State of the Art Membrane Science and Technology in the Iberian Peninsula 2021-2022.

This Special Issue of the journal Membranes arises from the need to highlight the developments in the field of membrane research and membrane processes that have been emerging in recent years by researchers and research groups based in the Iberian Peninsula [...].

Current Applications of Bionanocomposites in Food Processing and Packaging.

Nanotechnology advances are rapidly spreading through the food science field; however, their major application has been focused on the development of novel packaging materials reinforced with nanoparticles. Bionanocomposites are formed with a bio-based polymeric material incorporated with components at a nanoscale size. These bionanocomposites can also be applied to preparing an encapsulation system aimed at the controlled release of active compounds, which is more related to the development of novel ingredients in the food science and technology field. The fast development of this knowledge is driven by consumer demand for more natural and environmentally friendly products, which explains the preference for biodegradable materials and additives obtained from natural sources. In this review, the latest developments of bionanocomposites for food processing (encapsulation technology) and food packaging applications are gathered.

Opuntia spp.: An Overview of the Bioactive Profile and Food Applications of This Versatile Crop Adapted to Arid Lands.

Opuntia spp. are crops well adapted to adverse environments and have great economic potential. Their constituents, including fruits, cladodes, and flowers, have a high nutritional value and are rich in value-added compounds. Cladodes have an appreciable content in dietary fiber, as well as bioactive compounds such as kaempferol, quercetin, and isorhamnetin. Fruits are a major source of bioactive compounds such as phenolic acids and vitamin C. The seeds are mainly composed of unsaturated fatty acids and vitamin E. The flowers are also rich in phenolic compounds. Therefore, in addition to their traditional uses, the different plant fractions can be processed to meet multiple applications in the food industry. Several bakery products have been developed with the incorporation of cladode flour. Pectin and mucilage obtained from cladodes can act as edible films and coatings. Fruits, fruit extracts, and fruit by-products have been mixed into food products, increasing their antioxidant capacity and extending their shelf life. Betalains, obtained from fruits, can be used as food colorants and demonstrate promising applications as a sensor in food packaging. This work reviews the most valuable components of the different fractions of this plant and emphasizes its most recent food applications, demonstrating its outstanding value.

Recovery and Purification of Cutin from Tomato By-Products for Application in Hydrophobic Films.

Tomato pomace is a low-cost, renewable resource that has been studied for the extraction of the biopolyester cutin, which is mainly composed of long-chain hydroxy fatty acids. These are excellent building blocks to produce new hydrophobic biopolymers. In this work, the monomers of cutin were extracted and isolated from tomato pomace and utilized to produce cutin-based films. Several strategies for the depolymerization and isolation of monomeric cutin were explored. Strategies differed in the state of the raw material at the beginning of the extraction process, the existence of a tomato peel dewaxing step, the type of solvent used, the type of alkaline hydrolysis, and the isolation method of cutin monomers. These strategies enabled the production of extracts enriched in fatty acids (16-hydroxyhexadecanoic, hexadecanedioic, stearic, and linoleic, among others). Cutin and chitosan-based films were successfully cast from cutin extracts and commercial chitosan. Films were characterized regarding their thickness (0.103 ± 0.004 mm and 0.106 ± 0.005 mm), color, surface morphology, water contact angle (93.37 ± 0.31° and 95.15 ± 0.53°), and water vapor permeability ((3.84 ± 0.39) × 10-11 mol·m/m2·s·Pa and (4.91 ± 1.33) × 10-11 mol·m/m2·s·Pa). Cutin and chitosan-based films showed great potential to be used in food packaging and provide an application for tomato processing waste.

Protein Adsorption Performance of a Novel Functionalized Cellulose-Based Polymer.

Dicarboxymethyl cellulose (DCMC) was synthesized and tested for protein adsorption. The prepared polymer was characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and solid state nuclear magnetic resonance (ssNMR) to confirm the functionalization of cellulose. This work shows that protein adsorption onto DCMC is charge dependent. The polymer adsorbs positively charged proteins, cytochrome C and lysozyme, with adsorption capacities of 851 and 571 mg g-1, respectively. In both experiments, the adsorption process follows the Langmuir adsorption isotherm. The adsorption kinetics by DCMC is well described by the pseudo second-order model, and adsorption equilibrium was reached within 90 min. Moreover, DCMC was successfully reused for five consecutive adsorption-desorption cycles, without compromising the removal efficiency (98-99%).

