Preparation and preservation properties of the chitosan coatings modified with the in situ synthesized nano SiOx

Volatile profile of postharvest hardy kiwifruits treated with chitosan-silica nanocomposite coatings

Chitosan (CTS) is a natural polysaccharide derived from the deacetylation of chitin. Chitosan-based coatings are widely used for the preservation of hardy kiwifruits. However, the effect of chitosan-based coating on fruit flavor during ripening is rarely reported. In this study, the postharvest qualities of hardy kiwifruits were investigated using chitosan coating and chitosan-silica nanoparticle coating (CTS-SiNPs) during storage at 25°C and 4°C. Physicochemical analyses showed that chitosan coating extended the shelf-life by delaying ripening and maintaining higher quality than uncoated fruits, and CTS-SiNPs treatment showed a superior preservation effect compared to CTS treatment. Untargeted metabolomics analysis based on HS-SPME-GC-MS was used to comprehensively evaluate the volatile profiles of hardy kiwifruits during postharvest storage. The metabolomics analysis showed that two chitosan coating treatments greatly delayed the accumulation of most volatiles while delaying the ripening process, and the differential volatiles were mostly involved in the terpenoids biosynthesis pathway. Notably, most green leaf volatiles (C6/C9 aldehydes, esters and alcohols) and methyl salicylate were up-regulated in the CTS-SiNPs coating groups. In addition, odor activity value (OAV) was used to characterize the key aroma-active compounds and odor profiles. A total of 32 compounds were identified as key aroma-active compounds (OAV ≥ 1) in hardy kiwifruits. The odor profile evaluation showed that the CTS-SiNPs coating treatment enhanced the intensity of the "herbal" odor, while reducing the intensity of "sweet" and "floral" odors in hardy kiwifruits at the eating-ripe stage.

Effect of solvent acids on the microstructure and corrosion resistance of chitosan films on MAO-treated AZ31B magnesium alloy

This study evaluated the effect of solvent acids on the structure and corrosion resistance performance of chitosan (CS) film on MAO-treated AZ31B magnesium (Mg) alloy. Initially, CS solutions were prepared in four solvent acids: acetic acid (HAc), lactic acid (LA), hydrochloric acid (HCl), and citric acid (CA). The CS films were subsequently deposited on MAO-treated AZ31B Mg alloy via a dip-coating technique. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR), contact angle measurement, and atomic force microscopy (AFM) were employed to characterize the surface and cross-sectional morphology as well as chemical composition. Furthermore, the samples were subjected to potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests to assess their resistance against corrosion in simulated body fluid (SBF). These results indicated that the CS film prepared with LA exhibited the lowest surface roughness (Ra = 31.2 nm), the largest contact angle (CA = 98.50°), and the thickest coating (36 μm). Additionally, it demonstrated superior corrosion protection performance, with the lowest corrosion current density (Icorr = 3.343 × 10-7 A/cm2), highest corrosion potential (Ecorr = -1.49 V), and highest polarization resistance (Rp = 5.914 × 104 Ω·cm2) in SBF. These results indicated that solvent acid types significantly influenced their interactions with CS. Thus, the structure and corrosion protection performance of CS films can be optimized by selecting an appropriate solvent acid.

Novel Halogenated Curcumin-Mediated Photodynamic Inactivation for the Preservation of Small Yellow Croaker (Larimichthys polyactis)

A novel class of halogenated curcumin, X-Cur (X = F, Cl, or Br), was synthesized, and its photosensitivity was evaluated. The results showed that Br-Cur with the highest singlet oxygen (1O2) generation capacity exhibited a better photodynamic inactivation (PDI) effect on the small yellow croaker (Larimichthys polyactis) than curcumin. This was attributed to the heavy atom effect of Br, which resulted in Br-Cur having the smallest singlet-triplet energy difference ΔEst(S1-T3) (0.140 eV) and the largest spin-orbit coupling value (0.642262 cm-1). When L. polyactis was treated with 0.025 wt % Br-Cur and exposed to blue LED irradiation (450 nm, 20 mW/cm2) for 20 min, the increase in the total volatile basic nitrogen content (28.23 ± 2.38 mg/100 g on day 6), pH, and total viable count (6.13 ± 0.06 log CFU/g on day 6) could be effectively controlled. Accordingly, Br-Cur is a promising photosensitizer for PDI preservation.

