Film-forming Solutions Research Articles

Film-Forming Polymers for Inhibition of Hydroxyapatite Dissolution: A Screening Study

The aim of this study was to evaluate the effect of film-forming polymer solutions of different concentrations and pH values, either associated or not with sodium fluoride (F; 225 ppm F⁻), when applied during the initial stage of salivary pellicle formation, to prevent the dissolution of hydroxyapatite (HA), which was determined by the pH-stat method. Polyacrylic acid (PA), chitosan, sodium linear polyphosphate (LPP), polyvinyl methyl ether/maleic anhydride (PVM/MA), and propylene glycol alginate (PGA) were tested in three concentrations (lower, medium, and higher), two pH values (native or adjusted), and either associated or not with F. Distilled water, F, and stannous ion+fluoride (Sn/F; 225 ppm F⁻ and 800 ppm Sn²⁺, as SnCl₂) solutions were the controls, totalizing 63 groups. HA crystals were pretreated with human saliva for 1 min to allow pellicle formation, then immersed in the experimental solutions (1 min), and exposed to saliva for another 28 min. Subsequently, they were added to a 0.3% citric acid solution (pH = 3.8), connected to a pH-stat system that added aliquots of 28 μL 0.1 N HCl for a total reaction time of 5 min. Data were analyzed with one-way ANOVA and Tukey’s tests (α = 0.05). For PA alone, the concentrations of 0.1% (native pH), 0.06%, and 0.08% (both pH adjusted) showed significantly lower HA dissolution than the negative control. PA concentrations of 0.1% and 0.08%, of both pH values, improved the effect of F against HA dissolution to a near-identical value as Sn/F. All solutions containing chitosan and LPP significantly reduced HA dissolution in comparison with the control. For chitosan, the concentration of 0.5% (in both pH values) improved the effect of F. LPP at 0.5% (native pH) and all associations of LPP with F outperformed the effect of F. Some PVM/MA solutions significantly reduced HA dissolution but PVM/MA could not improve the protection of F. PGA was incapable of reducing HA dissolution or improving F effect. It was concluded that chitosan, LPP, and some PA and PVM/MA solutions used alone were capable of reducing HA dissolution. Only PA, chitosan, and LPP were able to enhance fluoride protection, but for PA and chitosan, this was influenced by the polymer concentration.

Development, characterization and functional properties of sodium alginate-based films incorporated with Schisandra chinensis extract-natamycin complex

Because of the impact of petroleum-based polymers on environmental deterioration and the need for safe, efficient, and functional packaging films, a sodium alginate (SA)-based film incorporating a Schisandra chinensis extract (SCE)-natamycin (NA) complex was developed for the desired physical and functional properties. The incorporation of SCE-NA into SA-based films decreased the water vapor transmission rate (WVTR), moisture content (MC), and hydrophilicity of the films and improved their opacity, elongation at break (EAB), and thermal stability. Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray Diffraction (XRD) analyses showed that SA, SCE, and NA had positive interactions and compatibility. In addition, the antimicrobial activity analysis indicated that the SA-SCE-NA film-forming solutions had satisfactory antimicrobial activity against Staphylococcus aureus, Escherichia coli, Saccharomyces cerevisiae, and Aspergillus niger. SA-based composite films have been used to coat cucumbers and blueberries to extend their shelf life. Compared to the neat SA film, the shelf life of cucumbers treated with the SA-SCE-NA film increased by 6 days compared to that in the untreated group at 28 °C, and the shelf life of blueberries increased by 5 days at 4 °C, revealing its potential utilization in food packaging.

