Excellent UV Barrier Research Articles

Multifunctional fish gelatin film incorporated with chitosan carbon dots and butterfly pea flower anthocyanins for active/smart packaging of Pacific white shrimp

A pH-responsive and active film formulated using fish gelatin incorporated with chitosan carbon dots (CDs) and butterfly pea flower (Clitoria ternatea) anthocyanins (BA) was developed and used for the packaging of Pacific white shrimp (Litopenaeus vannamei). CDs showed more effective inhibition zones against Listeria monocytogenes and Staphylococcus aureus compared to Salmonella enterica and Escherichia coli. The addition of CDs (1, 3, and 5 wt%) significantly increased (p < 0.05) the mechanical properties of gelatin film. The film containing BA and 5% CDs showed excellent UV-barrier, antioxidant, and antimicrobial properties. The functional films with 5% CD effectively inhibited the growth of L. monocytogenes within 6 h and E. coli within 9 h of incubation, respectively. The gelatin-based films combined with BA and CD showed distinct color changes with different pHs (from 2 to 12), confirming their potential for intelligent packaging purposes. Films containing BA and CD preserved shrimp quality, delayed bacterial growth, and maintained shrimp color more effectively during packaging and storage of Pacific white shrimp at 4 °C for 12 days. On the final day of storage, shrimp kept in the pouches made with 5% CD film showed the lowest total viable count and psychrophilic bacteria count (4.9 and 4.4 log CFU/mL, respectively). Therefore, gelatin-based films containing CD and BA are promising materials for antibacterial packaging films and can detect real-time quality changes in seafood.

Dual effect of pH and X-ray irradiation on properties of gelatin/trans-cinnamaldehyde-based composite films for sustainable packaging

Gelatin (Gel) based water-insoluble films with antimicrobial properties were developed by the green method using trans-cinnamaldehyde (TCA) and low-energy X-ray irradiation as dual crosslinkers. The Gel/TCA composite films (GTCF) were prepared at different pH (4, 6, 8, and 10) and crosslinked by incorporating 5 % (w/w, based on Gel) TCA and X-ray irradiation (350 kV and 11.4 mA) with doses of 0, 5, 10 and 15 kGy. The presence of TCA in GTCF forms dense, flexible, and strong films when exposed to X-ray irradiation. The GTCF at pH 6, incorporated with 5 wt% TCA and irradiated with 10 kGy X-ray, displayed the highest degree of crosslinking (DOC) (93.4 ± 3.4 %), tensile strength, excellent UV-barrier (> 99.9 %), antimicrobial (inhibitory capacity of >50 %), and water vapor permeability (4.1 ± 0.6 g.mm/m2.day. kPa), and low solubility in water (0.5 ± 0.3 %), and oxygen permeability. The GTCF, crosslinked with X-ray irradiation, has multifunctional properties and strong potential in the sustainable packaging industry to augment the shelf life of food and reduce food waste. To the best of our information, this is the first and novel report investigating the effects of pH on the properties of GTCF crosslinked with X-ray.

Fabrication of a versatile and efficient ultraviolet blocking biodegradable composite film consisting of Tara gum/PVA/Riceberry phenolics reinforced with biogenic riceberry phenolic-rich extract-nano‑silver

The demand for UV-protective and biodegradable packaging materials has been increasing with greater awareness about environmental sustainability and human safety. In this work, the effect of incorporating riceberry phenolic extract (RPE) as well as combined RPE and green synthesized biogenic nano‑silver (RPE-NS, into Tara gum/PVA (TP)-based matrix was evaluated on the physical, mechanical, functional, biocompatible and biodegradable attributes of the resultant composite films. Integration of RPE (2 wt%) and RPE-NS (0.8 wt%) resulted in nanocomposite (TP/RPE-NS) film with improved physical properties relative to the plain TP and TP/RPE films. The TP/RPE-NS film displayed a compact structure and homogenous distribution of the nano‑silver. Increased molecular interactions, crystallinity and thickness was also observed for the nanocomposite film. Compared to plain TP film, TP/RPE-NS film exhibited improved water vapor barrier properties and surface hydrophobicity due to the extract and nanoparticles. The tensile strength and elongation-at-break of TP/RPE-NS were markedly higher (41.76 MPa and 37.40 %) compared to that of plain TP film (36.07 MPa and 20.80 %). Whereas TP/RPE film provided good UV protection (UPF value of 31.85) compared to the minimal protection by TP film (UPF value of 2.72), combination of RPE/RPE-NS ensured that TP/RPE-NS availed an excellent UV-barrier performance (UPF value of 61.09). Furthermore, TP/RPE-NS film exhibited significant antioxidant activity relative to TP film. Besides, all TP-based films were found to be compatible with rat erythrocytes and biodegradable. Taken together, these findings indicate that TP/RPE-NS holds good potential for the development of UV-protective and biodegradable packaging material.