Curcumin-loaded food-grade nano-silica hybrid material exhibiting improved photodynamic effect and its application for the preservation of small yellow croaker (Larimichthys polyactis)

Two types of curcumin-loaded food-grade nano-silica (F-SiO2) hybrid materials were successfully synthesized using the rotary evaporation method (F-SiO2@Cur) and the adsorption method (Cur@F-SiO2). The microstructure and spectral analyses confirmed that the curcumin in F-SiO2@Cur was loaded within the nanopores in a non-aggregate form rather than being adsorbed onto the surface (Cur@F-SiO2). Additionally, F-SiO2@Cur exhibited remarkable water solubility (1510 ± 50.33 µg/mL) and photostability (a photodegradation ratio of only 59.22 %). Importantly, F-SiO2@Cur obtained a higher capacity for the generation of singlet oxygen (1O2) compared to control groups. Consequently, F-SiO2@Cur-mediated photodynamic inactivation (PDI) group attained the highest score in sensory evaluation and the best color protection effect in PDI experiment of small yellow croaker (Larimichthys polyactis) at 4 °C. Moreover, F-SiO2@Cur could effectively controlled total volatile basic nitrogen (TVB-N) content, pH, and total viable count (TVC), thereby prolonging the shelf life. Therefore, F-SiO2@Cur-mediated PDI is an effective fresh-keeping technology for aquatic products.

Eco-friendly flaxseed mucilage biofilms fabricated by gamma irradiation

With looming the global energy crisis and environmental problems Biodegradable green blends based on natural resources and biodegradable polymers have increasingly attracted many researches interest due to their advantages of low cost, use of renewable resource, and biodegradability. In this study, flaxseed mucilage (FM) was extracted with distilled water and utilised to make films with varying ratios of polyvinyl alcohol (PVA) and chitosan (Cs). Gamma irradiation was used as green method to improve the performance of the produced films. Then the films were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectrophotometry and XRD analysis. The tensile measurements, moisture content were used to evaluate the films’ qualities. When flaxseed mucilage is mixed with PVA/Cs blend, it forms films that are less resistive, less rigid, and more flexible, improves mechanical properties and thermal stability. Films containing mucilage and PVA/Cs blend exhibited a compact and homogeneous structure under SEM, confirming the FTIR spectra that suggested a chemical interaction between these three biopolymers. Based on all above properties of the developed films, it can be envisaged to use these films for packaging applications.

Effects of chitosan and nano-SiO2 concentrations on the quality of postharvest guavas (Psidium guajava L.)

Guava (Psidium guajava L.) is a perishable fruit susceptible to postharvest losses at tropical ambient temperature. Therefore, the development of green storage solution such as biodegradable film could be an alternative to increase guavas’ shelf life. The primary objective of the present work was to explore the effects of combining chitosan and nano-SiO2 coating at different concentrations on the external and internal quality parameters of guavas during 12-d storage at 15°C, and 8-d storage at 30°C. Weight loss, skin colour, firmness, ascorbic acid content, total soluble solids (TSS), decay incidence, and sensory taste score during storage were also analysed. Guavas coated with 2% chitosan and 0.02% nano-SiO2 film were economically optimum to maintain the tested postharvest quality parameters, including better skin colour, higher TSS, fruit firmness, ascorbic acid content, and good taste scores, while keeping lower weight loss and decay incidence when compared with those of other treatments at both tested temperatures. Therefore, chitosan and nano-SiO2 as a coating is a promising strategy for improving the postharvest quality of guavas.

Characterization and release kinetics model of thymol from starch-based nanocomposite film into food simulator