Overview of Membrane Science and Technology in Portugal.

Membrane research in Portugal is aligned with global concerns and expectations for sustainable social development, thus progressively focusing on the use of natural resources and renewable energy. This review begins by addressing the pioneer work on membrane science and technology in Portugal by the research groups of Instituto Superior Técnico-Universidade de Lisboa (IST), NOVA School of Science and Technology-Universidade Nova de Lisboa (FCT NOVA) and Faculdade de Engenharia-Universidade do Porto (FEUP) aiming to provide an historical perspective on the topic. Then, an overview of the trends and challenges in membrane processes and materials, mostly in the last five years, involving Portuguese researchers, is presented as a contribution to a more sustainable water-energy-material-food nexus.

Protein Crystallization in a Microfluidic Contactor with Nafion®117 Membranes.

Protein crystallization still remains mostly an empirical science, as the production of crystals with the required quality for X-ray analysis is dependent on the intensive screening of the best protein crystallization and crystal's derivatization conditions. Herein, this demanding step was addressed by the development of a high-throughput and low-budget microfluidic platform consisting of an ion exchange membrane (117 Nafion® membrane) sandwiched between a channel layer (stripping phase compartment) and a wells layer (feed phase compartment) forming 75 independent micro-contactors. This microfluidic device allows for a simultaneous and independent screening of multiple protein crystallization and crystal derivatization conditions, using Hen Egg White Lysozyme (HEWL) as the model protein and Hg2+ as the derivatizing agent. This microdevice offers well-regulated crystallization and subsequent crystal derivatization processes based on the controlled transport of water and ions provided by the 117 Nafion® membrane. Diffusion coefficients of water and the derivatizing agent (Hg2+) were evaluated, showing the positive influence of the protein drop volume on the number of crystals and crystal size. This microfluidic system allowed for crystals with good structural stability and high X-ray diffraction quality and, thus, it is regarded as an efficient tool that may contribute to the enhancement of the proteins' crystals structural resolution.

Bio-Based Sensors for Smart Food Packaging-Current Applications and Future Trends.

Intelligent food packaging is emerging as a novel technology, capable of monitoring the quality and safety of food during its shelf-life time. This technology makes use of indicators and sensors that are applied in the packaging and that detect changes in physiological variations of the foodstuffs (due to microbial and chemical degradation). These indicators usually provide information, e.g., on the degree of freshness of the product packed, through a color change, which is easily identified, either by the food distributor and the consumer. However, most of the indicators that are currently used are non-renewable and non-biodegradable synthetic materials. Because there is an imperative need to improve food packaging sustainability, choice of sensors should also reflect this requirement. Therefore, this work aims to revise the latest information on bio-based sensors, based on compounds obtained from natural extracts, that can, in association with biopolymers, act as intelligent or smart food packaging. Its application into several perishable foods is summarized. It is clear that bioactive extracts, e.g., anthocyanins, obtained from a variety of sources, including by-products of the food industry, present a substantial potential to act as bio-sensors. Yet, there are still some limitations that need to be surpassed before this technology reaches a mature commercial stage.

Decolorization of a Corn Fiber Arabinoxylan Extract and Formulation of Biodegradable Films for Food Packaging.

Corn fiber from the corn starch industry is a by-product produced in large quantity that is mainly used in animal feed formulations, though it is still rich in valuable components, such as arabinoxylans, with proven film-forming ability. During arabinoxylans' recovery under alkaline extraction, a dark-colored biopolymer fraction is obtained. In this work, a purified arabinoxylan extract from corn fiber with an intense brownish color was decolorized using hydrogen peroxide as the decolorizing agent. Biodegradable films prepared by casting the decolorized extract exhibited a light-yellow color, considered more appealing, envisaging their application in food packaging. Films were prepared with glycerol as plasticizer and citric acid as cross-linker. Although the cross-linking reaction was not effective, films presented antioxidant activity, a water vapor permeability similar to that of non-decolorized films, and other polysaccharides' and mechanical properties that enable their application as packaging materials of low-water-content food products.

