatments.

Rice straw is a widely produced residue that can be converted into value-added products. This work aimed at using greener processes combining mild alkali (A), ozone (O) and enzymatic (engineered xylanase) (E) treatments to extract cellulose and other value-added compounds from rice straw and to evaluate the effects of the order of the treatments. Solid (S) and liquid (L) fractions from the process were collected for physicochemical characterization. AOE treatment showed the best capacity to extract high purity cellulose and other valuable compounds. The lignin content was significantly decreased independently of the order of the treatments and, its content in the extract obtained after the AOE process was lower than the one obtained after the OAE process. Moreover, thermal stability of the samples increased after the enzymatic process, being higher in SAOE. The alkaline treatment increased the hemicellulose and polyphenol content (antioxidant activity) in the liquid fractions (LA and LOA). In contrast, the ozonized liquid fractions had lower polyphenol content. Therefore, alkali was fundamental in the process. In conclusion, the AOE strategy could be a more environmentally friendly method for extracting cellulose and other valuable compounds, which could be used to develop active materials in the future.

Comparative toxicity of conventional versus compostable plastic consumer products: An in-vitro assessment.

This study investigates the toxicity of methanolic extracts obtained from compostable plastics (BPs) and conventional plastics (both virgin and recycled). Additionally, it explores the potential influence of plastic photodegradation and composting on toxic responses using a battery of in vitro assays conducted in PLHC-1 cells. The extracts of BPs, but not those of conventional plastics, induced a significant decrease in cell viability (<70%) in PLHC-1 cells after 24 h of exposure. Toxicity was enhanced by either photodegradation or composting of BPs. Extracts of conventional plastics, and particularly those of recycled plastics, induced 7-ethoxyresorufin-O-deethylase (EROD) activity and micronucleus formation in exposed cells, indicating the presence of significant amounts of CYP1A inducers and genotoxic compounds in the extracts, which was enhanced by photodegradation. These findings highlight the importance of investigating the effects of degradation mechanisms such as sunlight and composting on the toxicity of BPs. It is also crucial to investigate the composition of newly developed formulations for BPs, as they may be more harmful than conventional ones.

Optimization of the dispersion of unmodified bacterial cellulose nanowhiskers into polylactide via melt compounding to significantly enhance barrier and mechanical properties.

In the present study, property-enhanced polylactide (PLA) nanocomposites containing bacterial cellulose nanowhiskers (BCNW) were prepared by melt compounding. With the aim of improving the nanocrystals' dispersion in the final melt processed nanocomposites, these were preincorporated either into PLA nanostructured fibers by electrospinning or into an ethylene vinyl-alcohol copolymer (EVOH) by solution precipitation. An optimized dispersion of the nanofiller in the nanocomposites produced by applying these preincorporation methods, when compared to the direct melt mixing of the freeze-dried nanowhiskers with the polymeric matrix, was confirmed by morphological studies. Enhanced dispersion of BCNW was critical for enhancing the barrier and mechanical properties of the nanocomposites. Thus, for concentrations around the percolation threshold, that is, 2-3 wt % BCNW, nanocomposites produced by the electrospinning preincorporation method showed increased elastic modulus and tensile strength, preserving the ductility of the pure PLA. Moreover, in the optimized nanocomposites the water permeability of PLA was reduced by 43% and the oxygen barrier also decreased to a significant extent. This paper provides a successful route to solve the long-standing issue related to the dispersion of highly polar unmodified cellulose nanowhiskers into PLA via the industrially meaningful melt compounding processing.

Multifunctional cellulosic aerogels from Posidonia oceanica waste biomass with antioxidant properties for meat preservation.

Posidonia oceanica waste biomass has been valorized to develop bioactive multifunctional cellulosic aerogels (HCAG) by simpler and greener protocols. Hydrophobization of cellulosic aerogels was achieved through PLA coating, while bioactivity was imparted by the incorporation of hydrophilic (E2) and hydrophobic extracts (E3) produced from the same biomass. The incorporation of extracts led to denser aerogels, with less porous structures. These aerogels showed outstanding water and oil sorption capacities (1500-1900%), being able to release the adsorbed liquid almost completely after 7 days. Interestingly, all the aerogels showed a positive inhibition effect (23-91%) on the ß-carotene bleaching assay. Moreover, the aerogels loaded with extracts, especially when combining E2 and E3, were able to reduce the oxidation of lipids and oxymyoglobin in red meat after 10 days of storage. This evidences the potential of these multifunctional aerogels as bioactive adsorbing pads to preserve the quality of fresh packaged foods.

Encapsulation of Plant-derived Bioactive Ingredients through Electrospraying for Nutraceuticals and Functional Foods Applications.

