Tiantian Wu

Structural properties of films and rheology of film-forming solutions of chitosan gallate for food packaging.

The chitosan gallates (CG) were obtained by free-radical-initiated grafting of gallic acid (GA) onto chitosan (CS) in this work. The chemical structures of the CG were corroborated by UV-vis, GPC and (1)H NMR analysis. The grafting reaction was accompanied with a degradation of the CS molecule. The shear-thinning flow behavior of CG film-forming solutions (CG FFS) decreased with the grafting amount of GA into CS chain, while the CG FFS grafted at a lower GA value behaved like a networks containing entangled or cross-linked polymer chains with a more elastic behavior. The increasing of GA grafting onto the CS chain led to a reduction of tensile strength, elongation at break and water resistance in the corresponding films, but increases in the antioxidant and antimicrobial activities were observed. The microstructure of the film was investigated using scanning electron and atomic force microscope, and the results were closely related to the observed film properties.

Integration of lysozyme into chitosan nanoparticles for improving antibacterial activity

Lysozyme was integrated into chitosan nanoparticles (CS-NPs) to improve the antibacterial activity. CS-NPs and chitosan-lysozyme nanoparticles (CS-Lys-NPs) were prepared according to the ionic gelation technique and then characterized by average size, zeta potential, polydispersity index (PDI), atomic force microscopy (AFM), fourier transform infrared (FT-IR), small-angle X-ray scattering (SAXS), circular dichroism (CD) and UV-visible spectroscopy. Antibacterial properties were investigated by transmission electron microscopy (TEM) based on observation of the inhibition zone and measurement of the minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) of CS-NPs and CS-Lys-NPs against E. coli and B. subtilis. The CS-NPs had particle sizes of 476.2-548.1nm, while an increase to ∼488.8 to 613.5nm was observed upon loading with lysozyme. The results suggested that the integration of lysozyme into CS-NPs enhanced the antibacterial activity against E. coli and B. subtilis, which may show great potential for use in the food industry and other applications in the form of direct addition or incorporation into packaging.

Formation of hydrogels based on chitosan/alginate for the delivery of lysozyme and their antibacterial activity

Novel hydrogels based on chitosan/sodium alginate (CS-ALG) were prepared to deliver and protect lysozyme while eliminating food-borne microorganisms. These hydrogels were characterized according to the zeta potential, optical microscopy, scanning electron microscopy (SEM), UV-visible spectroscopy (UV-vis), fourier transform infrared (FT-IR), and small-angle X-ray scattering (SAXS). The results demonstrated that the resultant hydrogels were negatively charged and spherical in shape. In addition, the maximum swelling ratio was 45.66±7.62 for CS-ALG hydrogels loaded with lysozyme. The relative activity of the released lysozyme was 87.72±3.96%, indicating that CS-ALG hydrogels are promising matrices for enzyme loading and adsorption. Furthermore, a 100% bacterial clearance rate of CS/ALG loaded with lysozyme was observed to correspond to the superposition effect stimulated by CS and lysozyme, which improved the antibacterial activity against E. coli and S. aureus compared to CS/ALG, suggesting its potential use in the food industry as well as other applications.

Formation, characterization and release kinetics of chitosan/γ-PGA encapsulated nisin nanoparticles

Nisin is an antibiotic peptide widely used in food and pharmaceutical industry. To improve its efficiency, nisin was encapsulated in a poly-γ-glutamic acid (γ-PGA) and chitosan nanoparticle system using self-assembly method. The effects of the nisin concentration and chitosan coating on the properties of the nanoparticles were investigated. The release behavior and transport mechanism of nisin from the nanoparticles were also examined under different conditions (temperature of 4 and 25 °C and pH of 3.0, 6.0 and 8.0 respectively). Results showed that the loading content (LC) and mean particle size of the nanoparticles were increased with the increasing of nisin concentration, but encapsulation efficiency (EE) was declined. The chitosan coating enhanced the stability of nanoparticle (higher ζ potential) and led to a higher EE and LC, and bigger mean particle size. FT-IR spectroscopy suggested that the formation of nisin/γ-PGA/chitosan nanoparticle (N–P–C-NPs) was mainly attributed to the interactions among the function groups of chitosan, γ-PGA and nisin by hydrogen bonding and electrostatic interactions. The release of nisin from the nanoparticles exhibited a pH-dependent pattern, and the experimental data were fitted to a linear superimposition model which suggested that the release mechanism of nisin from the nanoparticles was an anomalous behavior. In addition, the in vitro antibacterial test showed that N–P–C-NPs was more efficient than nisin/γ-PGA nanoparticle or nisin in inhibiting the growth of Escherichia coli O157:H7 and Listeria monocytogenes, suggesting N–P–C-NPs could be developed as a promising novel food preservative.

