Bio-based antibacterial food packaging films and coatings containing cinnamaldehyde: A review.

As a typical bioactive compound from the bark and leaves of the trees of the genus Cinnamomum, cinnamaldehyde (CIN) is natural and safe. Its excellent antibacterial activity against various foodborne microorganisms is growingly regarded as a promising additive for improving and enhancing the properties of bio-based packaging films/coatings. This review systematically summarized the bio-based food packaging films/coatings containing CIN developed recently. The effects of CIN incorporation on physical and chemical properties of the antibacterial food packaging films/coatings, including thickness, color index, transparency, water content, water solubility, water contact angle, mechanical performances, water barrier performances, and antibacterial performances, were discussed. Simultaneously, this work also concluded that an explanation of the antibacterial mechanism of CIN and preparation methods of bio-based packaging films/coatings containing CIN/CIN carriers. Notably, the incorporation of CIN into the films/coatings could enhance their antibacterial performance extend the shelf-life of various foods, such as fish, meats, vegetables, fruits, and other perishable food, while improving their physical and chemical properties. Although incorporating CIN into food packaging films/coatings has been extensively studied, long-term follow-up research on the human safety of active food packaging films/coatings containing CIN needs to be carried out.

Insights into electrospun pullulan-carboxymethyl chitosan/PEO core-shell nanofibers loaded with nanogels for food antibacterial packaging.

Nisin, a natural substance from Lactococcus lactis, displays a promising antibacterial ability against the gram-positive bacteria. However, it is susceptible to the external environment, i.e. temperature, pH, and food composition. In this study, a dual stabilization method, coaxial electrospinning, was applied to protect nisin in food packaging materials and the effect of nisin concentration on the properties of the nanofibers was investigated. The core-shell nanofibers with pullulan as a core layer and carboxymethyl chitosan (CMCS)/polyethylene oxide (PEO) as shell layer were prepared, and then the prepared CMCS-nisin nanogels (CNNGs) using a self-assembly method were loaded into the core layer of the nanofibers as antibacterial agents. The result revealed that the smooth surface can be observed on the nanofibers by microstructure characterization. The CNNGs-loaded nanofibers exhibited enhanced thermal stability and mechanical strength, as well as excellent antibacterial activity. Importantly, the as-formed nanofibers were applied to preserve bass fish and found that the shelf life of bass fish packed by CNNGSs with nisin at a concentration of 8 mg/mL was effectively extended from 9 days to 15 days. Taken together, the CNNGs can be well stabilized with the core-shell nanofibers, thus exerting significantly improved antimicrobial stability and bioactivity. This special structure exerts a great potential for application as food packaging materials to preserve aquatic products.

Highly Stretchable, Transparent, and Adhesive Double-Network Hydrogel Dressings Tailored with Fish Gelatin and Glycyrrhizic Acid for Wound Healing.

It remains challenging to fabricate highly stretchable and adhesive hydrogel dressings for wound healing using simple, safe, and green methods. Herein, inspired by the main components of snail mucus, a fully physical double-network (DN) hydrogel dressing composed of fish gelatin (FGel) and glycyrrhizic acid (GL) was fabricated, in which FGel provided a protein scaffold to mimic snail mucus proteins, while GL mimicked the adhesion and bioactivity of snail mucus because of its abundant carboxyl and hydroxyl groups and intrinsic immunomodulatory activity. As expected, the obtained FGel/GL hydrogel dressings exhibited outstanding mechanical and adhesive performances (flexibility, stretchability, adhesive ability, and removability), high transparency, and good antifreezing properties. More importantly, they also possessed excellent biocompatibility, cell migration, and angiogenesis ability in vitro experiments. Finally, animal experiments in vivo indicated that the FGel/GL hydrogel dressings significantly promoted full-thickness wound healing, including promoting granulation tissue formation, collagen deposition, and skin angiogenesis and inhibiting the inflammatory response. All these findings indicated that the FGel/GL hydrogel dressings have great potential for applications in the clinical treatment of wound healing.

Preparation, characterization and biological activity of phosphorylated surface deacetylated chitin nanofibers.

Phosphorylation is a key route to achieve varieties of biological activities for polysaccharides. Here, we report the phosphorylated surface deacetylated chitin nanofibers (PS-ChNFs) using the sodium tripolyphosphate/sodium trimetaphosphate (STPP/STMP) method. Response surface methodology (RSM) was employed to optimize in this study. Under optimal conditions, a maximum degree of substitution (DS) of 0.13 was obtained. In addition, the structures of PS-ChNFs were investigated by Fourier transform infrared spectroscopy (FT-IR), Nuclear Magnetic Resonance spectra (NMR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM) and (Energy Dispersive Spectroscopy-mapping) EDS-mapping. The findings revealed that the FT-IR spectroscopy and XPS analysis confirmed the appearance of phosphate groups in PS-ChNFs. The 31P NMR results indicate that the PS-ChNFs structure has characteristic peaks of P elements. SEM images showed that PS-ChNFs had a rough surface with many cavities, but the P elements on the surface of the EDS-mapping are uniformly distributed throughout the sample without any enrichment. Antioxidant and antibacterial test showed that PS-ChNFs had significant scavenging effect on free radicals and antibacterial effect. The above results indicate that the chemical modification of PS-ChNFs was successful.