The electrospraying technique, which consists of electrohydrodynamic atomization of polymeric fluids, can be used to generate dry nano- and microparticles by subjecting a polymer solution, suspension or melt to a high voltage (typically in the range of 7-20 kV) electric field. This potential can be exploited for developing nano- and microencapsulation structures under mild temperature conditions. Thus, it constitutes a promising alternative to conventional microencapsulation techniques for sensitive ingredients, like most plant-derived bioactive compounds, especially for their application in the food sector. Given the importance of plants as one of the major sources of dietary bioactive compounds, significant attention has been recently paid to research the encapsulation of phytochemicals through novel techniques such as electrospraying, aiming to provide new tools for the development of innovative functional food products and nutraceuticals. In this review, the latest advances in the application of electrospraying for nano- and microencapsulation of phytochemicals are discussed, with a focus on their potential use in the food sector.

Improved performance of less purified cellulosic films obtained from agar waste biomass.

The residues generated after the extraction of agar from Gelidium sesquipedale by means of a hot-water treatment, with (NaOH+HW residue) and without (HW residue) an alkali pre-treatment have been valorized to produce high performance cellulosic films. Both residues were mainly composed of structural carbohydrates (in particular, agar), ashes and lipids. The residual agar could only be completely removed by applying a two-step process based on bleaching and alkaline treatments. The application of the alkaline pre-treatment for the extraction of agar did not significantly affect the properties of the films produced from the extracted fractions, hence making the HW residue more sustainable and economically viable. The agar remaining in the less purified fractions had a positive effect on the performance of the films, improving their transparency, mechanical properties and water vapour barrier, outperforming benchmark biopolymers; in addition, these materials presented antioxidant capacity inhibiting the degradation of ß-carotene.

Valorisation of vine shoots for the development of cellulose-based biocomposite films with improved performance and bioactivity.

This work reports on the valorization of Tempranillo vine shoots for the development of bio-based packaging materials. Cellulose (F3) and nanocellulose (NANO F3) were produced by the conventional method, while less purified cellulosic fractions (F2A) and nanocrystals (NANO F2A) were extracted by simplified protocols (omitting Soxhlet and alkaline treatments) to reduce production costs and environmental impact and evaluate the potential added functionalities of these less purified materials. Although most of the hemicelluloses in F2A were digested upon acid hydrolysis, a small fraction remained in NANO F2A. On the other hand, the presence of a minor xylan fraction in F3 limited the access of sulphuric acid towards the cellulose microfibrils, hindering hydrolysis and producing heterogeneous fibrillar structures in NANO F3. The obtained materials were used to produce cellulosic films, as well as blends with agar, and their performance properties were evaluated. Overall, NANO F2A films showed the best compromise between performance and sustainability and presented additional antioxidant capacity. The properties of the films could be adjusted by the incorporation of agar, improving their ductility and water permeability.

Encapsulation of living bifidobacteria in ultrathin PVOH electrospun fibers.

This study shows the application of the electrospinning technique as a viable method for the encapsulation and stabilization of bifidobacterial strains. Poly(vinyl alcohol) (PVOH) was used as the encapsulating material because it is generally recognized as safe (GRAS), has a high oxygen barrier when dry, and is water soluble, hence allowing easy recovery of the bacteria for viability testing. A coaxial setup was used for encapsulation, and the so-obtained electrospun fibers had a mean diameter of ca. 150 nm. Incorporation of B. animalis Bb12 led to a decrease in melting point and crystallinity of the PVOH fibers and to an increase in the polymer glass transition temperature. The viability tests, carried out at three different temperatures (room temperature and 4 and -20 degrees C) showed that B. animalis Bb12 encapsulated within the electrospun PVOH fibers remained viable for 40 days at room temperature and for 130 days at refrigeration temperature, whereas a significant viability decrease was observed in both cases when bacteria were not encapsulated (p = 0.015 and p = 0.002, respectively).

High-performance starch biocomposites with celullose from waste biomass: Film properties and retrogradation behaviour.

In this work, the effects of relative humidity (RH) pre-conditioning (53% vs. 85% RH) and incorporation of cellulose fillers (from Posidonia waste biomass) on the properties and retrogradation of melt compounded starch biocomposites were investigated. Pre-conditioning at 85% RH promoted starch gelatinization during processing, leading to more amorphous materials with reduced stiffness but better barrier properties. Furthermore, these films were less stable upon storage due to greater starch retrogradation. Cellulose incorporation improved significantly the mechanical and water barrier performance, especially in the films pre-conditioned at 85% RH due to enhanced filler dispersion. Although incomplete gelatinization of the starch pre-conditioned at 53% RH led to films with bigger cellulose aggregates, their mechanical and water barrier properties were better, outperforming starch-cellulose biocomposites typically reported in the literature. Moreover, the presence of cellulose limited the degree of starch retrogradation upon storage, highlighting the potential of Posidonia biomass as a cheap source of high-performance fillers.

