Novel procyanidins-loaded chitosan-graft-polyvinyl alcohol film with sustained antibacterial activity for food packaging

Carboxymethyl cellulose-based multifunctional film integrated with polyphenol-rich extract and carbon dots from coffee husk waste for active food packaging applications

Sustainable carboxymethyl cellulose (CMC)-based active composite films were developed through the addition of polyphenol-rich extract from coffee husk (CHE) and carbon dots (CDs) prepared using the biowaste residue of CHE extraction. The influences of various CDs contents on the physicochemical and functional characteristics of composite films have been researched. The 6% (w/w) CHE and 3% (w/w) CDs were uniformly dispersed within the CMC matrix to produce a homogenous film with enhanced mechanical properties. The CMC/CHE/CDs3% film exhibited outstanding UV-light blocking, improved water and gas barriers, potent antioxidant activity with above 95% DPPH and ABTS scavenging rates, and effective antibacterial capabilities against L. monocytogenes and E. coli. The food packaging experiment demonstrated that this active composite film slowed the rotting of fresh-cut apples and extended their shelf-life to 7 days at 4 °C storage. Therefore, the obtained multifunctional film showed promise as an environmentally friendly food packaging material.

Advances in sustainable food packaging applications of chitosan/polyvinyl alcohol blend films

Researchers are addressing environmental concerns related to petroleum-based plastic packaging by exploring biopolymers from natural sources, chemical synthesis, and microbial fermentation. Despite the potential of individual biopolymers, they often exhibit limitations like low water resistance and poor mechanical properties. Blending polymers emerges as a promising strategy to overcome these challenges, creating films with enhanced performance. This review focuses on recent advancements in chitosan/polyvinyl alcohol (PVA) blend food packaging films. It covers molecular structure, properties, strategies for performance improvement, and applications in food preservation. The blend's excellent compatibility and intermolecular interactions make it a promising candidate for biodegradable films. Future research should explore large-scale thermoplastic technologies and investigate the incorporation of additives like natural extracts and nanoparticles to enhance film properties. Chitosan/PVA blend films offer a sustainable alternative to petroleum-based plastic packaging, with potential applications in practical food preservation.

Highly flame retardancy, barrier, mechanical and persistent antibacterial polylactic acid film with high-parallel interconnected thousand layered cake architecture

In this work, a bio-based material (CGP) is obtained by combing chitosan, gelatin and polyvinyl alcohol through a simple solution mixing to simultaneously address polylactic acid film (PLA)' flammability and poor barrier, toughness and antibacterial properties by soaking. The results of open fire testing show that modified PLA films can effectively prolong the combustion time, improve the thermal stability and reduce the release of heat in the cone calorimeter test. For the PLA sample after soaking for 5 times (PLA-5) in particular, it can reduce the peak heat release rate (pHRR) and total heat release (THR) values to 85.8 kW/m2 and 1.3 MJ/m2 from the values of 129.5 kW/m2 and 1.8 MJ/m2 for PLA, respectively. Structural analysis suggests that CGP primarily operates in the condensed phase by forming physical barriers. Meanwhile, the modified PLA films can exhibit superior barrier effects, which indicate the oxygen transmission rate value of PLA-5 decreases to 0.9 cm3/(m2·day) from the 392.5 cm3/(m2·day) of raw PLA film. Moreover, the PLA-5 also have excellent toughness (the value increased to 200.5 % from 31.0 %) and persistent antibacterial effects (it still has 100 % sterilization after 500 days).