To improve the performance of potato starch films and solve the problems of high volatility and low stability of thymol (Thy), thymol was loaded into the channel of SBA-15 to prepare Thy-SBA-15, and the Thy-SBA-15/potato starch film was prepared. The results showed thymol was successfully loaded into the pores of SBA-15. The addition of Thy-SBA-15 enhanced the tensile strength of potato starch film (3.93 Mpa), reduced the water vapor permeability (1.56 × 10^-12  g·d^-1  m^-1  Pa^-1 , WVP) and moisture absorption (80.97%, MA), which enhanced the barrier properties of the films. Thy-SBA-15 had good compatibility with potato starch films. Notably, the thymol released from Thy-SBA-15/potato starch film was initially explosive, and then continuous, which showed this film could effectively slow down the release rate of thymol and prolong the fresh-keeping period of food. The Korsmeyer-Peppas model M t M ∞ = k t n $$ \left(\frac{{\mathrm{M}}_{\mathrm{t}}}{{\mathrm{M}}_{\infty }}=\mathrm{k}{\mathrm{t}}^{\mathrm{n}}\right) $$ (R²  > .96) had the best fit for the release curve of thymol. PRACTICAL APPLICATIONS: This work offers a new method for the preparation of potato starch sustained-release antibacterial film, and provides a theoretical basis and technical support for the development of intelligent packaging.

Preparation of three-layer flaxseed gum/chitosan/flaxseed gum composite coatings with sustained-release properties and their excellent protective effect on myofibril protein of rainbow trout

Plant essential oils lose their activity due to unstable chemical properties and volatility, and the coating can improve their stability by encapsulating. The three-layer coatings were prepared by tape casting method with flaxseed gum (FG) and chitosan (CS) as film-forming materials, eugenol (EG) and laurel essential oil (LEO) as preservatives. The composite coatings were characterized, and their physicochemical properties, release properties, antibacterial and antioxidant properties were determined. Meanwhile, the protective effect of the composite coatings on rainbow trout fillets myofibril protein was studied. The mechanical properties of the FG/CS/FG coatings are better than FG coating. The release of EG and LEO from the coatings are followed simple diffusion mechanism. After added essential oils, the antibacterial and antioxidant properties of the composite coatings are significantly enhanced. In the preservation process of the rainbow trout fillets, the composite coatings can reduce the carbonyl content, increase the sulfhydryl content and Ca²⁺-ATPase activity. The β-sheet content is 6.09%-15.63% higher than that of control, indicating the coatings are helpful to maintain the order of myofibril protein. The composite coatings slowed down the decrease of antioxidant enzyme activity, thus delay the protein oxidation. Because of long-term antibacterial and antioxidant properties, the composite coatings have potential value in food preservation or food packaging materials.

Preparation of WPU-based super-amphiphobic coatings functionalized by in situ modified SiOx particles and their anti-biofilm mechanism

Fabrication of anti-wetting coatings with anti-biofouling and anti-biofilm properties has become a hot spot of attention in recent years. However, the anti-biofilm mechanism of anti-bacterial adhesion coatings with different wet resistance properties has not been explored in detail. In this work, SiO_x micro-nano particles were prepared by the Stöber method and were in situ modified. The SiO_x/waterborne polyurethane (WPU) coatings were prepared by the drop coating method, and the coatings with different hydrophobic and oleophobic properties were constructed by modifying the process conditions using SiO_x micro-nano particles as the roughness construction factor. Taking the dominant spoilage bacteria of aquatic products, Shewanella putrefaciens as the object, the anti-bacterial adhesion properties and anti-biofilm mechanism of the SiO_x/WPU coatings were investigated. The results show that, with the unmodified SiO_x particles increasing from 1.2% (w/V) to 4.0% (w/V), the hydrophobicity and thermal stability of the SiO_x/WPU coatings are significantly enhanced, but the oil repellency becomes worse due to the mesoporous structure. After SiO_x micro-nano particles are modified with 1H,1H,2H,2H-perfluorooctyl trichlorosilane (PFOTS), the surface energy of the SiO_x/WPU coatings is decreased, the liquid repellency is improved, and the surfaces are rough with the appearance of fluorocarbon compounds, but the thermal stabilities are slightly reduced. Among them, after the secondary modification of SiO_x micro-nano particles, the SiO_x/WPU coatings showed excellent oil repellency, lower surface energies and higher fluorocarbon content on the surface. Particularly, SiO_x/WPU coatings exhibited super-amphiphobicity after adjusting the amount of concentrated ammonia added during the secondary modification process. Meanwhile, we found that for the hydrophobic SiO_x/WPU coatings, the stronger the oleophobic property, the greater the anti-bacterial adhesion ability is, while the anti-bacterial adhesion ability of hydrophobic and selectively oleophobic or superhydrophobic and oleophobic SiO_x/WPU coatings is poor than that of amphiphilic SiO_x/WPU coatings. However, because the super-amphiphobic SiO_x/WPU coatings can be in the Cassie state with the bacterial solution for a long time, it can "capture" enough air to inhibit the irreversible adhesion of the bacteria. More importantly, the coatings can also inhibit the metabolic activity, secretion of extracellular polysaccharides, and activities of ATPase and AKP of the adherent bacteria, so it has a better anti-biofilm property. The anti-biofilm coatings can be used as food packaging materials or coated on the inner surface of packaging boxes to prevent the microbial infection.