Understanding the Barrier and Mechanical Behavior of Different Nanofillers in Chitosan Films for Food Packaging.

The continuous petroleum-based plastics manufacturing generates disposal issues, spreading the problem of plastic pollution and its rise in the environment. Recently, innovative techniques and scientific research promoted biopolymers as the primary alternative for traditional plastics, raising and expanding global bioplastic production. Due to its unmatched biological and functional attributes, chitosan (Ch) has been substantially explored and employed as a biopolymeric matrix. Nevertheless, the hydrophilicity and the weak mechanical properties associated with this biopolymer represent a significant intrinsic restriction to its implementation into some commercial applications, namely, in food packaging industries. Distinct methodologies have been utilized to upgrade the mechanical and barrier properties of Ch, such as using organic or inorganic nanofillers, crosslinkers, or blends with other polymers. This review intends to analyze the most recent works that combine the action of different nanoparticle types with Ch films to reinforce their mechanical and barrier properties.

Block Copolymer-Based Magnetic Mixed Matrix Membranes-Effect of Magnetic Field on Protein Permeation and Membrane Fouling.

In this study, we report the impact of the magnetic field on protein permeability through magnetic-responsive, block copolymer, nanocomposite membranes with hydrophilic and hydrophobic characters. The hydrophilic nanocomposite membranes were composed of spherical polymeric nanoparticles (NPs) synthesized through polymerization-induced self-assembly (PISA) with iron oxide NPs coated with quaternized poly(2-dimethylamino)ethyl methacrylate. The hydrophobic nanocomposite membranes were prepared via nonsolvent-induced phase separation (NIPS) containing poly (methacrylic acid) and meso-2,3-dimercaptosuccinic acid-coated superparamagnetic nanoparticles (SPNPs). The permeation experiments were carried out using bovine serum albumin (BSA) as the model solute, in the absence of the magnetic field and under permanent and cyclic magnetic field conditions OFF/ON (strategy 1) and ON/OFF (strategy 2). It was observed that the magnetic field led to a lower reduction in the permeate fluxes of magnetic-responsive membranes during BSA permeation, regardless of the magnetic field strategy used, than that obtained in the absence of the magnetic field. Nevertheless, a comparative analysis of the effect caused by the two cyclic magnetic field strategies showed that strategy 2 allowed for a lower reduction of the original permeate fluxes during BSA permeation and higher protein sieving coefficients. Overall, these novel magneto-responsive block copolymer nanocomposite membranes proved to be competent in mitigating biofouling phenomena in bioseparation processes.

Purification of Arabinoxylans from Corn Fiber and Preparation of Bioactive Films for Food Packaging.

Corn fiber, a by-product of the starch industry, is presently incorporated in animal feed. However, it has arabinoxylans as added-value components (besides ferulic acid) that should be valorized. In this work, the raw material, a fraction enriched in arabinoxylans from corn fiber, previously produced by alkaline extraction from corn fiber and pre-concentrated by ultrafiltration, was further purified. The use of ultrafiltration operated in diafiltration mode (dia-ultrafiltration) was evaluated for the purification of the arabinoxylans fraction. The objective was to maximize the removal of the small contaminants from the fraction and to maximize the permeability and/or the permeate flux, by selecting the relevant operating conditions involved in this process. The removal of contaminants (%) was estimated when their apparent rejection stabilized. Edible films were produced, from the resultant purified arabinoxylans fraction, using glycerol as plasticizer (30% dry basis). Additionally, films with the incorporation of ferulic acid were developed, in order to obtain barriers with antioxidant activity. The films were characterized in terms of mechanical properties, antioxidant activity and permeability to water vapor. The films prepared presented a good potential to be used as packaging for food products with low water content.

Chitosan Composites in Packaging Industry-Current Trends and Future Challenges.