PEG-crosslinked O-carboxymethyl chitosan films with degradability and antibacterial activity for food packaging

This study developed a kind of PEG-crosslinked O-carboxymethyl chitosan (O-CMC-PEG) with various PEG content for food packaging. The crosslinking agent of isocyanate-terminated PEG was firstly synthesized by a simple condensation reaction between PEG and excess diisocyanate, then the crosslink between O-carboxymethyl chitosan (O-CMC) and crosslinking agent occurred under mild conditions to produce O-CMC-PEG with a crosslinked structure linked by urea bonds. FT-IR and 1H NMR techniques were utilized to confirm the chemical structures of the crosslinking agent and O-CMC-PEGs. Extensive research was conducted to investigate the impact of the PEG content (or crosslinking degree) on the physicochemical characteristics of the casted O-CMC-PEG films. The results illuminated that crosslinking and components compatibility could improve their tensile features and water vapor barrier performance, while high PEG content played the inverse effects due to the microphase separation between PEG and O-CMC segments. The in vitro degradation rate and water sensitivity primarily depended on the crosslinking degree in comparison with the PEG content. Furthermore, caused by the remaining -NH2 groups of O-CMC, the films demonstrated antibacterial activity against Escherichia coli and Staphylococcus aureus. When the PEG content was 6% (medium crosslinking degree), the prepared O-CMC-PEG-6% film possessed optimal tensile features, high water resistance, appropriate degradation rate, low water vapor transmission rate and fine broad-spectrum antibacterial capacity, manifesting a great potential for application in food packaging to extend the shelf life.

Harnessing the Potential of Chitosan and Its Derivatives for Enhanced Functionalities in Food Applications

As one of the most abundant natural polysaccharides that possess good biological activity, chitosan is extracted from chitin. Its application in the food field is being increasingly valued. However, chitosan extraction is difficult, and its poor solubility limits its application. At present, the extraction methods include the acid-base method, new chemical methods, and biological methods. The extraction rates of chitin/chitosan are 4-55%, 13-14%, and 15-28%, respectively. Different chemical modifications have different effects on chitosan, making it applicable in different fields. This article reviews and compares the extraction and chemical modification methods of chitosan, emphasizing the importance of green extraction methods. Finally, the application prospects of chitosan in the food industry are discussed. This will promote the understanding of the advantages and disadvantages of different extraction methods for chitosan as well as the relationship between modification and application, providing valuable insights for the future development of chitosan.

Synthesis, characterization and application of oligomeric proanthocyanidin-rich dual network hydrogels

A structurally dense hydrogel, with strong hydrogen bonding networks, was formed from poly(vinyl alcohol), sodium alginate, and oligomeric proanthocyanidins, using a combination of freeze-thaw cycles and calcium ion cross-linking. The structure of the hydrogel was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Mechanical testing and thermogravimetric analysis showed that incorporation of proanthocyanidins enhanced both the mechanical properties and the thermal stability of the hydrogel. The hydrogel was also demonstrated to have excellent ultraviolet resistance and antioxidant properties. The hydrogel was further shown that this hydrogel is also capable of generating electrochemical reactions, which strongly suggests that this hydrogel has exciting potential in many fields.

The Preparation and Properties of Amino-Carboxymethyl Chitosan-Based Antibacterial Hydrogel Loaded with ε-Polylysine

In this paper, amino-carboxymethyl chitosan (ACC) was prepared through amino carboxymethylation, which introduces -COOH and -NH2 groups to the chitosan (CS) chains. Meanwhile, dialdehyde starch (DAS) was produced by oxidizing corn starch using sodium periodate. To attain the optimal loading and long-time release of ε-polylysine (ε-PL), the ACC/DAS hydrogels were synthesized through the Schiff base reaction between the amino group on ACC and the aldehyde group in DAS. The molecular structure, microcosmic properties, loading capacity, and bacteriostatic properties of the four types of hydrogels containing different mass concentrations of ACC were investigated. The results showed that the dynamic imine bond C=N existed in the ACC/DAS hydrogels, which proved that the hydrogels were formed by the cross-linking of the Schiff base reaction. With the increasing mass concentration of the ACC, the cross-sectional morphology of the hydrogel became smoother, the thermal stability increased, and the swelling behavior was gradually enhanced. The tight network structure improved the ε-PL loading efficiency, with the highest value of 99.2%. Moreover, the loading of ε-PL gave the hydrogel good antibacterial properties. These results indicate that ACC/DAS hydrogel is potential in food preservation.