In vitro biological and antimicrobial properties of chitosan-based bioceramic coatings on zirconium

Ca-based porous and rough bioceramic surfaces were coated onto zirconium by micro-arc oxidation (MAO). Subsequently, the MAO-coated zirconium surfaces were covered with an antimicrobial chitosan layer via the dip coating method to develop an antimicrobial, bioactive, and biocompatible composite biopolymer and bioceramic layer for implant applications. Cubic ZrO₂, metastable Ca_0.15Zr_0.85O_1.85, and Ca₃(PO₄)₂ were detected on the MAO surface by powder-XRD. The existence of chitosan on the MAO-coated Zr surfaces was verified by FTIR. The micropores and thermal cracks on the bioceramic MAO surface were sealed using a chitosan coating, where the MAO surface was porous and rough. All elements such as Zr, O, Ca, P, and C were homogenously distributed across both surfaces. Moreover, both surfaces indicated hydrophobic properties. However, the contact angle of the MAO surface was lower than that of the chitosan-based MAO surface. In vitro bioactivity on both surfaces was investigated via XRD, SEM, and EDX analyses post-immersion in simulated body fluid (SBF) for 14 days. In vitro bioactivity was significantly enhanced on the chitosan-based MAO surface with respect to the MAO surface. In vitro microbial adhesions on the chitosan-based MAO surfaces were lower than the MAO surfaces for Staphylococcus aureus and Escherichia coli.

Characterization and release kinetics study of potato starch nanocomposite films containing mesoporous nano-silica incorporated with Thyme essential oil

This study aimed to develop potato starch nanocomposite films containing mesoporous nano-silica (SBA-15, SBA-16 and MCM-41) incorporated with Thyme essential oil (TEO). TEO-SBA-15/potato starch films, TEO-SBA-16/potato starch films and TEO-MCM-41/potato starch films were prepared based on potato starch. The physical and mechanical properties of the nanocomposite films were also investigated. The results showed that the addition of mesoporous nano-silica incorporated with TEO improved the properties of potato starch nanocomposite films. Especially, the addition of TEO-MCM-41 markedly enhanced the tensile strength (4.33 MPa), and reduced the water vapor permeability (1.80 g·m^-1·h^-1·KPa^-1) and moisture absorption (37.67%) of potato starch nanocomposite films. The results of scanning electron microscopy (SEM) analysis showed that TEO-MCM-41 hardly agglomerated in the potato starch nanocomposite films. Additionally, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) confirmed that strong hydrogen bonds were formed between TEO-MCM-41 and potato starch. The release kinetics of TEO proved that incorporating TEO into the pores of mesoporous nano-silica could delay its release rate, and the Peleg model (t/(M_t - M₀) = K₁ + K₂t) was suitable for describing the release behavior. The findings of this study suggested that TEO-MCM-41/potato starch films had a good application prospect in the field of slow-releasing and antimicrobial packaging materials.

Advances in the application of chitosan as a sustainable bioactive material in food preservation

Chitosan is obtained from chitin and considered to be one of the most abundant natural polysaccharides. Due to its functional activity, chitosan has received intense and growing interest in terms of applications for food preservation over the last half-century. Compared with earlier studies, recent research has increasingly focused on the exploration of preservation mechanism as well as the targeted inhibition with higher efficiency, which is fueled by availability of more active composite ingredients and integration of more technologies, and gradually perceived as "chitosan-based biofilm preservation." In this Review, we comprehensively summarize the potential antimicrobial mechanisms or hypotheses of chitosan and its widely compounded ingredients, as well as their impacts on endogenous enzymes, oxidation and/or gas barriers. The strategies used for enhancing active function of the film-forming system and subsequent film fabrication processes including direct coating, bioactive packaging film and layer-by-layer assembly are introduced. Finally, future development of chitosan-based bioactive film is also proposed to broaden its application boundaries. Generally, our goal is that this Review is easily accessible and instructive for whose new to the field, as well as hope to advance to the filed forward.