Microencapsulation of Carvacrol by Complex Coacervation of Walnut Meal Protein Isolate and Gum Arabic: Preparation, Characterization and Bio-Functional Activity.

As a natural phenolic compound, carvacrol has attracted much attention due to its excellent antibacterial and antioxidant activities. However, its application is limited due to its instability, such as easy volatilization, easy oxidation, etc. Protein-polysaccharide interactions provide strategies for improving their stability issues. In this study, the plant-based carvacrol microcapsules via complex coacervation between walnut meal protein isolate (WMPI) and gum Arabic (GA) has been fabricated and characterized. The formation conditions of WMPI-GA coacervates were determined by some parameters, such as pH, zeta-potential, and turbidity. The optimum preparation conditions were achieved at pH 4.0 with a WMPI-to-GA ratio of 6:1 (w/w). The mean particle size, loading capacity (LC), and encapsulation efficiency (EE) of the microcapsules were 43.21 µm, 26.37%, and 89.87%, respectively. Fourier transform infrared spectroscopy (FT-IR) and fluorescence microscopy further confirmed the successful microencapsulation of carvacrol. The microencapsulation of carvacrol improved the thermal stability of the free carvacrol. The swelling capacity results indicated that it could resist gastric acid, and facilitate its intestinal absorption. Meanwhile, the carvacrol molecules trapped within the microcapsules could be continuously released in a concentration-dependent manner. Furthermore, the microcapsules presented good antioxidant activity and antibacterial activity against the Gram-negative (E. coli) and the Gram-positive (S. aureus) bacteria. These results indicated that the obtained carvacrol microcapsules have a potential application value as a food preservative in the food industry.

Immobilization of phlorotannins on nanochitin: A novel biopreservative for refrigerated sea bass (Lateolabrax japonicus) fillets.

A novel biopreservative was developed by immobilizing phlorotannins into nanochitin (NCh). NCh were selected as a host complex to immobilized phlorotannins and the structural properties and antioxidant activity of the NCh-phlorotannins nanocomplex was investigated. The NCh-phlorotannins showed high antioxidant activity, as evidenced by free radical scavenging activity test. Moreover, the effects of NCh-phlorotannins on physical [color, water holding capacity (WHC), and texture], chemical [thiobarbituric acid (TBA) values, total volatile base nitrogen (TVB-N), and pH], microbiological [total viable count], changes of refrigerated sea bass (Lateolabrax japonicus) fillets were also evaluated. Sea bass fillets add with 1.5 g/kg NCh-phlorotannins had lower bacterial growth, pH, TVB-N and TBA as well as better characteristics of texture, color, and WHC than those of the control group during refrigerated storage. The efficiency of NCh-phlorotannins treatment was also better than that of phlorotannins or NCh treatment alone. Therefore, NCh-phlorotannins may be a potential biopreservative to extend the shelf-life of sea bass fillets quality during refrigerated storage.

Construction of carboxymethyl konjac glucomannan/chitosan complex nanogels as potential delivery vehicles for curcumin.

Construction of nanoscale delivery systems from natural food biopolymer complexes have attracted increasing interests in the fields of food industries. In this study, novel carboxymethyl konjac glucomannan/ chitosan (CMKGM/CS) nanogels with and without 1-ethyl-3-(3-dimethylaminopropyl) /N-hydroxysuccinimide) (EDC/NHS)-initiated crosslinking were prepared. The physicochemical and structural properties of the CMKGM/CS nanogels and their potential to be a delivery vehicle for curcumin were investigated. Compared to original uncrosslinked nanogels, crosslinking did not alter particle size and morphology but decreased zeta potential of nanogels. Fourier transform infrared spectrum confirmed that the amide linkage was formed between CMKGM and CS, which obviously enhanced the stability of crosslinked nanogels under gastrointestinal conditions. Furthermore, the crosslinked nanogels not only had higher encapsulation efficiency of curcumin but also better sustained release behavior under simulated gastrointestinal conditions. These findings suggested that the crosslinked CMKGM/CS nanogels might be a promising delivery system for nutrients.

Investigation of the structural and physical properties, antioxidant and antimicrobial activity of konjac glucomannan/cellulose nanocrystal bionanocomposite films incorporated with phlorotannin from Sargassum.