One-Pot Preparation of Skin-Inspired Multifunctional Hybrid Hydrogel with Robust Wound Healing Capacity

Bioinspired hydrogels have demonstrated multiple superiorities over traditional wound dressings for wound healing applications. However, the fabrication of bioinspired hydrogel-based wound dressings with desired functionalities always requires multiple successive steps, time-consuming processes, and/or sophisticated protocols, plaguing their clinical applications. Here, a facile one-pot strategy is developed to prepare a skin-inspired multifunctional hydrogel within 30 min by incorporating elastin (an essential functional component of the dermal extracellular matrix), tannic acid, and chitosan into the covalently cross-linked poly(acrylamide) network through noncovalent interactions. The resulting hydrogel exhibits a Young's modulus (ca. 36 kPa) comparable to that of human skin, a high elongation-at-break (ca. 1550%), a satisfactory tensile strength (ca. 61 kPa), and excellent elastic self-restorability, enabling the hydrogel to synchronously and conformally deform with human skin when used as wound dressings. Importantly, the hydrogel displays a self-adhesive property to skin tissues with an appropriate bonding strength (ca. 55 kPa measured on intact porcine skin), endowing the hydrogel with the ability to rapidly self-adhere to intact human skin, sealing the wound surface and also easily being removed without residue left or trauma caused to the skin. The hydrogel also possesses remarkable antibacterial activity, antioxidant capability, and hemocompatibility. All of these collective beneficial properties enable the hydrogel to significantly accelerate the wound healing process, outperforming the commercial wound dressings.

How APTMS Acts as a Bridge to Enhance the Compatibility of the Interface between the Hydrophilic Poly(vinyl alcohol) Film and the Hydrophobic Stearic Acid Coating

The hydrophobic modification of poly(vinyl alcohol) (PVA) film as a biodegradable packaging material has received significant attention in recent research. Despite the use of stearic acid (SA) as a coating for the PVA film, a challenge persists due to the poor compatibility between SA and PVA. This study addressed the aforementioned issue by utilizing (3-aminopropyl)trimethoxysilane (APTMS) as a bridging agent to establish a connection between the hydrophilic PVA film and the hydrophobic SA coating through hydrogen bonding and chemical reactions. First, SEM and EDS analyses confirmed the enhanced interfacial compatibility between the SA coating and the PVA film. Subsequently, the results from 1H NMR, FTIR, and XPS experiments presented evidence of hydrogen bonding and chemical reactions among APTMS, SA, and the PVA film. Interestingly, the PVA-APTMS-SA film demonstrated a contact angle of 120.77°, a water absorption of 7.81%, and a water vapor transmission rate of 8.69 g/m2/h. Furthermore, such a composite film displayed exceptional adhesion performance, requiring detachment stresses of 9.86 ± 0.91 and 6.17 ± 0.75 MPa when tested on glass and marble surfaces, respectively. In conclusion, the PVA-APTMS-SA film exhibited significant potential in extending the freshness of fresh-cut apples, making it a promising eco-friendly packaging material for food preservation.

Nano Ag/PPy Biocomposites Based on Graphene Oxide Modified Bacterial Cellulose from the Juice of Xinhui Citrus and Its Antibacterial Activity

Bacterial cellulose (BC) is a green, natural biopolymer with excellent biocompatibility and a film-forming ability. However, its lack of inherent antibacterial activity restricts its application in medical materials and food preservation. In this study, BC derived from the juice of discarded Xinhui citrus was obtained through fermentation and further modified in situ with graphene oxide (GO) to obtain BC(GO). Subsequently, BC(GO) was loaded with cell-compatible polypyrrole (PPy) and antibacterial agent silver nanoparticles (AgNPs) to prepare Ag-PPy/BC(GO) composite films. Composite films were characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) to evaluate their chemical structure and morphology. The results demonstrate effective adsorption of PPy and AgNPs onto the surface of BC nanofibers modified with GO. Antibacterial experiments reveal synergistic antibacterial effects of PPy and AgNPs. The Ag-PPy/BC(GO) membranes exhibit strong antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), with 48-h growth inhibition rates of 75-84% and 82-84%, respectively.