Preparation, characterization and antibacterial mechanism of the chitosan coatings modified by Ag/ZnO microspheres

BACKGROUND

To improve the physicochemical and antibacterial properties of coatings, the chitosan (CS) coatings were respectively prepared by a casting method with zinc oxide (ZnO) and silver (Ag)/ZnO microspheres as modifiers. The chemical structures and micromorphology of ZnO, Ag/ZnO microspheres and CS coatings were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. Furthermore, using the dominant spoilage bacteria of aquatic products, Shewanella putrefaciens and Pseudomonas aeruginosa, as objects, the antibacterial activities and mechanism of the CS coatings were investigated.

RESULTS

The results show that ZnO and Ag/ZnO microspheres are dispersed homogeneously in the CS coatings. After modified by ZnO and Ag/ZnO microspheres, the mechanical properties and antibacterial abilities of the CS coatings are improved, and that of 0.5% Ag/ZnO-CS coating is the optimal. For pure CS coating, the bacterial cell membrane is damaged slightly because of the electrostatic interaction between NH³⁺ of CS and the negative charge on bacterial surface. After treated by ZnO-CS composite coating, the bacterial cell membrane is destroyed badly on account of the earlier-mentioned ion interaction and disturbing the synthesis of high molecular weight total protein.

CONCLUSION

With regard to Ag/ZnO-CS composite coating, the bacterial cell membrane is damaged seriously and cell contents are completely released due to ion interaction, disturbing the synthesis of high molecular weight total protein and low molecular weight membrane protein. Hence, Ag/ZnO-CS composite coatings are antimicrobial materials and food preservative materials with great potential application. © 2020 Society of Chemical Industry.

Preparation, physicochemical and preservation properties of Ti/ZnO/in situ SiOx chitosan composite coatings

BACKGROUND

Among nanomaterials, Ti and ZnO nanoparticles are often chosen as preservation materials because of their antibacterial properties. Chitosan, as a natural biopolymer, has potential because of its abundance, compatibility and antibacterial properties. To improve the physicochemical and preservation properties of in situ SiOx chitosan (CS) composite coating, Ti/ZnO/SiOx CS composite coatings were prepared with Ti-doped ZnO (Ti/ZnO) nanorods and nanoballs. The composite coating structures were characterized by Fourier transform infrared, X-ray diffraction and scanning electron microscopy, and their physicochemical and preservation properties were determined simultaneously.

RESULTS

The results show that the Ti/ZnO nanoparticles are beneficial to homogeneous dispersion of in situ synthesized nano SiOx in the CS coating, and that Ti/ZnO nanoballs have better dispersion than Ti/ZnO nanorods. Moreover, strong hydrogen bonds are formed among Ti/ZnO nanoparticles and in situ synthesized nano SiOx and CS molecules, and the primary structure of CS is disorganized. Thereby, the gas permeabilities and mechanical properties of the CS coatings are improved due to modification of Ti/ZnO nanoparticles, and the Ti/ZnO nanoballs/SiOx CS composite coating is optimal. The preservation properties of the CS coatings on Sciaenops ocellatus are significantly improved, and those of Ti/ZnO/in situ SiOx CS composite coatings are superior.

CONCLUSION

The preservation properties of the CS composite coatings on S. ocellatus are significant, and the Ti/ZnO nanoballs/SiOx CS composite coating is even better. Therefore, the co-modification method of in situ nanoparticles and antibacterial nanoparticles may be a promising method to improve the preservation properties of CS coatings. © 2019 Society of Chemical Industry.