In this study, environmentally friendly bionanocomposite films were prepared by incorporating phlorotannins from Sargassum (PS) into konjac glucomannan (KGM)/cotton cellulose nanocrystals (CNC) composites. The effects of different concentrations of PS (5%, 9%, 13%, and 17%, w/w) on the microstructure, physical properties, antioxidant and antibacterial activities of the resultant bionanocomposite films were evaluated. The results of scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectra showed that PS was well compatible with the KGM/CNC composites matrix, which led to form a compact and uniform structure of the films. Thermogravimetric analysis and differential scanning calorimetry demonstrated that incorporating PS improved the heat stability of KGM/CNC bionanocomposite films. And addition of the appropriate amount of PS improved the mechanical and water-vapor barrier-related properties of the bionanocomposite film. For instance, with 9% PS, the tensile strength of the KGM/CNC/PS bionanocomposite film increased by 33.9%, and the water-vapor transmittance decreased by 41.67% compared to that of the KGM/CNC films. Moreover, the addition of PS endowed the KGM/CNC film with excellent antioxidant and antibacterial properties. Therefore, KGM/CNC/PS bionanocomposite films have great potential to be applicated as active packaging in the food packaging industry.

Development and characterization of electrospun nanofibers based on pullulan/chitin nanofibers containing curcumin and anthocyanins for active-intelligent food packaging.

An electrospun nanofiber based on pullulan/chitin nanofibers (PCN) containing curcumin (CR) and anthocyanins (ATH) was developed using an electrospinning technique for active-intelligent food packaging. The results of scanning electron microscopy and attenuated total reflection Fourier transform infrared spectroscopy indicated that CR and ATH were successfully immobilized on the film-forming substrate based on PCN. The physical and chemical properties of nanofibers with no colorant, a single colorant, and double colorants were compared. The nanofiber containing ATH and CR (PCN/CR/ATH) had stronger antioxidant and antimicrobial activities than those of nanofibers containing CR (PCN/CR) or ATH (PCN/ATH). With respect to pH sensitivity, the color of the PCN/CR nanofibers did not change obviously, but the color of the PCN/ATH and PCN/CR/ATH nanofibers changed significantly with the change in pH. Furthermore, the PCN/CR/ATH nanofibers clearly changed color with the progressive spoilage of Plectorhynchus cinctus at room temperature. Therefore, the electrospun PCN/CR/ATH nanofiber have great application potential in active-intelligent food packaging.

Preparation and characterization of citric acid crosslinked konjac glucomannan/surface deacetylated chitin nanofibers bionanocomposite film.

Novel bionanocomposite films were prepared by combining konjac glucomannan/surface deacetylated chitin nanofibers (KGM/S-ChNFs) with different concentrations of citric acid (CA) (10%-25%) via a solution casting method. The effect of CA-induced crosslinking on the rheological behavior of film-forming solutions (FFS) as well as the structural and physicochemical properties of the resulting bionanocomposite films were evaluated. The results revealed that the increased CA loadings increased the shear viscosity of FFS. Fourier transform infrared spectra and scanning electron microscopy results confirmed the successful crosslinking between CA and S-ChNFs. The addition of 20 wt% CA was defined as the optimal condition, resulting in minimum water sensitivity and permeability, while maintaining a good combination of tensile strength and antimicrobial properties. This work supported the conclusion that CA crosslinking was an effective pathway for the preparation of polysaccharide-based bionanocomposite films with improved properties, which may be a promising material for active food packaging applications.

Effect of carboxylation cellulose nanocrystal and grape peel extracts on the physical, mechanical and antioxidant properties of konjac glucomannan films.

Active bionanocomposite films were prepared by incorporating konjac glucomannan (KGM) as a matrix, with carboxylation cellulose nanocrystal (C-CNC) as a reinforcement agent and grape peel extracts (GPE) as a natural antioxidation agent. The effects of C-CNC and/or GPE addition on the structural, morphological, barrier, thermal, mechanical and antioxidant properties of the bionanocomposite films were investigated. The rheological results of film forming solutions revealed that C-CNC and GPE were well dispersed in the KGM matrix. Scanning electron micrographs observed the addition of C-CNC had little effect on the microstructure, while more roughness and unevenness were observed on the film surface and cross-section with the C-CNC and GPE. Furthermore, the water vapor barrier property and transparency of the films improved by the addition of the C-CNC and GPE. Notably, the incorporating of C-CNC or GPE significantly alter the mechanical of the KGM/C-CNC/GPE bionanocomposite films. The highest tensile strength was achieved for the KGM/GPE bionanocomposite film with 10 wt% C-CNC, indicating C-CNC and GPE had synergistic effect on enhancing the TS of KGM film. Moreover, the KGM/C-CNC/GPE films exhibited strong antioxidant activity. These results suggested that KGM/C-CNC/GPE bionanocomposite films can be used as an active food packaging for increasing shelf life of packaged foods.