Epoxidized Soybean Oil Toughened Poly(lactic acid)/Lignin-g-Poly(lauryl methacrylate) Bio-Composite Films with Potential Food Packaging Application.

The application of lignin as a filler for poly (lactic acid) (PLA) is limited by their poor interfacial adhesion. To address this challenge, lignin-graft-poly(lauryl methacrylate) (LG-g-PLMA) was first blended with poly (lactic acid), and then epoxidized soybean oil (ESO) was also added to prepare PLA/LG-g-PLMA/ESO composite, which was subsequently hot pressed to prepare the composite films. The effect of ESO as a plasticizer on the thermal, mechanical, and rheological properties, as well as the fracture surface morphology of the PLA/LG-g-PLMA composite films, were investigated. It was found that the compatibility and toughness of the composites were improved by the addition of ESO. The elongation at break of the composites with an ESO content of 5 phr was increased from 5.6% to 104.6%, and the tensile toughness was increased from 4.1 MJ/m3 to 44.7 MJ/m3, as compared with the PLA/LG-g-PLMA composite without ESO addition. The toughening effect of ESO on composites is generally attributed to the plasticization effect of ESO, and the interaction between the epoxy groups of ESO and the terminal carboxyl groups of PLA. Furthermore, PLA/LG-g-PLMA/ESO composite films exhibited excellent UV barrier properties and an overall migration value below the permitted limit (10 mg/dm2), indicating that the thus-prepared biocomposite films might potentially be applied to environmentally friendly food packaging.

Enhanced antibacterial and antioxidant activities of chlorogenic acid loaded sweet whey/starch active films for edible food packaging

Starch and whey protein are potential biomaterials for the development of biodegradable and edible food packaging. In this study, chlorogenic acid (CGA), an eco-friendly natural extract, was firstly added to sweet whey/starch matrix as a bioactive compound to develop biodegradable active packaging materials. The results showed that when the ratio between starch and sweet whey was 10:1, water resistance and toughness of sweet whey/starch blend films were improved significantly. After the addition of CGA, the active films showed excellent UV barrier, antibacterial and antioxidant properties. When the addition of CGA reached 3%, UV barrier (at 315 nm), antibacterial (against Escherichia coli) and antioxidant (ABTS method) properties of the active films were increased by 54.6%, 47.5% and 74.5% compared with sweet whey/starch matrix. The presence of CGA could form new hydrogen bonds in the matrix and affect the interactions between sweet whey and starch, which increased swelling rate and toughness of the active films. Preservation experiments of fresh bananas could indicate that the presence of CGA can effectively exert antioxidant effects and inhibit the browning of bananas. As an edible inner coating or film, CGA loaded sweet whey/starch active material has good application potential in the field of food packaging.

Development of Sustainable and Active Food Packaging Materials Composed by Chitosan, Polyvinyl Alcohol and Quercetin Functionalized Layered Clay.