Effect of Nano-SiOx/Chitosan Complex Coating on the Physicochemical Characteristics and Preservation Performance of Green Tomato

A novel nano-silicon oxides (SiOx)/chitosan complex film was prepared using ultrasonic assistant in the process of dissolving chitosan and silicon oxides (SiOx), and characterized by transmission electron microscopy. Its effect on quality preservation of tomatoes (Solanum lycopersicum L. cv. Zheza 205) was investigated under ambient temperature. The results revealed that the nano-SiOx/chitosan complex (NSCC) film retarded weight loss and softness, delayed the titratable acids and total soluble solids loss, and thus markedly extended shelf life of green tomatoes. The antimicrobial activity of tomatoes coated with NSCC film was also recorded higher compared to chitosan (Ch) films and control. In addition, the NSCC film-coated tomatoes prevent the increase of malondialdehyde content and total polyphenol content. Moreover, the peroxidase activity, phenylalanine ammonia-lyase activity, and polyphenoloxidase activity of tomatoes coated with NSCC film were found lower than that in other treatments. These data indicated that the beneficial effects of nano-SiOx/chitosan complex coating on postharvest quality were possibly associated with the lower rate of O₂/CO₂ transmission coefficient, limiting food-borne pathogenic bacterial growth, higher antioxidant activities, and also higher reactive oxygen species (ROS) scavenging and anti-browning activities of related enzymes in the tomatoes. Further, the results of the study could be used to successfully develop a novel nano-SiOx/chitosan complex film for improving the postharvested quality of tomatoes and thus effectively utilized by the food packaging industry.

Synergistic effect of a novel chitosan/silica nanocomposites-based formulation against gray mold of table grapes and its possible mode of action

Ecofriendly nanostructured materials have been proposed as promising alternative control means to prevent plant diseases. Chitosan nanoparticles (CN), silica nanoparticles (SN) and chitosan-silica nanocomposites (CSN) were synthesized and their morphology and structure was characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM), infrared spectra (FT-IR) and Raman spectroscopy. Their antifungal efficiency against Botrytis cinerea, the causal fungus of gray mold disease of table grapes, was tested in vitro and in vivo (under artificial and natural infections). In vitro tests showed that CN, SN and CSN reduced fungal growth by 72, 76 and 100%, respectively at 1% as compared to control. Under natural infection, at the end of cold storage, CSN was the most effective treatment, and reduced the development of gray mold by 59 and 83%, for 'Italia' and 'Benitaka' grapes, respectively as compared to the water control. Results indicate that a synergistic effect of CSN against gray mold was observed. The impact of tested nanocomposites on soluble solids - TSS, titratable acidity - TA, TSS/TA, berry color, mass loss, stem browning and shattered berries was investigated. No negative effect of tested nanomaterials in term of grape quality was observed. For 'Italia' table grape, CN and CSN can preserve bunches from mass loss as compared to control. Also, the effect of CSN on reactive species of oxygen (ROS), ATP content and mitochondrial membrane potential (MMP) of B. cinerea spores was determined to verify its mode of action. The obtained results suggested CSN, as alternative control means, to reduce/substitute the use of fungicides to control gray mold of table grapes while maintaining grape quality.

Characterization and application of the microencapsulated carvacrol/sodium alginate films as food packaging materials

The carvacrol (CAR) was microencapsulated by β-cyclodextrin (βCD). To extend the shelf-life of white mushrooms against Trichoderma sp., the microencapsulated CAR (βCD-CARM)/sodium alginate (SA) films were prepared and characterized. The antifungal, physical, and mechanical properties of the films were investigated in this study. The results showed that the βCD-CARM with a core-to-wall ratio of 1:10 had better encapsulation efficiency and antifungal activity against Trichoderma sp., which was isolated from postharvest white mushrooms stored at 4 °C. The optimum concentration of βCD-CARM against Trichoderma sp. in vitro was 15 g/L. The water resistance, mechanical properties, light barrier property and heat aging of the film were enhanced after adding βCD-CARM. The films with 30 g/L βCD-CARM could efficiently against Trichoderma sp. The performance of βCD-CARM/SA films was confirmed to control the release of CAR for enhanced antifungal activity. Besides, the βCD-CARM/SA films increased the activities of active free-radical scavenging enzymes to alleviate oxidative damage and delay senescence of the postharvest white mushrooms.