In situ self-assembly chitosan/ε-polylysine bionanocomposite film with enhanced antimicrobial properties for food packaging.

A set of chitosan/ε-polylysine (ε-PL) bionanocomposite films were prepared by a simple in situ self-assembly technique using sodium tripolyphosphate (TPP) as cross-linking agent. The physical, mechanical, structural, and antimicrobial properties of these films were investigated. Fourier infrared spectroscopy and X-ray diffraction showed that the introduction of TPP promoted the formation of hydrogen bonds and electrostatic interactions among functional groups of chitosan or ε-PL, which improved the tensile strength and decreased the water solubility, water vapor permeability and surface wettability of films. On the other hand, the incorporation of ε-PL weakened the bionanocomposite film' structure and integrity, resulting in a decrease trend of films' mechanical and barrier properties. More importantly, the bionanocomposite films exhibited excellent antimicrobial efficacy against E. coli and S. aureus by the increasing ratio of ε-PL. And ε-PL presented a sustained release from the films, which was closely related to TPP concentration. Results of this study suggested that chitosan/ε-PL films could be used as antimicrobial bio-material and have great potential in food industry.

Preparation of an intelligent film based on chitosan/oxidized chitin nanocrystals incorporating black rice bran anthocyanins for seafood spoilage monitoring.

A novel intelligent film was developed by immobilizing 1%, 3% and 5% black rice bran anthocyanins (BACNs) into oxidized-chitin nanocrystals (O-ChNCs)/ chitosan (CS) matrix. The ultraviolet-visible spectrum of BACNs solutions showed color variations from red to greyish green in a range of pH 2.0-12.0. Fourier transform infrared spectrum and atomic force microscope of the films showed that O-ChNC and BACNs were well dispersed into the CS matrix. Although the incorporation of BACNs decreased the mechanical and barrier properties of the CS/O-ChNCs/BACNs (COB) films, it endowed the COB films with excellent UV-barrier, antioxidant and pH sensitivity character. The results of the application trial showed that the COB films containing 3% of BACNs (COB-3) were able to monitor the spoiling of fish and shrimp by visible color changes. Therefore, the developed COB-3 films could be used as an intelligent food packaging for monitoring animal-based protein food spoilage.

Transparent bionanocomposite films based on konjac glucomannan, chitosan, and TEMPO-oxidized chitin nanocrystals with enhanced mechanical and barrier properties.

The development of biopolymer-based films for food packaging is increasing owing to their environmental appeal, renewability, and biodegradability. In this study, transparent and biodegradable konjac glucomannan (KGM)/chitosan (CS)/TEMPO-oxidized chitin nanocrystal (TEMPO-ChNCs) bionanocomposite films were prepared. The TEMPO-ChNCs were prepared from chitin using the 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO) oxidation method and were used as a reinforcement nanofiller for the bionanocomposite films. The effect of TEMPO-ChNCs content on both rheological properties of film-forming solutions (FFS) and structural and physical properties of the resultant films was investigated. The rheological results of the FFS revealed that the TEMPO-ChNCs interacted with KGM and CS through electrostatic interaction and the hydrogen bonds in the bionanocomposite matrix, which was in agreement with the Fourier transform infrared spectroscopy and X-ray diffraction results. The microstructure of the films showed that 3% (w/w) TEMPO-ChNCs were homogeneously dispersed within the KGM/CS matrix, reducing the free volume of the biocomposite matrix and improving the final film mechanical and barrier properties (P < 0.05). Furthermore, these bionanocomposite films exhibited good thermal stability. The incorporation of TEMPO-ChNCs in the KGM/CS matrix produced flexible and transparent bionanocomposite films. Thus, this bionanocomposite films has potential use in food packaging applications.

Development of antimicrobial packaging materials by incorporation of gallic acid into Ca2+ crosslinking konjac glucomannan/gellan gum films.

Antibacterial films were prepared by incorporating konjac glucomannan (KGM) and gellan gum (GG) as a matrix, glycerin as a plasticizer, CaCl2 as a cross-linking agent, and gallic acid as a natural antibacterial agent. Structure was analyzed by using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Thermal stability of the blends was higher than pure GG, due to Ca2+ crosslinking between GG and KGM. Water contact angle and water vapor permeability were analyzed to determine hydrophobicity of films. Morphological studies revealed that surface compactness and homogeneity of blended films increased with KGM content. The addition of KGM improved the mechanical strength of films significantly. Moreover, KGM improved the release capacity of the blended films, while enhancing antimicrobial activity against Escherichia coli and Staphylococcus aureus. The antioxidant properties of gallic acid embedded in films were measured. Composite films containing 70 wt% KGM (Ca-KG7) displayed the best properties. These findings suggest an alternative method for synthesis of GG-based packaging films with improved properties.