Biobased Intelligent Food-Packaging Materials with Sustained-Release Antibacterial and Real-Time Monitoring Ability

It has been widely accepted that sustainable polymers derived from renewable resources are able to replace the short-turnover petroleum-based materials and reduce environmental impact in the future. However, their hydrophilic chemical structures rich with oxygen groups could lead to easy growth of bacteria, which greatly limit their applications in packaging materials. Here, we present an intelligent food-packaging material with sustained-release antibacterial and real-time monitoring ability based on totally biobased contents. In detail, sodium alginate with Artemisia argyi emission oil (encapsulated in gelatin-Arabic gum microcapsules) and citric acid-sourced pH-responsive carbon quantum dots (CQDs) are coated on bamboo cellulose papers. The obtained biobased composite material (almost 100% biocarbon content) with antibacterial ability is able to extend the shelf life of fresh shrimps and can be biodegraded. Moreover, owing to the introduction of CQDs, the composite can rapidly (within 1 s) detect slight pH variations (response pH ∼5, 10-9 mol/L of OH-) through an obvious color change (hue value from 305 to 355°). The developed strategy may open up new opportunities in the design of multifunctional biobased composites for intelligent applications.

Amino carboxymethyl chitosan//dialdehyde starch/polyvinyl alcohol double-layer film loaded with ε-polylysine

To develop food packaging with good antibacterial activity and mechanical performance, four amino carboxymethyl chitosan (ACC)//dialdehyde starch (DAS) /polyvinyl alcohol (PVA) films were prepared by Schiff base and hydrogen bond interactions for efficient loading and release of ε-polylysine (ε-PL). The effects of the Schiff base reaction on the physicochemical properties of the films were explored based on the different aldehyde group contents in DAS. The ACC//DAS₄/PVA film exhibited a tensile strength of 62.5 MPa, and the water vapor and oxygen permeability was 8.77 × 10^-3·g·mm/m²·d·kPa and 0.15 × 10³·cm³·mm/m²·d, respectively. By leveraging the Schiff base reaction, the film swelling properties were improved by adjusting the cross-link density, mesh size, and molecular mass between the cross-links. The ACC//DAS₄/PVA film could efficiently load ε-PL with a value of 98.44% and long-term release in a food simulant of 10% ethanol at 25 °C for 120 min. Moreover, the ACC-ε-PL//DAS₄/PVA film was successfully used for salmon preservation.

Alginate/Pectin Film Containing Extracts Isolated from Cranberry Pomace and Grape Seeds for the Preservation of Herring

Alginate/pectin films supplemented with extracts from cranberry pomace (CE) or grape seeds (GE) were developed and applied to herring fillets that were stored for 18 days at 4 °C. Herring coated with films containing GE and CE inhibited the growth of Listeria monocytogenes and Pseudomonas aeruginosa during the storage period, whereas pure alginate/pectin films did not show an antimicrobial effect against the tested pathogens. The application of alginate/pectin films with CE and GE minimised pH changes and inhibited total volatile basic nitrogen (TVN) and the formation of thiobarbituric acid-reactive substances (TBARS) in the herring fillets. The coating of herring fillets with films with CE or GE resulted in three- and six-fold lower histamine formation and one-and-a-half- and two-fold lower cadaverine formation, respectively, when compared to unwrapped herring samples after 18 days of storage. The incorporation of 5% extracts isolated from cranberry pomace or grape seeds into the alginate/pectin film hindered herring spoilage due to the antimicrobial and antioxidant activity of the extracts.

Turmeric carbon quantum dots enhanced chitosan nanocomposite films based on photodynamic inactivation technology for antibacterial food packaging

The increased demand for food quality and safety has led the food industry to pay urgent attention to new packaging materials with antimicrobial activity. In this study, we combined photodynamic inactivation of bactericidal technology in food packaging materials by incorporating fluorescent carbon quantum dots (CDs) prepared from the natural plant turmeric into a chitosan matrix to prepare a series of active composite food packaging films (CDs-CS). The chitosan film containing CDs had better mechanical properties, UV protection and hydrophobicity. Under irradiation with a 405 nm light source, the composite film was able to produce abundant reactive oxygen species, and the CDs-CS₂ film exhibited reductions of approximately 3.19 and 2.05 Log₁₀ CFU/mL for Staphylococcus aureus and Escherichia coli respectively within 40 min. In cold pork storage applications, CDs-CS₂ films showed inhibition of the growth of colonization in pork and retarded the spoilage of pork within 10 days. This work will provide new insights to explore safe and efficient antimicrobial food packaging.