Antimicrobial Nanoparticles Incorporated in Edible Coatings and Films for the Preservation of Fruits and Vegetables

Edible coatings and films (ECF) are employed as matrixes for incorporating antimicrobial nanoparticles (NPs), and then they are applied on the fruits and vegetables to prolong shelf life and enhance storage quality. This paper provides a comprehensive review on the preparation, antimicrobial properties and mechanisms, surface and physical qualities of ECF containing antimicrobial NPs, and its efficient application to vegetables and fruits as well. Following an introduction on the properties of the main edible coating materials, the preparation technologies of ECF with NPs are summarized. The antimicrobial activity of ECF with NPs against the tested microorganism was observed by many researchers. This might be mainly due to the electrostatic interaction between the cationic polymer or free metal ions and the charged cell membrane, the photocatalytic reaction of NPs, the detachment of free metal ion, and partly due to the antimicrobial activity of edible materials. Moreover, their physical, mechanical and releasing properties are discussed in detail, which might be influenced by the concentration of NPs. The preservation potential on the quality of fruits and vegetables indicates that various ECF with NPs might be used as the ideal materials for food application. Following the introduction on these characteristics, an attempt is made to predict future trends in this field.

Synthesis and Characterization of Konjac Glucomannan/Carrageenan/Nano-silica Films for the Preservation of Postharvest White Mushrooms

In this study, the konjac glucomannan (KGM)/carrageenan (KC)/nano-silica film was prepared and characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The preservation quality of white mushrooms (Agaricus bisporus) packed using the films was also determined. The nano-silica dosage was found to affect the properties of the nanocomposite KGM/KC films. The results indicated that the properties of the films were significantly improved with the addition of nano-silica. The water vapor permeability, water solubility, moisture absorption, and light transmittance of KGM/KC/nano-silica films were significantly affected by the nano-silica dosage. In this study, the optimal nano-silica dosage to incorporate into the film in order to achieve excellent performance was 0.3%. Strong intermolecular hydrogen bonds were also observed between KGM/KC and nano-silica in the KGM/KC/nano-silica film by FTIR. In addition, the KGM/KC/nano-silica film markedly reduced the browning index, delayed the weight loss and softening, and extended the shelf life of mushrooms during storage at 4 °C. The KGM/KC film modified using nano-silica can provide a potential method for improving the preservation quality of white mushrooms during storage.

The Modification of In Situ SiOx Chitosan Coatings by ZnO/TiO2 NPs and Its Preservation Properties to Silver Carp Fish Balls

The composite chitosan coatings were prepared and characterized to evaluate their preservation properties for silver carp fish balls, and the microstructures and physicochemical properties of the coatings were improved by in situ nano silicon oxide (SiOx) and zinc oxide/titania (ZnO/TiO₂ ) nano-particles (NPs). In the chitosan coatings, when the chitosan combines with NPs by chemical bonds, the crystal lattice is slightly changed due to the modification of NPs. The chitosan coatings modified by NPs showed few cracks, among which sodium hexametaphosphate (SHMP) modified ZnO/TiO₂ /SiOx-chitosan (ZTS-CS) coating is proved to be the optimal one. The change of the freshness index and the texture of the fish balls are delayed by the coatings due to their gas permeability and antibacterial properties. The preservation properties of the chitosan coatings for Silver Carp fish balls are improved by in situ SiOx, and further improved by co-modification of ZnO/TiO₂ NPs. Furthermore, the surface modification of ZnO/TiO₂ NPs enhances the preservation properties of the chitosan coating. PRACTICAL APPLICATION: In our previous study, in situ SiOx was found to improve antibacterial and preservation properties of chitosan coating, leading to extending shelf time of Sciaenops ocellatus. In order to further improve properties of chitosan coatings, we added nontoxic edible nano materials to the in situ SiOx chitosan coatings. In situ SiOx modified by ZnO/TiO₂ NPs were synthesized, measured, and characterized in this study, and were applied for the preservation of silver carp fish balls. It could serve as a potential preservation material due to the increasing mechanical preservation properties. Through the results, the ZnO/TiO₂ /SiOx-chitosan (ZTS-CS) coatings have potential as application in the food industry to guarantee food quality and extend shelf life of products.