Chitin nanowhisker-containing photo-crosslinked antimicrobial gelatin films

Nearly 57 Mt of food waste are generated annually in the EU for many reasons, for instance, because of microbial food spoilage. So, actions to reduce food loss and waste are needed and active packaging could offer a new approach towards this aim. In this study, antimicrobial gelatin films were prepared via the solution casting technique and their physicochemical, optical, mechanical, structural, barrier and antimicrobial properties were analysed. First, gelatin films were photo-crosslinked with riboflavin and the photo-curation time (0–4 h) was optimized. The optimal crosslinking time was 2 h since the solubility dropped down from 100% to 30% after 2 or 4 h of UV exposure. Then, 2 types of chitin nanowhiskers (CNWs) obtained via acid hydrolysis (AH) and TEMPO-mediated oxidation processes were added in 2 concentrations (2 and 4 wt %) into the film-forming solution (FFS) as reinforcements before film photo-crosslinking. The AH-CNW at 4 wt % was chosen as an optimal CNW type and concentration because they further decreased the solubility (∼24%) of films and improved mechanical properties up to values similar to those of commercially available synthetic packaging films. Finally, various concentrations (0, 7.5, 15 and 30 wt %) of the antimicrobial compound (Nisin A®) were added to the optimized formulation which showed good antimicrobial properties on both spoilage and pathogen strains, as well as over the native microbiota of chilled sea bream fillets, sliced cold-smoked salmon and chicken breast fillets. The developed films displayed promising properties as antimicrobial packaging for myosistem foods.

Films Based on Biopolymers Incorporated with Active Compounds Encapsulated in Emulsions: Properties and Potential Applications-A Review.

The rising consumer demand for safer, healthier, and fresher-like food has led to the emergence of new concepts in food packaging. In addition, the growing concern about environmental issues has increased the search for materials derived from non-petroleum sources and biodegradable options. Thus, active films based on biopolymers loaded with natural active compounds have great potential to be used as food packaging. However, several lipophilic active compounds are difficult to incorporate into aqueous film-forming solutions based on polysaccharides or proteins, and the hydrophilic active compounds require protection against oxidation. One way to incorporate these active compounds into film matrices is to encapsulate them in emulsions, such as microemulsions, nanoemulsions, Pickering emulsions, or double emulsions. However, emulsion characteristics can influence the properties of active films, such as mechanical, barrier, and optical properties. This review addresses the advantages of using emulsions to encapsulate active compounds before their incorporation into biopolymeric matrices, the main characteristics of these emulsions (emulsion type, droplet size, and emulsifier nature), and their influence on active film properties. Furthermore, we review the recent applications of the emulsion-charged active films in food systems.

Study and Characterization of Tribofilm based on Activated Carbon-Nanochitosan Modified with Silicone Oil for Application of Self-Healing Coatings on Metal Surfaces

A tribofilm material based on activated carbon and nanochitosan modified with silicone oil has been prepared using the sol gel method with variations in the composition of activated carbon at a mass ratio of 40% wt – 60% wt at 5% wt intervals. Sampling was carried out in two stages. The first stage of the synthesis of activated carbon from palm shells using activation of 7% H3PO4 and nanochitosan derived from shrimp shells using the ionic gelation method. The second stage was mixing the tribofilm material of activated carbon, nanochitosan and silicone oil using the sol gel method to produce a film-forming solution which was then characterized including: physical, chemical, mechanical and thermal properties. The characterization results showed that the most optimum composition was the tribofilm material of activated carbon/nanochitosan/silicone oil in S1 with a mass ratio of 40%wt activated carbon which produced a density of 0.94 x 103 kg/m3, a viscosity of 28.42 cP, and a liquid surface tension of 63.5 mN/m. While the performance characteristics of the metal surface coating produce a surface roughness of 0.162 µm for aluminum metal and 0.156 µm for copper metal, friction coefficient 0.024, wear rate 0.19 mm, thermal conductivity 0.092 W/m.K, corrosion properties 1a (slight tarnish), rate corrosion rate of 2.34 mm/yr in 3.5% NaCl medium, 4.33 mm/yr in seawater medium and 11,476 mm/yr in 3% H2SO4 medium and has good self-healing properties for 3 days on carbon steel metal surfaces with corrosion scratch treatment on 3.5% NaCl media, namely almost all the scratches/cracks covered due to frictional force from galvanic corrosion with active carboxyl, amine and hydroxyl groups with the healing agent aminopropyl siloxane (NH2-R-NH-Si-O-R) which reacts with metal ion particles (M-OH) in the formation of polymer chains for new network layers.