Polypropylene composite hernia mesh with anti-adhesion layer composed of PVA hydrogel and liposomes drug delivery system

Polypropylene (PP) mesh has been widely used in hernia repair as prosthesis material owing to its excellent balanced biocompatibility and mechanical properties. However, abdominal adhesion between the visceral and PP mesh is still a major problem. Therefore, anti-adhesive PP mesh was designed with poly(vinyl alcohol) (PVA) hydrogel and liposomes drug delivery system. First, PVA hydrogel coating was formed on the surface of PP mesh with freezing-thawing processing cycles (FTP). Subsequently, the lyophilized PVA₁₀-c-PP was immersed in rapamycin (RPM)-loaded liposome solution until swelling equilibrated to obtain the anti-adhesion mesh RPM@LPS/PVA₁₀-c-PP. It was demonstrated that the hydrogel coating can stably fix on the surface of PP mesh even after immersed in PBS solution at 37 °C or 40 °C for up to 30 days. In vitro cell tests revealed the excellent cytocompatibility and the potential to inhibit cell adhesion of the modified PP mesh. Moreover, the anti-adhesive effects of the RPM@LPS/PVA₁₀-c-PP mesh was evaluated through in vivo experiments. The RPM@LPS/PVA₁₀-c-PP mesh exhibited less adhesion than original PP mesh throughout the duration of implantation. At 30 days, the adhesion score of RPM@LPS/PVA₁₀-c-PP mesh was 1.37 ± 0.75, however the original PP was 3 ± 0.71. Furthermore, the results of H&E and Masson trichrome staining proved that the RPM@LPS/PVA₁₀-c-PP mesh showed slighter inflammation response and significant looser fibrous tissue surrounded the PP filaments as compared to the native PP. The current findings manifested that this type of RPM@LPS/PVA₁₀-c-PP might be a potential candidate for anti-adhesion treatment. DATA AVAILABILITY: Data will be made available on request.

Improved hydrophobicity, antibacterial and mechanical properties of polyvinyl alcohol/quaternary chitosan composite films for antibacterial packaging

Polyvinyl alcohol (PVA) and chitosan (CS) are attractive polymeric feedstocks for developing eco-environmental materials. In this work, a biodegradable and antibacterial film was developed based on PVA blending with different long-chain alkyl and different contents of quaternary chitosan through solution casting, in which quaternary chitosan not only acted as an antibacterial agent but also improved hydrophobicity and mechanical properties. A novel peak appeared at 1470 cm^-1 in Transform Infrared Spectroscopy (FTIR) and a new CCl bond spectral peak at 200 eV in X-ray photoelectron spectroscopy (XPS) spectra suggested that CS was successfully modified by quaternary. Besides, the modified films have better antibacterial effects against Escherichia (E. coli) and Staphylococcus (S. aureus) and present stronger antioxidant properties. Optical properties demonstrated that the light transmittance on both UV and visible light showed a decreasing trend with the increase of the quaternary chitosan contents. Whereas the composite films have enhanced hydrophobicity than PVA film. Furthermore, the composite films had higher mechanical properties, in which Young's modulus, tensile strength, and elongation at break were 344.99 MPa, 39.12 MPa, and 507.09 %, respectively. This research demonstrated that the modified composite films could extend the shelf of life on antibacterial packaging.