Chitosan-based composites play an important role in food packaging applications and can be used either as films or as edible coatings. Due to their high costs and lower performance (i.e., lower barrier against water vapor, thermal, and mechanical properties) when compared to the traditional petroleum-based plastics, the use of such biopolymers in large-scale is still limited. Several approaches of chitosan composites in the packaging industry are emerging to overcome some of the disadvantages of pristine polymers. Thus, this work intends to present the current trends and the future challenges towards production and application of chitosan composites in the food packaging industry.

A Novel Cellulose-Based Polymer for Efficient Removal of Methylene Blue.

A novel cellulose-based cross-linked polymer, dicarboxymethyl cellulose (DCMC), has been synthesized and used for methylene blue (MB) removal. Inductively coupled plasma atomic emission spectrometry (ICP-AES), Fourier-transform infrared spectroscopy (FTIR), nitrogen porosimetry, and optical microscopy were employed to characterize the structure of the cellulose-based adsorbent. The number of carboxylate groups per gram of polymer (CG) was calculated with sodium content determined by ICP-AES. Systematic equilibrium and kinetic adsorption studies were performed to assess the polymer suitability for dye removal. The effect of pH on its adsorption capacity was also studied and the equilibrium adsorption data was analyzed using Langmuir, Freundlich, and Sips isotherms. At pH = 3, the adsorption isotherms followed the Langmuir model with a maximum adsorption capacity of 887.6 mg/g. At pH = 6.4, the adsorption isotherms produced S-shape curves and were best fitted with the Sips model. The maximum MB uptake increased to 1354.6 mg/g. Pseudo first-order and second-order models were used to fit the kinetic data. A pseudo second-order kinetic model provided the best correlation for the adsorption of MB onto DCMC. Adsorption coupled with membrane filtration achieved 95% methylene blue removal and DCMC can be successfully regenerated and reused in consecutive experiments.

Electrospun asymmetric membranes for wound dressing applications.

To accomplish a rapid wound healing it is necessary to develop an asymmetric membrane with interconnected pores consisting of a top layer that prevents rapid dehydration of the wound and bacteria penetration and a sub-layer with high absorption capacity and bactericidal properties. Polycaprolactone (PCL)/polyvinyl acetate (PVAc) asymmetric membranes loaded with the bactericidal monoterpene carvacrol (CRV) were synthesized and characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Mechanical properties in dry and wet conditions and fluid handling behavior were also assessed. In addition, biological studies regarding their bactericidal effects, cytocompatibility and wound closure properties were also developed. Loading efficiencies of 40-50% were achieved in the prepared samples and 85-100% of the loaded CRV was released in simulated wound pH evolution medium. The significant inhibition of Gram negative (Escherichia coli S17) and Gram positive (Staphylococcus aureus ATCC 25923) bacteria growth clearly showed the suitability of the fabricated membranes for wound healing applications. Furthermore, cytocompatibility of the loaded membranes was demonstrated both in 2D and 3D human dermal fibroblast cultures, as well as cell migration was not impaired by released carvacrol from the membranes. These results highlight the potential of these polymeric electrospun membranes for wound healing.

Experimental Evaluation of the Thermal Polarization in Direct Contact Membrane Distillation Using Electrospun Nanofiber Membranes Doped With Molecular Probes.

Membrane distillation (MD) has recently gained considerable attention as a valid process for the production of fresh-water due to its ability to exploit low grade waste heat for operation and to ensure a nearly feed concentration-independent production of high-purity distillate. Limitations have been related to polarization phenomena negatively affecting the thermal efficiency of the process and, as a consequence, its productivity. Several theoretical models have been developed to predict the impact of the operating conditions of the process on the thermal polarization, but there is a lack of experimental validation. In this study, electrospun nanofiber membranes (ENMs) made of Poly(vinylidene fluoride) (PVDF) and doped with (1, 10-phenanthroline) ruthenium (II) Ru(phen)3 were tested at different operating conditions (i.e., temperature and velocity of the feed) in direct contact membrane distillation (DCMD). The temperature sensitive luminophore, Ru(phen)3, allowed the on-line and non-invasive mapping of the temperature at the membrane surface during the process and the experimental evaluation of the effect of the temperature and velocity of the feed on the thermal polarization.