In order to solve the problems of insufficient active functions (antibacterial and antioxidant activities) and the poor degradability of traditional plastic packaging materials, biodegradable chitosan (CS)/polyvinyl alcohol (PVA) nanocomposite active films reinforced with natural plant polyphenol-quercetin functionalized layered clay nanosheets (QUE-LDHs) were prepared by a solution casting method. In this study, QUE-LDHs realizes a combination of the active functions of QUE and the enhancement effect of LDHs nanosheets through the deposition and complexation of QUE and copper ions on the LDHs. Infrared and thermal analysis results revealed that there was a strong interface interaction between QUE-LDHs and CS/PVA matrix, resulting in the limited movement of PVA molecules and the increase in glass transition temperature and melting temperature. With the addition of QUE-LDHs, the active films showed excellent UV barrier, antibacterial, antioxidant properties and tensile strength, and still had certain transparency in the range of visible light. As QUE-LDHs content was 3 wt%, the active films exhibited a maximum tensile strength of 58.9 MPa, representing a significant increase of 40.9% compared with CS/PVA matrix. Notably, the UV barrier (280 nm), antibacterial (E. coli) and antioxidant activities (DPPH method) of the active films achieved 100.0%, 95.5% and 58.9%, respectively. Therefore, CS/PVA matrix reinforced with QUE-LDHs has good potential to act as an environmentally and friendly active packaging film or coating.

Smart and UV-Resistant Edible Coating and Films Based on Alginate, Whey Protein, and Curcumin.

In this work, smart edible coating and films with excellent UV barrier properties were prepared from alginate, whey protein isolate, and curcumin. The primary focus of this investigation centered on assessing the impact of whey protein and curcumin on the physical and functional properties of the alginate films. Whey protein reduced the film transparency while simultaneously enhancing the hydrophobicity and antioxidant properties of the alginate film. Curcumin imparted a yellow hue to the film, consequently decreasing the transparency of the film. It also substantially improved hydrophobicity, antioxidant activity, and UV-blocking efficiency within the films. Remarkably, curcumin demonstrated a significant reduction in the water vapor transmission rate of the film. For the preservation of apples, a higher concentration of curcumin was required, which effectively suppressed the respiration rate and moisture loss post-harvest, resulting in an extended shelf-life for the apples. As a result, the coated apples exhibited significantly reduced enzymatic browning and weight loss in comparison to their uncoated counterparts. Furthermore, these curcumin-containing films underwent a reversible color change from orange to red when exposed to ammonia vapor. This attribute highlights the potential of the developed coating and film as a smart, active food packaging solution, particularly for light-sensitive food products.

Ductile, High-Lignin-Content Thermoset Films and Coatings.

In the context of transitioning toward a more sustainable use of natural resources, the application of lignin to substitute commonly utilized petroleum-based plastics can play a key role. Although lignin is highly available at low cost and presents interesting properties, such as antioxidant and UV barrier activities, its application is limited by its low reactivity, which is a consequence of harsh conditions normally used to extract lignin from biomass. In this work, the use of glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups and hence highly reactive toward epoxy cross-linkers, is presented. GA lignin, which is directly extracted from biomass via a one-step aldehyde-assisted fractionation process, allowed the preparation of thermoset films and coatings via a simple reaction with sustainable poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether cross-linkers. This allows one to prepare freestanding films containing up to 70 wt % lignin with tunable mechanical properties and covalently surface-attached coatings containing up to 90 wt % lignin with high solvent resistance. Both films and coatings display antioxidant properties and combine excellent UV barrier activity with high visible transparency, which is attractive for applications in sustainable food packaging.

Enhanced mechanical and functional properties of chitosan/polyvinyl alcohol/hydroxypropyl methylcellulose/alizarin composite film by incorporating cinnamon essential oil and tea polyphenols

In this study, cinnamon essential oil and tea polyphenols were added to chitosan/ polyvinyl alcohol/ hydroxypropyl methylcellulose/ alizarin composite films to enhance their mechanical and functional properties. Their addition to the composite films enhanced their antibacterial and antioxidant properties and significantly improved its elongation at break (p < 0.05). Cinnamon essential oil reduced the water vapor permeability, water content, and water solubility of composite films and improved their transparency. The composite films with additive exhibited excellent UV-barrier ability and pH responsivity. Fourier Transform infrared spectroscopy and X-Ray Diffraction analyses confirmed hydrogen bond formation between the polymer molecules and additives. The results of Scanning Electron Microscope-Focused Ion Beam revealed improved surface and cross-section morphology of the films, leading to the generation of a cross-linked structure. Thermogravimetric and differential scanning calorimetry analysis indicated enhanced thermal stability of the composite films upon cinnamon essential oil addition. Analysis of storage quality indicators (TBARS value, TVC, and TVB-N) revealed that the composite films could prolong the freshness of surimi. The incorporation of cinnamon essential oil and tea polyphenols into the composite films has demonstrated significant potential as an effective and natural alternative for active food packaging.