Eco-friendly bean flour films for sustainable food packaging

The use of natural polymers in packaging development is a promising alternative to solve the environmental problems associated with petroleum-based synthetic packaging. This study proposed the production and use of black and red bean flours as a non-conventional biopolymer matrix for the development of biodegradable films. Films with 10 and 25 g of film-forming solution of black bean and red bean flour (separately) were produced by the casting technique and characterized in terms of physical-chemical, barrier and structural properties. The film with 25 g of red bean flour film-forming solution showed a tensile strength of 9.5 MPa and a water solubility of 32.9%, higher values than the other films produced. Regarding the water vapor permeability, the formulation with 10 g of film-forming solution of red bean showed the lowest value (1.3 g.mm/h.m2.kPa) when compared to the value of 2.3 g.mm/h.m2.kPa for the formulation with 25 g of film-forming solution of red bean. The films presented similar relative crystallinity and a predominantly homogeneous surface. All films presented total biodegradability in 14 days in soil, and 20 days in sea water. The red bean flour films presented better mechanical and barrier properties, and also were able to be sealed and printed. It is believed that this packaging could be used to package products such as olive oil, because in addition to containing the product, its low transparency could prevent oxidative processes caused by the light incidence.

Mild temperature-assisted antimicrobial film with self-activating biocatalytic activity for efficient preservation of perishable products

To mitigate the decay of fruits and vegetables caused by food-borne microorganisms, this contribution proposed for the first time a novel mild temperature-assisted nanozyme-based antibacterial packaging system with self-activating behavior (MnHC-CS films) through a demand-oriented tailoring process that involved the construction of hollow carbon-supported Mn3O4 fillers (MnHC) and its incorporation in chitosan (CS) matrix. In this system, the weak acidity of CS film triggers the self-activation of MnHC nanozyme. Leveraging the synergistic effects of the excellent oxidase-like activity and photothermal properties of MnHC, in conjunction with the inherent bacteria trapping and killing capabilities of CS, the MnHC0.20-CS film (The 0.20 represents the amount of MnHC in the film-forming solution) demonstrates remarkable antibacterial and antifungal performances, with high bactericidal rate, short action time, and mild heating temperature. Therefore, the MnHC0.20-CS film showcases excellent preservation capabilities, significantly extending the shelf life of kumquats by approximately 2.3 times. Additionally, this film also boasts enhanced mechanical strength, improved barrier properties, and sufficient safety, paving the way for its practical application. These exceptional features underscore the good potential of MnHC0.20-CS film in effectively safeguarding perishable products.

Bacterial cellulose nanofibers used as nanofillers improved the fresh-keeping performance of gelatin-based edible coating for fresh-cut apples.

In this study, bacterial cellulose nanofibers (BCNs) (0%, 1%, 2%, and 3%) were used as nanofillers to prepare gelatin-based edible films, and their physical properties and fresh-keeping performance were investigated. The microstructure observation showed that the BCNs were well dispersed in the gelatin-based edible films and the surface roughness of the films increased with the increase of BCNs content. X-ray diffraction and thermogravimetric analysis showed that the crystallinity and thermal stability of the film were significantly increased with the increase of BCNs. Fourier-transform infrared spectroscopy analysis suggested that hydrogen bond interactions occurred between BCNs and gelatin polymers, leading to improved mechanical properties with the increase of BCNs content. Furthermore, the barrier performance was also improved with the increase of BCNs content, where gelatin-based edible films with 2% BCNs showed the best mechanical property. Meanwhile, the gelatin-based film-forming solutions (FFSs) containing different BCNs were coated on the fresh-cut apples and the corresponding fresh-keeping performance was investigated. The results showed that the fresh-keeping parameters of fresh-cut apples coated with FFSs containing BCNs were better as compared with those of pure gelatin FFSs. Moreover, the fresh-keeping parameters were improved with the increase of BCNs, especially the FFSs containing 2% BCNs that showed the best fresh-keeping parameters. Therefore, BCNs, used as nanofillers, are an excellent enhancer to improve the fresh-keeping performance of the gelatin-based edible coating, showing a promising potential application in the food preservation field.