Influence of Magnetic Nanoparticles on PISA Preparation of Poly(Methacrylic Acid)-b-Poly(Methylmethacrylate) Nano-Objects.

This article presents the synthesis of poly(methacrylic acid)-b-poly(methyl methacrylate) diblock copolymer via polymerization-induced self-assembly in the presence of iron-oxide nanoparticles. Detailed phase diagrams with and without inorganic nanoparticles were constructed. Scanning transmission electron microscopy and energy dispersive X-ray photometry studies confirme the decoration of the polymeric nanoparticles with the iron-oxide nanoparticles. These hybrid nanoparticles were used to prepare porous thin film membranes by spin coating. Finally, the magneto-responsive properties of the membranes were assessed using water filtration tests in the presence and absence of a magnetic field.

Development and characterisation of hybrid polysaccharide membranes for dehydration processes.

The purpose of this work is the development and characterisation of new hybrid polysaccharide (FucoPol) membranes. These membranes were prepared by incorporation of a SiO2 network homogeneously dispersed by using a sol-gel method with GPTMS as a crosslinker silica precursor. They were further crosslinked with CaCl2 for reinforcement of mechanical properties and improvement of their permeation performance. They were characterised in terms of their structural, mechanical and thermal properties. They presented a dense and homogeneous structure, resistant to deformation, with a Tg of 43 °C and a thermal decomposition between 240 and 251 °C. The hybrid FucoPol membranes were tested for ethanol dehydration by pervaporation and also for nitrogen dehydration. They exhibited high water selectivity values, similar to PERVAP® 4101, however they lost their stability when exposed to solutions of 10.0 wt.% water in ethanol. In contrast, these membranes were stable when applied in N2 dehydration, leading to reproducible performance and very high water selectivities.

Comparison of different coating techniques on the properties of FucoPol films.

Plasma deposition, liquid flame spray (LFS) and atomic layer deposition (ALD) were used to form inorganic coatings in new exopolysaccharide (FucoPol) biodegradable films. Coated films were characterised in terms of surface, optical and barrier properties in order to evaluate their potential use in food packaging. FucoPol films presented dense and homogeneous surface with instant water contact angle of 95̊. Plasma deposition of perfluorohexane (PFH) on FucoPol surface has not shown significant improvement in the hydrophobic behaviour over the time. The FucoPol coating of SiO2 nanoparticles deposited by LFS and plasma deposition of PFH have shown higher instant water contact angle (135°) caused by coating surface roughness, but this hydrophobic behaviour was not stable over time. FucoPol films coated only with TiO2 deposited by ALD and combination of that with plasma deposition of PFH have shown stable water contact angle during time (90̊ and 115̊, respectively), transparency in the same order of magnitude and significantly lower permeability to water vapour (3.45×10-11mol/m s Pa and 3.45×10-11mol/m s Pa when compared to uncoated films with 5.32×10-11mol/m s Pa). Moreover, films coated with TiO2-PFH have also shown a permeability to oxygen of 1.70×10-16molm/m2sPa which is 67% lower than uncoated films.

Concentration of Tea Extracts by Osmotic Evaporation: Optimisation of Process Parameters and Effect on Antioxidant Activity.

In this work, the concentration process of three different tea extracts (medicinal Rosil No. 6, Black, and Forest Fruit teas) using the osmotic evaporation (OE) process, was studied. The effect of the OE process on the content of phenolic compounds and antioxidant activity was evaluated. The concentration process was carried out in a hollow-fibre membrane contactor with an effective surface area of 0.54 m². The tea extract was circulated through the shell side of the contactor, while a concentrated osmotic solution (CaCl2 5 M) was circulated inside the fibres. The flux, the driving force, and the mass transfer coefficient were evaluated. A decrease of the water flux over time was observed and was attributed only to the decrease of the driving force, caused by the dilution of the osmotic solution. Using a surface area/feed volume ratio of 774 m²·m-3, it is possible to reach a tea concentration of 40% (w/w) in 5 h, with a constant water flux and without losing the phenolic content and antioxidant potential in most teas.