Ultraviolet blocking ability, antioxidant and antibacterial properties of newly prepared polyvinyl alcohol-nanocellulose‑silver nanoparticles-ChunJian peel extract composite film

In this work, nanocellulose (CNC) from waste water chestnut (WCT) shell was firstly used for preparing nanocomposite films, by using ChunJian peel extract (CJPE) as a green reducing agent to synthesize silver nanoparticles (AgNPs), and then loading them into polyvinyl alcohol-nanocellulose (PVA-CNC) matrix, a multifunctional nanocomposite material that could be used in food packaging was developed. The prepared films were tested for mechanical strength, barrier properties, thermal properties, antibacterial, antioxidant and biocompatibility through various characterizations. The PVA-CNC-AgNPs-CJPE film had good thermostability, mechanical strength, barrier properties, and biocompatibility. Compared with pure PVA film and PVA-CNC film, PVA-CNC-AgNPs-CJPE could shield over 95 % of the UVB (320–275 nm) spectrum and UVC (275–200 nm) spectrum and most of the UVA (400–320 nm). By disk diffusion analysis, the inhibition zones of PVA-CNC-AgNPs-CJPE film against E. coli, P. aeruginosa, S. aureus and E. faecalis were 22.3 mm, 25.0 mm, 22.0 mm and 19.3 mm, respectively. The milk antibacterial simulation test confirmed that PVA-CNC-AgNPs-CJPE film could effectively limit bacterial reproduction and prolong the shelf life of milk. PVA-CNC-AgNPs-CJPE film had excellent UV barrier properties, good antioxidant properties and high-efficiency antibacterial activity, which is expected to be widely used in sustainable nanocomposite food packaging.

Gelatin/carrageenan-based smart packaging film integrated with Cu-metal organic framework for freshness monitoring and shelf-life extension of shrimp

A gelatin/carrageenan (Gel/Car) based antibacterial and pH-responsive intelligent film was developed by incorporating a Cu-metal organic framework (Cu-MOF) and anthocyanins from red cabbage (Brassica oleracea). Cu-MOF and anthocyanin were mixed compatibly with the polymer matrix to form a dense, flexible, and strong film. The film incorporated with 3 wt% Cu-MOF displayed excellent UV-barrier ability (98.5% in the UV-A and 99.9% in the UV-B), strong antioxidant efficacy against ABTS (100%), and DPPH (100%) and exhibited strong antibacterial activity to completely stop the growth of Gram-positive and Gram-negative bacteria after 3 h of incubation. In addition, the film exhibited pH-dependent color change under various pH conditions (pH 2 to 12), and freshness monitoring tests of shrimp demonstrated a qualitative and quantitative color change of the film (decreasing the redness, a-value, from 24.5 to 3.7). In packaging experiments using shrimp, this packaging film delayed the quality change rate of foods during storage and extended the shelf life of these foods. The gelatin/carrageenan-based multifunctional film combined with a Cu-metal organic framework is expected to help visualize food changes before consumption, extend processed foods' shelf life, and significantly reduce food waste problems.

Grafting Polymerization of Long-Chain Hydrophobic Acrylic Monomer onto Lignin and Its Application in Poly(Lactic Acid)-Based Wholly Green UV Barrier Composite Films.