Preparation of Novel Composites of Polyvinyl Alcohol Containing Hesperidin Loaded ZnO Nanoparticles and Determination of Their Biological and Thermal Properties

Hesperidin (HSP) is considered to be the most effective antimicrobial agent against SARS-CoV2 virus. The HSP was loaded onto ZnO nanoparticles that were successfully incorporated, via the hydrothermal method, into polyvinyl alcohol (PVA) for use as food packaging material. The hydrothermal method enabled the bioactive ZnO-HSP to be homogeneously dispersed in the PVA, which significantly increased the thermal stability of the matrix, while decreasing the softening temperature. The water holding capacity and water solubility of the obtained nanocomposites was reduced compared to the PVA. Finally, the ZnO-HSP antimicrobial agent contributed important antibacterial properties to the PVA and increased its antioxidant capacity against Staphylococcus aureus and Escherichia coli pathogens. In addition, the nanocomposites had no cytotoxic/proliferative effects on cancer cells. All results showed promise that the PVA/ZnO-HSP nanocomposites would be an excellent alternative for food packaging applications.

Chitosan-Based Edible Coatings Containing Essential Oils to Preserve the Shelf Life and Postharvest Quality Parameters of Organic Strawberries and Apples during Cold Storage

Edible coatings and films have been researched for more than three decades due to their ability to be incorporated with different functional ingredients or compounds as an option to maintain the postharvest quality of fruits and vegetables. The aim of this study was to evaluate the effect of three types of chitosan-based (CH) edible coatings obtained from medium and high molecular weight chitosan, containing ascorbic or acetic acid and sea buckthorn or grape seed essential oils on the physical-chemical and microbiological properties of organic strawberries and apple slices during cold storage at 4 °C and 8 °C. Scanning electron microscope images showed both a smooth structure and a fracture and pore structure on strawberry coatings and a dense and smooth structure on the apple slices coatings. Further, the edible coatings managed to reduce the microbial load of yeasts and molds of the coated strawberries during the storage period. Overall, the treatments preserved the ascorbic acid, total polyphenol content, and antioxidant activity for all the tested samples compared to the control sample, throughout the storage period. In addition, the water activity (a_w) of the coated samples presented lower values (0.96-0.98) than the control samples. The obtained results indicate that the developed chitosan-based edible coatings could maintain the postharvest parameters of the tested samples, also leading to their shelf-life prolongation.

Quality Changes in Black Chokeberry Juice Treated by Thermal-Assisted High Hydrostatic Pressure during Cold Storage

The effects of thermal-assisted high hydrostatic pressure (TAHHP), high hydrostatic pressure (HHP), and thermal pasteurization (TP) treatments on the quality of aronia juice were evaluated in this study. The results showed that TAHHP and HHP significantly decreased the aerobic plate counts of aronia juice. No significant differences in terms of physicochemical properties, such as pH and total soluble solids, were observed between aronia juice treated with high pressure or thermal pasteurization treatment after 28 days of storage. TAHHP and HHP affected the colour and antioxidant characteristics of aronia juice, though to a significantly lower extent than TP. This result demonstrates that TAHHP and HHP can better maintain the original quality of aronia juice than TP. In summary, both TAHHP and HHP can maintain the microbiological safety and original quality characteristics of aronia juice. TAHHP can effectively increase the safety and duration of cold storage of aronia juice, and hence is highly useful for the juice industry.

Ferulic acid- and gallic ester-acylated pectin: Preparation and characterization

In this study, pectin was modified with ferulic acid (Fa), trans-ferulic acid (trans-Fa), methyl gallate (MG), and ethyl gallate (EG) via the enzymatic method using aqueous/organic phases to enhance its physiochemical and bio-active properties. Results revealed that lipase might catalyze the hydrolysis of the ester bond within pectin in aqueous phase and prompt the transesterification between the hydroxyl group in the para position in Fa/trans-Fa or the 2'-OH group of MG/EG and the carboxylic group of pectin in the organic phase. The graft ratio was 21.00%, 21.67%, 13.24%, and 11.93% for the Fa-, trans-Fa-, MG-, and EG-modified pectin, respectively. In addition, compared with native pectin, the modified pectin exhibited improved apparent viscosity and emulsion activity. Moreover, the clearance of 1,1-diphenyl-2-picryl hydrazine (DPPH) and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) was effectively enhanced for the modified pectin. Furthermore, the modified pectin exhibited strong antibacterial activity against Escherichia coli and Staphylococcus aureus while no cytotoxic effects based on the results of cell culture experiments. Our results provide a theoretical basis for the expansion of pectin applications in the food and pharmaceutical industries.