Potential of lignocellulosic fractions from Posidonia oceanica to improve barrier and mechanical properties of bio-based packaging materials.

This work reports on the valorization of residues from Posidonia oceanica leaves for the purpose of obtaining lignocellulosic fractions of interest for the development of bio-based materials for food packaging. The lignocellulosic fractions were characterized, thereby confirming the purification of cellulose and showing increases in crystallinity and thermal stability after the consecutive extraction steps. Subsequently, pure lignocellulosic films were obtained and characterized and the pure cellulose film showed the best properties in terms of mechanical performance and water vapor permeability. Finally, composite starch films containing lignocellulosic fractions were developed by melt compounding and characterized. Although the film containing the pure cellulose additive showed the optimum improvement in terms of mechanical properties (with an increase of 85% in the elastic modulus and 38% in the tensile strength), similar water vapor permeability reduction (~40%) was achieved with the least purified fractions, explained by their effect on starch gelatinization, as evidenced by SAXS/WAXS.

Development of enzymatically-active bacterial cellulose membranes through stable immobilization of an engineered ß-galactosidase.

Enzymatically-active bacterial cellulose (BC) was prepared by non-covalent immobilization of a hybrid enzyme composed by a ß-galactosidase from Thermotoga maritima (TmLac) and a carbohydrate binding module (CBM2) from Pyrococcus furiosus. TmLac-CBM2 protein was bound to BC, with higher affinity at pH 6.5 than at pH 8.5 and with high specificity compared to the non-engineered enzyme. Both hydrated (HBC) and freeze-dried (DBC) bacterial cellulose showed equivalent enzyme binding efficiencies. Initial reaction rate of HBC-bound enzyme was higher than DBC-bound and both of them were lower than the free enzyme. However, enzyme performance was similar in all three cases for the hydrolysis of 5% lactose to a high extent. Reuse of the immobilized enzyme was limited by the stability of the ß-galactosidase module, whereas the CBM2 module provided stable attachment of the hybrid enzyme to the BC support, after long incubation periods (3 h) at 75 °C.

Self-assembled gelatin-ι-carrageenan encapsulation structures for intestinal-targeted release applications.

In this work, natural biopolymeric encapsulation structures were developed through the self-assembly of gelatin and ι-carrageenan in aqueous solutions. The interactions of this binary system and of a ternary system containing a polyphenol-rich extract were deeply explored for the development of intestinal delivery systems. The processing of the structures (extrusion vs. freeze-drying) greatly influenced release properties, explained by the specific interactions between gelatin and polyphenols, thus allowing for tuning the processing conditions depending on the desired target application. Release was further controlled by incorporating a divalent salt, giving raise to extract-loaded ι-carrageenan/gelatin capsules with adequate release profiles for intestinal targeted delivery. These results demonstrate the potential of exploiting biopolymer interactions for designing bioactive delivery systems using environmentally friendly processes which do not involve the use of toxic or harsh solvents or cross-linkers.

Microencapsulation structures based on protein-coated liposomes obtained through electrospraying for the stabilization and improved bioaccessibility of curcumin.

Novel food-grade hybrid encapsulation structures based on the entrapment of phosphatidylcholine liposomes, within a WPC matrix through electrospraying, were developed and used as delivery vehicles for curcumin. The loading capacity and encapsulation efficiency of the proposed system was studied, and the suitability of the approach to stabilize curcumin and increase its bioaccessibility was assessed. Results showed that the maximum loading capacity of the liposomes was around 1.5% of curcumin, although the loading capacity of the hybrid microencapsulation structures increased with the curcumin content by incorporation of curcumin microcrystals upon electrospraying. Microencapsulation of curcumin within the proposed hybrid structures significantly increased its bioaccessibility (∼1.7-fold) compared to the free compound, and could successfully stabilize it against degradation in PBS (pH=7.4). The proposed approach thus proved to be a promising alternative to produce powder-like functional ingredients.

Tailoring barrier properties of thermoplastic corn starch-based films (TPCS) by means of a multilayer design.

This work compares the effect of adding different biopolyester electrospun coatings made of polycaprolactone (PCL), polylactic acid (PLA) and polyhydroxybutyrate (PHB) on oxygen and water vapour barrier properties of a thermoplastic corn starch (TPCS) film. The morphology of the developed multilayer structures was also examined by Scanning Electron Microscopy (SEM). Results showed a positive linear relationship between the amount of the electrospun coatings deposited onto both sides of the TPCS film and the thickness of the coating. Interestingly, the addition of electrospun biopolyester coatings led to an exponential oxygen and water vapour permeability drop as the amount of the electrospun coating increased. This study demonstrated the versatility of the technology here proposed to tailor the barrier properties of food packaging materials according to the final intended use.