The development of low-cost and high-performance bio-based composites derived from forestry waste lignin and polylactic acid has emerged as a topic of central attention. However, the weak compatibility between lignin and polylactic acid often resulted in high brittleness of the composites. Graft copolymerization is not only the most effective way to modify lignin but also can significantly improve the compatibility of lignin and polylactic acid. In this study, bio-based monomer lauryl methacrylate was grafted onto lignin by feasible radical polymerization to prepare lignin graft copolymers with excellent thermal stability and hydrophobicity, which are expected to improve the compatibility with polylactic acid. Wholly bio-based composites were prepared by compounding this graft copolymer with polylactic acid. The results showed that the crystallization ability of the composite was improved, and the highest crystallinity was increased from 6.42% to 17.46%. With addition of LG-g-PLMA lower than 9%, the thermal stability of the composites was slightly improved. At 5% copolymer addition, the elongation at break and tensile toughness of the composites increased by 42% and 36%, respectively. Observation of the frozen fracture surface of the composite by SEM found that wire drawing and ductile deformation appeared when a small amount of LG-g-PLMA was added. The thus prepared composites also showed excellent UV barrier properties. This approach provides a new idea for the high-value application of lignin.

Preparation of alkali-soluble polysaccharide from Clausena lansium (Lour.) Skeels and its effects on properties of chitosan-based edible film

In this study, alkali-soluble polysaccharide from wampee (ASP-W) was prepared and its effect on chitosan-based composite film was investigated. Preliminary characterization of ASP-W showed it was a kind of typical homogeneous polysaccharide, with a molecular weight of 1.5 × 103 KDa. Infrared spectroscopy proved the successful combination of ASP-W with chitosan. Meanwhile, composite film exhibited increased thickness, water solubility percentage, and swelling ratio and decreased moisture content. In terms of optical transmittance, composite films showed excellent UV barrier capability below 400 nm. Mechanical tests demonstrated tensile strength up to 24.84 MPa at ASP-W 1.5% and elongation at break up to 27.93% at ASP-W 4.5%. Composite films also possessed better barrier properties. Differential scanning calorimeter (DSC) results also indicated better thermostability of composite films. DPPH radical scavenging reached 46.84% at ASP-W 1.5% and hydroxyl radical scavenging peaked at 97.16% at ASP-W 3%. In summary, ASP-W can improve optical, mechanical, barrier, and thermal stability and antioxidant properties of chitosan film, which provided a certain reference for the development and utilization of polysaccharide in edible packaging film.

Polylactic Acid/Lignin Composites: A Review

With the gradual depletion of petroleum resources and the increasing global awareness of environmental protection, biodegradable plastics are receiving more and more attention as a green substitute for traditional petroleum-based plastics. Poly (lactic acid) is considered to be the most promising biodegradable material because of its excellent biodegradability, biocompatibility, and good processability. However, the brittleness and high cost limit its application in more fields. Lignin, as the second largest renewable biopolymer in nature after cellulose, is not only rich in reserves and low in cost, but it also has an excellent UV barrier, antioxidant activity, and rigidity. The molecular structure of lignin contains a large number of functional groups, which are easy to endow with new functions by chemical modification. Currently, lignin is mostly treated as waste in industry, and the value-added utilization is insufficient. The combination of lignin and poly (lactic acid) can on the one hand solve the problems of the high cost of PLA and less efficient utilization of lignin; on the other hand, the utilization of lignocellulosic biomass in compounding with biodegradable synthetic polymers is expected to afford high-performance wholly green polymer composites. This mini-review summarizes the latest research achievements of poly (lactic acid)/lignin composites. Emphasis was put on the influence of lignin on the mechanical properties of its composite with poly (lactic acid), as well as the compatibility of the two components. Future research on these green composites is also prospected.

Cellulose nanofiber-based pH indicator integrated with resazurin-modified carbon dots for real-time monitoring of food freshness

Modified carbon dots with resazurin (R-CD) were prepared using a hydrothermal method to fabricate a CNF-based pH-responsive indicator for real-time food freshness monitoring. FE-SEM and FTIR results confirmed that the R-CD was uniformly distributed in the CNF matrix. The thermal stability of the CNF/R-CD indicator film was increased, and the water contact angle of the film was slightly lower than that of the neat CNF film. The CNF/R-CD film showed excellent UV-barrier properties, with ∼98.3% and 87.7% blocking the UV-B and UV-A light. The indicator film showed excellent color stability even after 2 months of storage at 25 °C and responded rapidly to alkaline pH and NH3 through a color change from yellow to brownish-red. The CNF/R-CD indicator films exhibited distinct color changes during shrimp packaging depending on pH and TVB-N concentration. Therefore, the CNF/R-CD indicator can be used as a promising pH-sensitive color-changing intelligent packaging application for freshness monitoring.