An intelligent chitosan/gelatin film via improving the anthocyanin-induced color recognition accuracy for beef sub-freshness differentiation monitoring

A novel volatile amine-responsive food freshness smart film, CG-BAE, has been developed utilizing chitosan (CS) and gelatin (GL) as film substrates and butterfly pea flower anthocyanin extract (BAE) as the indicator. The pH value of the film-forming solution was found to significantly impact the physical properties, biogenic amine response sensitivity, and initial color of the film. The hydrogen bonding interaction between anthocyanins and the film matrix was identified as the main binding force, as confirmed by FT-IR spectroscopy and molecular docking simulation analysis. Notably, CG-BAE-2.0 films have demonstrated excellent color stability, antioxidant activity, and color responsiveness. The performance of the film in monitoring beef freshness was evaluated and proved clear differentiation between four stages: freshness, sub-freshness, onset of spoilage, and complete spoilage. The color change of the film was assessed using RGB values obtained from a smartphone App, reducing the difference in color recognition by individual naked eyes. Therefore, this work addresses the limitation that BAE-based intelligent films cannot be distinguished at the starting point of meat spoilage, and presents a promising approach to sub-freshness indication, opening new possibilities for food freshness differentiation monitoring.

Effect of waste Dunaliella tertiolecta biomass ethanolic extract and turmeric essential oil on properties of guar gum-based active films

The presented work focuses on the development of guar gum-based active films infused with two bio-fillers such as crude algae ethanolic extract (CAEE) and turmeric essential oil (TEO). Besides, the waste biomass of Dunaliella tertiolecta (after oil extraction) was utilized in this study to obtain CAEE. The CAEE was extracted using ultrasound-assisted technology. The influence of varying concentrations of TEO (0.5%, 1%, and 2%) at fixed CAEE concentration on the film properties including mechanical, morphological, optical, thermal, water vapor barrier, antioxidant, and antimicrobial activity was investigated. The rheological properties of the film-forming solution were also analyzed. The incorporation of CAEE and TEO improved elongation at the break value of films by ∼18% and reduced the water vapor transmission rate by ∼35%. The results of thermal stability indicated that the active films were stable at the temperature range of 25–80 °C. The increasing surface roughness, hydrophobicity, and reduction in transparency (∼32%) with UV-light blocking properties were exhibited by the developed films with increasing TEO concentration. The non-Newtonian pseudoplastic behavior was found in film-forming solutions. Furthermore, the developed active films demonstrated superior (p < 0.05) antioxidant properties and antimicrobial behavior against two known food pathogens namely, Escherichia coli and Staphylococcus aureus. Therefore, the findings of the study stipulated the synergistic effect of CAEE and TEO incorporated guar gum-based films as excellent active films. Moreover, this study could contribute to the utilization of biowaste and the development of sustainable active packaging materials that would enhance food quality and safety.

Production of PVA-chitosan films using green synthesized ZnO NPs enriched with dragon fruit extract envisaging food packaging applications

In this work, the PVA-chitosan composite packaging films doped with biomass-fabricated zinc oxide nanoparticles (ZnO NPs) and dragon fruit waste extract (DFE) were developed for potential use in food packaging applications. ZnO NPs were synthesized using a sustainable method employing C. sinensis waste extract as a reducing agent. Chitosan and PVA were blended in a specific ratio (1: 1 w/w) to obtain a film-forming solution, into which the ZnO NPs and dragon fruit waste extract were incorporated. The resulting solution was cast into films, which were characterized using various analytical techniques. Mechanical properties, water solubility, and thermal stability of the films were also evaluated. The results demonstrated that the incorporation of green ZnO NPs and dragon fruit waste extract enhanced the mechanical strength and thermal stability of the films while reducing water vapor permeability. Moreover, the films exhibited biocidal and excellent 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging properties, indicating their use in the food packaging sector. The production of these films offers a practical approach to produce bioactive food packaging materials. The use of plant extract and waste material as reducing agents can reduce the overall cost of production while providing added benefits, such as antioxidant and antibacterial properties.