Condensed Tannins, a Viable Solution To Meet the Need for Sustainable and Effective Multifunctionality in Food Packaging: Structure, Sources, and Properties

Condensed tannins (CT) have been the focus of increasing interest in the last years as a result of their potent biological properties, which have prompted their use in the food and feed sector as functional ingredients. The possible exploitation of these compounds as multifunctional additives for the implementation of active food packaging has also been recently appreciated. In this perspective, an overview of the structural features, accessible sources, methods of analysis, and functional properties of CT is provided, with the aim of critically emphasizing the opportunities offered by this widespread class of natural phenolic compounds for the rational design of multifunctional and sustainable food packaging materials.

Novel application of ion exchange membranes for preparing effective silver and copper based antibacterial membranes

Ion exchange membranes (IEMs) are widely used in water treatment applications such as electrodialysis. However, the exploration of IEMs as effective antibacterial food contact materials (e.g., food packaging membranes) against pathogenic bacteria to ensure food safety has not been reported. Here, we report a simple but effective method to prepare high performance antibacterial membranes via ion exchange coupled with in-situ reduction. The general membrane properties are characterized using SEM, EDS, FTIR, XPS, XRD, DSC, TGA, water uptake, etc. The distribution of silver and copper in the membranes are generally in line with the distribution of sulfur, indicating that the antibacterial ions are introduced into the membranes via ion exchange and are bonded with the sulfonate groups in the membranes. The antibacterial performance is investigated using zone of inhibition tests and continuous bacteria growth inhibition tests. All of the prepared membranes show obvious antibacterial activities compared to the bare cation exchange membranes. The diameters of inhibition zone against Staphylococcus aureus (S. aureus) are all larger than those of Escherichia coli (E. coli), indicating that the prepared membranes are more efficient in inhibiting S. aureus compared to E. coli. Furthermore, the silver-based membrane shows more sustainable antibacterial activities compared to the copper-based membrane. Especially, the results clearly reveal that the silver-based membrane is capable of killing bacteria instead of just inhibiting the growth of bacteria. We have shown for the first time that membranes derived from IEMs have the potential as food contact materials to inhibit the growth of pathogenic bacteria so as to eliminate the risk of bacterial infections and meanwhile delay food spoilage due to bacteria growth.

Preparation and Characterization of Chitosan-Nano-ZnO Composite Films for Preservation of Cherry Tomatoes

Chitosan is widely used as a natural preservative of fruits and vegetables, but its poor mechanical and water resistances have limited its application. Therefore, in this study, we prepared chitosan composite films by incorporating different amounts of nano-zinc oxide (nano-ZnO) to improve the mechanical properties of chitosan. We also assessed the antibacterial activity of these films against selected microorganisms. The addition of nano-ZnO improved the tensile strength (TS) and elongation at break (EAB) of the chitosan films and reduced their light transmittance. TS and EAB increased from 44.64 ± 1.49 MPa and 5.09 ± 0.38% for pure chitosan film to 46.79 ± 1.65 MPa and 12.26 ± 0.41% for a 0.6% nano-ZnO composite film, respectively. The ultraviolet light transmittance of composite films containing 0.2%, 0.4%, and 0.6% nano-ZnO at 600 nm decreased from 88.2% to 86.0%, 82.7%, and 81.8%, respectively. A disc diffusion test showed that the composite film containing 0.6% nano-ZnO had the strongest antibacterial activity against Alicyclobacillus acidoterrestris, Staphylococcus aureus, Escherichia coli, and Salmonella. In a 15-day preservation study, chitosan composite films containing 0.6% nano-ZnO maintained the soluble solid content of cherry tomatoes, effectively inhibited their respiration, and exhibited good antibacterial properties against the selected microorganisms. Overall, the prepared chitosan nano-ZnO composite film showed a good preservation effect on cherry tomatoes.