Simultaneous improvement of the physical and biological properties of starch films by incorporating steviol glycoside-based solid dispersion

Bioactive compounds are frequently incorporated into polysaccharides (e.g., starch) to form active biodegradable films for food packaging, but some of them are water insoluble (e.g., curcumin, CUR) that will make the films have undesirable performance. Herein, CUR was successfully solubilized into the aqueous starch film solution by steviol glycoside (STE, a natural sweetener)-based solid dispersion. The mechanisms of solubilization and film formation were explored through molecular dynamic simulation and various characterization methods. The results showed that the amorphous state of CUR combined with micellar encapsulation of STE achieved the solubilization of CUR. STE and starch chains cooperated to form the film via hydrogen bonding, while CUR was uniformly and densely distributed within the film in the form of needle-like microcrystals. The as-prepared film exhibited high flexibility, great moisture barrier, and excellent UV barrier (UV transmittance: ∼0 %). Compared with the film containing CUR alone, the as-prepared film possessed higher release efficiency, antibacterial activity, and pH response sensitivity due to the assistance of STE. Hence, the introduction of STE-based solid dispersion can simultaneously improve the biological and physical properties of starch films, which provides a green, nontoxic, and facile strategy for the perfect integration of hydrophobic bioactive compounds and polysaccharide-based films.

Production and Characterization of Active Bacterial Cellulose Films Obtained from the Fermentation of Wine Bagasse and Discarded Potatoes by Komagateibacter xylinus.

Potato waste, such as peels, broken or spoiled potatoes and grape bagasse residues from the winery industry, can be used for the biotechnological production of high-value products. In this study, green, sustainable and highly productive technology was developed for the production of antioxidant bacterial cellulose (BC). The aim of this work was to evaluate the feasibility of a low-cost culture medium based on wine bagasse and potato waste to synthesize BC. Results show that the production of BC by Komagateibacter xylinus in the GP culture medium was five-fold higher than that in the control culture medium, reaching 4.0 g/L BC in 6 days. The compounds of the GP culture medium improved BC production yield. The mechanical, permeability, swelling capacity, antioxidant capacity and optical properties of the BC films from the GP medium were determined. The values obtained for the tensile and puncture properties were 22.77 MPa for tensile strength, 1.65% for elongation at break, 910.46 MPa for Young's modulus, 159.31 g for burst strength and 0.70 mm for distance to burst. The obtained films showed lower permeability values (3.40 × 10-12 g/m·s·Pa) than those of other polysaccharide-based films. The BC samples showed an outstanding antioxidant capacity (0.31-1.32 mg GAE/g dried film for total phenolic content, %DPPH• 57.24-78.00% and %ABTS•+ 89.49-86.94%) and excellent UV-barrier capacity with a transmittance range of 0.02-0.38%. Therefore, a new process for the production of BC films with antioxidant properties was successfully developed.

A new water-soluble lignin incorporation enhanced the barrier performance of liquid mulching film

In modern agriculture, the eco-friendly liquid mulching film is a promising alternative to traditional plastic mulching films but challenged by its limited barrier performance. In this work, a facile cyanoethylation technique route was proposed to produce water-soluble lignin from industrial waste lignin, which was further used as a biomimetic bonding adhesive and functional additive to cellulose nanowhisker (CNW) to form the building block of liquid mulching film. It was shown that at low degree of cyanoethylation, the water-solubility was improved through disrupting the strong hydrogen bonding of lignin, while remaining its UV light barrier and antioxidant activity. The well designed liquid mulching film fabricated with cyanoethyl lignin (CEL) coated CNW (CEL@CNW) building block and polyvinyl alcohol (PVA) matrix showed excellent UV barrier (reached ∼ 0 % transmittance at 200 nm with 10 wt% of CEL@CNW) and oxygen barrier ability (oxygen transmission rate reached ∼ 0.12 cm3 m−2 d−1 kPa−1 with 5 wt% of CEL@CNW), which could be used for the protection of photo-sensitive avermectin pesticide against photo-degradation. The real application potential of the fabricated PVA/ CEL@CNW liquid mulching film was verified through the good soil water resistance property and the facilitation of corn seed germination and seedling growth. It was proposed that the CEL incorporation mediated the layered structure of liquid mulching film thus significantly enhancing its overall barrier performance. This work provided a new strategy to valorize industrial waste lignin through water-soluble lignin pursuing, while tailoring a technique platform for the fabrication and application of liquid mulching film toward a more sustainable agriculture.