Extraction of Fish Protein Concentrates from Discards and Combined Application with Gelatin for the Development of Biodegradable Food Packaging

Fish waste accounts for almost one-third of the total fish production annually. The main objective of this study was to upcycle fish by-products to produce biodegradable packaging materials. Fish protein concentrate (FPC) was extracted from gilthead seabream by-catch (flesh and skin). FPC (3%) and gelatin (3%) were used to produce film-forming solutions. The films were produced according to the solvent casting method. The produced films were tested as packaging materials via the determination of different film properties. The wettability of the packaging materials was characterized based on the determination of the contact angle. Water vapor permeability was evaluated using the ASTM E96/E96M standardized method. The evaluation of mechanical properties was based on the Young’s modulus, tensile strength, and elongation at break. Color was measured using a CIELab system. The incorporation of FPC into the produced membranes resulted in a reduced contact angle from 108.5° to 90.6°; however, both films were characterized as hydrophobic materials. Films supplemented with FPC had lower tensile strength values compared to pure gelatin films, but higher elongation values without statistically significant differences. The color parameters (L,a,b) indicated that gelatin films and FPC–gelatin films were colorless and transparent (L &gt; 90), an important parameter for food packaging materials. The production of biodegradable packaging materials from FPC and gelatin may effectively reduce petroleum-based plastics under the circular economy model.

Impact of edible coatings reinforced with mesoporous silica nanoparticles added with cinnamon and lemongrass essential oils applied on sourdough bread

Active edible coatings may be used to increase the shelf life of food products, free of chemical additives. An edible coating comprising chitosan (CH) and quinoa protein (QP), incorporated with lemongrass and cinnamon essential oils (LEO and CEO, respectively) encapsulated in mesoporous silica nanoparticles (MSN) (6% w/v) was developed, and further applied on sourdough bread to evaluate its shelf life. Films were prepared at two QP:CH ratios, 4:1 and 9:1 (w/w), containing the essential oils (EO) encapsulated in MSN (individually or in 1:1 or 2:1 LEO:CEO ratios, v/v mixture). EO were extracted by steam distillation, and the antifungal effect of both oils alone and in mixture was preserved after encapsulation in MSN. The films were tested for mechanical, antifungal, and barrier properties. Films at 4:1 QP:CH ratio (w/w), added with EO (2:1 LEO:CEO ratio) encapsulated in MSN showed the best mechanical (tensile strength of 28 MPa) and barrier [5.11 × 10−5±6.4 × 10−7 g/(day*m*Pa)] properties, an antifungal index of 95%. The film-forming solution was used to coat sourdough bread, to evaluate its impact on shelf life and sensory properties. The coated bread showed low hardness (49 N) up to 10.5 d of accelerated storage conditions, indicating delayed bread staling, while at the same time preventing color loss and microbial spoilage. Coated breads were found sensory acceptable by 60 untrained panelists.

Structural, thermal, optical, and mechanical properties of composite films developed from the button mushroom (Agaricus bisporus)-sourced high molecular weight chitosan and potato starch

Films were fabricated using the button mushroom (Agaricus bisporus) sourced high molecular weight chitosan with or without potato starch using the casting method. Glycerol was used as the plasticizer. Chitosan content in the film-forming solution (FFS) was varied (0.5, 0.75 and 1.0% w/v of FFS) while potato starch (1.0% of FFS) and glycerol (25% of the total solid content in the solution) contents were not varied. The control sample contained only chitosan (1.0% of the FFS) and glycerol. The effect of increasing the content of chitosan on the rheological properties of FFS and the properties of the films were investigated. The FFS's shear viscosity and shear modulus (elastic and viscous components) increased with increasing chitosan content. Morphological examination revealed that the films exhibited a compact structure devoid of large pores and cracks. Surface roughness captured with an atomic force microscope was reduced (19-6 nm) with increasing content of chitosan in the film. The films exhibited two hydrated crystalline phases at 9 and 20o. Light transmittance and glossiness of the films were enhanced with increasing chitosan content. FTIR analysis indicated the increasing availability of reactive sites with the increasing content of chitosan leading to an enhanced hydrogen bonds network and increased cohesion of the film structure. This may be the reason for improved mechanical properties and reduced water vapour permeability of the films with increasing chitosan content.