Hybrid encapsulation structures based on ß-carotene-loaded nanoliposomes within electrospun fibers.

Hybrid encapsulation structures based on ß-carotene-loaded nanoliposomes incorporated within the polymeric ultrathin fibers produced through electrospinning were developed to improve the photostability of the antioxidant. These novel materials were intended to incorporate ß-carotene into water-based food formulations, overcoming the existing limitations associated with its hydrophobic character. Initially, both empty and antioxidant-loaded nanoliposomes were developed and incorporated into polyvinyl alcohol (PVOH) and polyethylene oxide (PEO) solutions. The changes in the solution properties were evaluated to determine their effects on the electrospinning processing. The mixed polymer solutions were subsequently electrospun to produce hybrid nanoliposome-loaded ultrathin fibers. FTIR analysis confirmed the presence of phospholipid molecules inside the electrospun fibers. These ultrathin fibers were evaluated regarding their morphology, diameter, internal ß-carotene distribution and stability against UV irradiation. Liposomal release studies from the electrospun fibers were also undertaken, confirming the presence of the liposomal structures after dissolving the electrospun fibers in water.

Characterization of polyhydroxyalkanoates synthesized from microbial mixed cultures and of their nanobiocomposites with bacterial cellulose nanowhiskers.

The present work reports on the production and characterization of polyhydroxyalkanoates (PHAs) with different valerate contents, which were synthesized from microbial mixed cultures, and the subsequent development of nanocomposites incorporating bacterial cellulose nanowhiskers (BCNW) via solution casting processing. The characterization of the pure biopolyesters showed that the properties of PHAs may be strongly modified by varying the valerate ratio in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer, as expected. Increasing the valerate content was seen to greatly decrease the melting temperature and enthalpy of the material, as well as its rigidity and stiffness, resulting in a more ductile behaviour. Additionally, the higher valerate PHA displayed higher permeability to water and oxygen and higher moisture sensitivity. Subsequently, BCNW were incorporated into both PHA grades, achieving a high level of dispersion for a 1 wt.-% loading, whereas some agglomeration took place for 3 wt.-% BCNW. As evidenced by DSC analyses, BCNW presented a nucleating effect on the PHA matrices. BCNW also increased the thermal stability of the polymeric matrices when properly dispersed due to strong matrix-filler interactions. Barrier properties were seen to depend on relative humidity and improved at low nanofiller loadings and low relative humidity.

High-barrier coated bacterial cellulose nanowhiskers films with reduced moisture sensitivity.

This study reports on the development and characterization of bacterial cellulose (BCNW) films coated with hydrophobic layers, presenting enhanced barrier properties. Pure BCNW films showed good transparency and thermal stability, high rigidity and extremely low oxygen permeability at 0%RH. The dramatic increase in oxygen permeability at 80%RH, due to the hydrophilic character of BCNW, was counteracted through coating the films with annealed PLA electrospun nanostructured fibres or hydrophobic silanes. The use of electrospinning was crucial to attain a good adhesion between the hydrophilic BCNW and the hydrophobic PLA layer. After electrospinning, the fibres were homogenised by annealing, thus obtaining a uniform and continuous coating. Coated systems showed a hydrophobic surface and protected the BCNW from moisture, thus reducing ca. 70% the water permeability and up to 97% the oxygen permeability at 80%RH. Furthermore, this novel approach was seen to protect BCNW films from moisture more efficiently than coating with hydrophobic silanes.

Gliadins polymerized with cysteine: effects on the physical and water barrier properties of derived films.

To study the effects of disulfide bonds on certain functional properties of films made from the wheat gluten proteins gliadin and glutenin, cysteine was used to promote the formation of interchain disulfide bridges between gliadins in 70% ethanolic solution. Disulfide-mediated polymerization of gliadins was confirmed by means of SDS-PAGE analysis. After chemical treatment of gliadins, films were solution cast and the effects of both glycerol (used as a plasticizer) and relative humidity were studied on water vapor permeability, moisture sorption isotherms at 23 degrees C, and the optical properties of the films. The results were compared with those obtained from analogous films made from untreated glutenin macromolecules. Cysteine-mediated polymerization of gliadins improved the water vapor resistance of films achieving values close to those obtained for glutenin films. Development of intra- and interchain disulfide bonds did not change the moisture sorption capacity of the films but transparency was slightly diminished.