Preparation and Characterization of Potato Starch Film with Various Size of Nano-SiO₂

The various sizes (15, 30, 80, and 100 nm) of nano-SiO₂/potato starch films were synthesized and characterized. The gas permeability, antibacterial properties, and mechanical properties of the films were evaluated to their potential for application as food packaging materials. Results indicated that the 100 nm nano-SiO₂ was well dispersed in the starch matrix, which induced an active group on the surface of 100 nm nano-SiO₂ adequately combined with starch macromolecule. The water resistance and mechanical properties of the films were improved with the addition of nano-SiO₂. Notably, resistance to ultraviolet and thermal aging was also enhanced. The nano-SiO₂/potato starch films were more efficient against Escherichia coli (E. coli) than Staphylococcus aureus (S. aureus). Remarkable preservation properties of the films packaging the white mushrooms were obtained, with those of the 100 nm films considered superior. This study can significantly guide the rational choice of the nano-SiO₂ size to meet the packaging requirements of various agricultural products.

Preparation and Antibiofilm Properties of Zinc Oxide/Porous Anodic Alumina Composite Films

The PAA (porous anodic alumina) films were prepared by two-step anodic oxidation after different times, and then the ZnO/PAA composite films were prepared by sol-gel method on their surface. Meanwhile, the ZnO/PAA composite films were characterized by X-ray diffraction (XRD), thermogravimetric/differential thermal analyzer (TG/DTA), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and water contact angle (CA). The antibiofilm properties of ZnO/PAA composite films on Shewanella putrefaciens were measured simultaneously. The results show that the micromorphologies of PAA and ZnO/PAA composite films are affected by second anodization time. ZnO is a hexagonal wurtzite structure, and ZnO particles with a diameter of 10-30 nm attach to the inner or outer surfaces of PAA. After being modified by Si69, the ZnO films translate from hydrophilia to hydrophobicity. The ZnO/PAA film with the optimal antibiofilm properties is prepared on the PAA surface by two-step anodization for 40 min. The adherence of Shewanella putrefaciens is restrained by its super-hydrophobicity, and the growth of biofilm bacteria is inhibited by its abundant ZnO particles.

Effect of zinc oxide film morphologies on the formation of Shewanella putrefaciens biofilm

Zinc oxide (ZnO) films were prepared on aluminum substrate by a hydrothermal method to investigate the effect of their surface characteristics, including morphology and hydrophobicity, on the corresponding antibiofilm performance. The surface characteristics of the prepared ZnO films were examined by a comprehensive range of methodologies, suggesting that films of distinctive surface morphologies were successfully formed. Subsequently, their antibiofilm activities, using Shewanella putrefaciens as a model bacterium, were assessed. Surface measurements confirmed that the ZnO films equipped with a nanoscopic needlelike surface feature are more hydrophobic than those possessing densely packed microflakes. The reduced number of live cells and presence of biofilm, confirmed by optical and electron microscopy results, suggest that the former films possess an excellent antibiofilm performance. It is believed that the engineered nanoscopic needle feature might penetrate the cell membrane when they are in contact, allowing the effective substance of ZnO antibacterial ingredients to diffuse into the embedded bacteria. Furthermore, such surface characteristics might perturb the integrity of the cell membrane causing the intracellular substance is leaked from the cells. As such, the combinatorial effects of nanoscopic feature resulted in an inhibited growth of S. putrefaciens biofilm on ZnO film.

Chitosan-Based Coating with Antimicrobial Agents: Preparation, Property, Mechanism, and Application Effectiveness on Fruits and Vegetables

Chitosan coating is beneficial to maintaining the storage quality and prolonging the shelf life of postharvest fruits and vegetables, which is always used as the carrier film for the antimicrobial agents. This review focuses on the preparation, property, mechanism, and application effectiveness on the fruits and vegetables of chitosan-based coating with antimicrobial agents. Chitosan, derived by deacetylation of chitin, is a modified and natural biopolymer as the coating material. In this article, the safety and biocompatible and antimicrobial properties of chitosan were introduced because these attributes are very important for its application. The methods to prepare the chitosan-based coating with antimicrobial agents, such as essential oils, acid, and nanoparticles, were developed by other researchers. Meanwhile, the application of chitosan-based coating is mainly due to its antimicrobial activity and other functional properties, which were investigated, introduced, and analyzed in this review. Furthermore, the surface and mechanical properties were also investigated by researchers and concluded in this article. Finally, the effects of chitosan-based coating on the storage quality, microbial safety, and shelf life of fruits and vegetables were introduced. Their results indicated that chitosan-based coating with different antimicrobial agents would probably have wide prospect in the preservation of fruits and vegetables in the future.