Developing a pachyman/polyvinyl alcohol-polylactic acid bilayer film as multifunctional packaging and its application in cherry tomato preservation

Polyvinyl alcohol (PVA) is a widely used biodegradable material, but its high solubility and water vapor permeability limit its applications in food packaging. To address this issue, bilayer films were developed based on the combination of blending and coating techniques in the study, which consisted of an inner pachyman (PM)/PVA blend layer and an outer polylactic acid (PLA) layer. Blending PVA with PM reduced the solubility and oxygen permeability of the film, and the blend matrix showed rapid self-healing capabilities. Loading of a thin PLA shell onto the PM/PVA layer improved the water resistance, tensile strength, stiffness and water vapor barrier of the developed bilayer films. The best overall performance of the bilayer film was achieved using 40 g/L PLA as the film-forming solution. Infrared spectroscopic and microscopic structure analysis revealed weak interfacial interaction of the bilayer film. Furthermore, this bilayer film showed a better preservation effect on cherry tomatoes compared with PVA, polyethylene, and PM/PVA films. The physicochemical quality of fruits could be effectively preserved for at least 10 days under ambient environment. It is anticipated that the bilayer film developed here serves as a promising candidate for food packaging materials to extend the shelf life.

Development of edible films by incorporating nanocrystalline cellulose and anthocyanins into modified myofibrillar proteins.

In this study, a myofibrillar protein (MP) system was used to investigate the film properties changes by adjusting the intensity of the interaction of proteins with other food components. The structure and rheological properties of several film-forming solutions were then determined. Furthermore, the structure of these composite films was examined using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The smooth and uniform surface acquired by scanning electron microscopy (SEM) substantiated the increased compatibility and continuity observed for films with greater food component interaction. In addition, the MP-based edible films with stronger food component interactions (the MP-Myr/ANT/NCC group) displayed superior mechanical (tensile strength: 6.68MPa, elongation at break: 94.43%), water vapor barrier (10.01×10-9gm-1s-1Pa-1), and ammonia sensitivity (total color difference: 17.00) capabilities compared to those of the other groups (the MP/ANT/NCC, MP-Lut/ANT/NCC, and MP-Que/ANT/NCC groups).

Sustainable starch-based edible films with agrifood residues as potential carriers for the probiotic Lactobacillus rhamnosus

Edible films are promising carriers for probiotics and can be composed by agrifood residues, which are usually rich in polymers and bioactive compounds. In this work, starch-based films were enriched with three types of agrifood residues (quince, potato and orange peels) and the incorporation of the probiotic Lactobacillus rhamnosus was studied, as well as the addition of inulin as a protective prebiotic. The resulting films were characterized in terms of mechanical properties, physicochemical properties, lactobacilli viability and microbiological properties. The mechanical properties of the films generally decreased with the introduction of L. rhamnosus, although this was highly dependent on the film composition. All films exhibited water vapor permeabilities in the typical range of starch-based films and were not greatly affected by the inclusion of probiotics. The loss of probiotic viability during films production was strongly related to the pH of the film-forming solutions. Films with agrifood residues had a slower loss of probiotic viability during storage, when compared to plain starch films, which may be explained by the presence of antioxidant compounds. Inulin was expected to improve viability, but this was not observed. Microbiological analysis showed that agrifood residues powders contained natural contaminant bacteria that were partially eliminated during film formation. Moreover, none of the target foodborne pathogens were detected in the analyzed samples. Overall, the results suggest that edible films containing agrifood residues can be a promising material for the delivery of probiotics and/or as primary packaging for some food products.

Intelligent biogenic pH-sensitive and amine-responsive color-changing label for real-time monitoring of shrimp freshness.