Performance and Structure Evaluation of Gln-Lys Isopeptide Bond Crosslinked USYK-SPI Bioplastic Film Derived from Discarded Yak Hair.

To reduce the waste from yak hair and introduce resource recycling into the yak-related industry, an eco-friendly yak keratin-based bioplastic film was developed. We employed yak keratin (USYK) from yak hair, soy protein isolate (SPI) from soybean meal as a film-forming agent, transglutaminase (EC 2.3.2.13, TGase) as a catalytic crosslinker, and glycerol as a plasticizer for USYK-SPI bioplastic film production. The structures of the USYK-SPI bioplastic film were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). The mechanical properties, the thermal behavior, light transmittance performance, and water vapor permeability (WVP) were measured. The results revealed that the added SPI possibly acted as a reinforcement. The formation of Gln-Lys isopeptide bonds and hydrophobic interactions led to a stable crosslinking structure of USYK-SPI bioplastic film. The thermal and the mechanical behaviors of the USYK-SPI bioplastic film were improved. The enhanced dispersion and formation of co-continuous protein matrices possibly produced denser networks that limited the diffusion of water vapor and volatile compounds in the USYK-SPI bioplastic films. Moreover, the introduction of SPI prompted the relocation of hydrophobic groups on USYK molecules, which gave the USYK-SPI bioplastic film stronger surface hydrophobicity. The SPI and USYK molecules possess aromatic amino residuals (tyrosine, phenylalanine, tryptophan), which can absorb ultraviolet radiation. Thus, the USYK-SPI bioplastic films were shown to have an excellent UV barrier. The synergy effect between USYK and SPI is not only able to improve rigidity and the application performance of keratin-based composite film but can also reduce the cost of the keratin-based composite film through the low-cost of the SPI alternative which partially replaces the high-cost of keratin. The data obtained from this research can provide basic information for further research and practical applications of USYK-SPI bioplastic films. There is an increasing demand for the novel USYK-SPI bioplastic film in exploit packaging material, biomedical materials, eco-friendly wearable electronics, and humidity sensors.

Poly (lactic acid)-based pH responsive membrane combined with chitosan and alizarin for food packaging

A poly (lactic acid) (PLA) -based functional partition composite membrane (PLA/CA) containing chitosan (CS) and alizarin (AL) was designed by solution casting method. The PLA/CA membrane contains the antibacterial zone of the edge part (PLA/CS) and the pH response detection zone of the central part (PLA/AL). At the same time, the environmentally friendly plasticizer tributyl citrate (TBC) was added to make the prepared PLA/CA composite membrane have good flexibility and high transparency. The results of FE-SEM and FTIR showed that CS and AL were uniformly dispersed in PLA matrix and had good compatibility with PLA. The antioxidant activities of PLA/CS and PLA/AL composite films were 43.3 % and 72.8 %, respectively. At the same time, the inhibitory rates of PLA/CS membrane against Escherichia coli and Staphylococcus aureus were as high as 87.91 % and 75.17 %, respectively. PLA/AL films exhibit excellent UV barrier properties. When the environmental pH (ammonia and acetic acid vapor) changed repeatedly, the PLA/AL membrane showed reversible color change of yellow under acidic condition and purple under alkaline condition. During the packaging and storage of chicken breast meat, the freshness of chicken breast meat can be detected by the color change of functional PLA/CA composite membrane.