This study developed an intelligent, pH-sensitive and amine-responsive colorimetric label based on chitosan, whey protein and thymol blue by controlling the pH value of the film-forming solution. The obtained label was used to monitor shrimp freshness in real time. The results of this study offer a new approach for developing highly intelligent biogenic labels for freshness monitoring during seafood preservation and processing. The pH 2.0 chitosan-whey protein-thymol blue (CWT-pH 2.0) label exhibited remarkable properties, including the highest tensile strength (5.90 MPa), excellent thermal stability, low water solubility (27.80%) and highly sensitive color responsiveness. The characterization techniques of scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed the effective immobilization of thymol blue within the film-forming matrix through hydrogen bonding. Furthermore, the CWT-pH 2.0 label demonstrated visible color changes in the presence of volatile ammonia concentrations ranging from 25 to 25 000 ppm. Consequently, the label successfully facilitated real-time monitoring of shrimp freshness during storage at 4 °C. Importantly, the release rate of thymol blue from the label in food simulants was minimal, measuring only 2.53%. The CWT-pH 2.0 label exhibits significant potential as a highly intelligent biogenic label for freshness monitoring in seafood preservation and processing. © 2023 Society of Chemical Industry.

Combined Effect of Citric Acid and Polyphenol-Rich Grape Seed Extract towards Bioactive Smart Food Packaging Systems.

Alginate films (2% w·v-1) were prepared with varying concentrations (5-20% w/w) of citric acid and aqueous grape seed extract (GSE) filtrate (11.66 ± 1.32 g GAE/L) using the solvent-evaporation method. Crosslinking alginate via ester bonds (FTIR analysis) with citric acid up to 10% (w/w) led to a 33% increase in tensile strength, a 34% reduction in water vapor transmission rate (WVTR), and had no impact on elongation at break. Crosslinking alginate with citric acid in the presence of GSE increased the tensile strength by 17%, decreased WVTR by 21%, and significantly improved DPPH scavenging activity. Moreover, after incubation for 24 h at 37 °C, the film-forming solutions exhibited increased antimicrobial activity, resulting in 0.5- and 2.5-log reductions for Escherichia coli and Staphylococcus aureus, respectively, compared to the values obtained without the addition of GSE. The stronger inhibitory effect observed against Gram-positive bacteria can be attributed to the unique composition and structure of their cell walls, which creates a barrier that restricts the penetration of polyphenols into the cells. The pH adjustment of the GSE film-forming solution from 2.0 to 10.0 shifted the UV/VIS absorption spectra, resulting in a colour change from yellow to red. The findings of this study have showcased the potential of combining GSE and citric acid to enhance the functionality and bioactivity of alginate films for applications in smart food packaging.

Self-assembly of zein in aqueous acetic acid and ethanol solvents: Effect on mechanical properties of the zein film

The solubility of zein varies with solvent types, therefore, affecting the physicochemical properties of film-forming solutions (FFS) and the fabricated zein films. The transformation of α-helix to β-sheet in zein molecules varied with solvent polarity, which influenced the self-assembly of zein. In this research, zein film was fabricated using various concentrations of aqueous acetic acid solvent (AAS) and aqueous ethanol solvent (AES). Zein was soluble over 96 % in 40–80 %(v/v) AAS and 60–80 % in 75–95 %(v/v) AES, respectively. SDS-PAGE reveals that the insolubility of the β-zein and dimers of α-zein was responsible for the solubility difference. The formation of the zein network affects the mechanical and physical properties of the film. The tensile strength of the film was over 25 MPa when the β-zein was soluble, and the zeta potential of FFS was over + 25 mV. Films fabricated with AAS had at least five times higher Young’s modulus than AES films. The transformation ratio of α-helix to β-sheet and reassembling of β-sheet into strips during self-assembly depended on the water percentage in the FFS. The free water stuck in the film network contributed to the moisture content of 8–10 % in AAS films and 11–16 % in AES films in films was observed by LF NMR. This study suggested that a stable FFS (zeta potential > +40 mV) and organized network in the film could be obtained by dissolving zein in AAS (≤ 70 %, v/v) than in AES.