Kinetics and mechanism of degradation of chitosan by combining sonolysis with H2O2/ascorbic acid

This study demonstrated the combined use of sonolysis with the H2O2/ascorbic acid (Vc) redox reaction to degrade chitosan (CS). The influence of operating parameters, such as the initial CS concentration (1–15 mg mL−1), the input power level (15–45% of the total input power), the H2O2 and Vc concentration (10–70 mM) and the pH (3.0–5.0) of the reaction solution, on the molecular weight and degradation kinetics of CS were investigated and optimized. Based on the degradation kinetics, a synergetic effect of sonolysis with H2O2 and Vc on the degradation of CS was observed. Structural analysis by FT-IR and 1H and 13C NMR indicated no significant difference between the chemical structure of chitosan before and after degradation. Moreover, intermolecular hydrogen bonds were broken, and the crystallinity of degraded chitosan decreased. Using the above analysis, CS degradation by the combination of sonolysis with the H2O2/Vc redox reaction was proposed to be due to mechanical effects along with HO˙ attack on the β-1,4-glucoside linkages of glucosamine units. These results suggest that the sonolysis/H2O2/Vc combined technique is promisingly suitable for large-scale manufacture of chitooligosaccharide.

Eugenol-chitosan nanoemulsions by ultrasound-mediated emulsification: Formulation, characterization and antimicrobial activity

Eugenol is widely used in food industries where it encounters major concerns such as its poor solubility and stability. Herein, a novel eugenol-nanoemulsion was prepared by using ultrasonication as emulsification techniques, chitosan nanoparticle as carrier, and surfactant, as emulsifier. The results indicated that droplet size and encapsulation efficiency of the nanoemulsions was significantly affected by testing factors. The selected parameters for nanoemulsions were determined as chitosan-eugenol ratio of 1:1, Tween20 1 wt/v%, ultrasonic power 450 W and ultrasonic time 6 min. The nanoparticles were performed in regularly spherical shape distributed within 80-100 nm. Besides, the nanoemulsions showed great storage stability and thermal stability and the nanoeparticles performed excellent antioxidant capacity, antimicrobial activity as well as an initial burst of eugenol followed by plateau. Therefore, eugenol-chitosan nanoemulsions had great potential in food formulations for extending the shelf life.

What is new in lysozyme research and its application in food industry? A review

Lysozyme, an important bacteriostatic protein, is widely distributed in nature. It is generally believed that the high efficiency of lysozyme in inhibiting gram-positive bacteria is caused by its ability to cleave the β-(1,4)-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine. In recent years, there has been growing interest in modifying lysozyme via physical or chemical interactions in order to improve its sensitivity against gram-negative bacterial strains. This review addresses some significant techniques, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), infrared (IR) spectra, fluorescence spectroscopy, nuclear magnetic resonance (NMR), UV-vis spectroscopy, circular dichroism (CD) spectra and differential scanning calorimetry (DSC), which can be used to characterize lysozymes and methods that modify lysozymes with carbohydrates to enhance their various physicochemical characteristics. The applications of biomaterials based on lysozymes in different food matrices are also discussed.

Quality enhancement of large yellow croaker treated with edible coatings based on chitosan and lysozyme

The aim of this study was to evaluate the preservation effect of chitosan (CS) and lysozyme (Lys) coating on the quality of large yellow croaker (Larimichthys crocea) via physicochemical analyses, microbiological and sensorial assessments during refrigerated storage. Results showed that CS films incorporated with 0.6 mg·mL-1 of lysozyme exhibited the strongest inhibition effect against S. aureus, whose inhibition zone was 16.10 ± 0.71 mm. The utilization of CS singly, or CS-lysozyme (Lys) coating significantly reduced lipid oxidation (thiobarbituric acid value, TBA) and improved the sensorial scores of fishes. Control and treated groups exceeded the maximum permissible level (30 mg N/100 g) of total volatile basic nitrogen (TVB-N) in fishery products on days 6 (control) and 9 (CS or CS-Lys treated), respectively. Fish samples reached the value of 7.0 Log CFU/g (Total Viable Count, TVC) on days 15 (control), whereas both CS and CS-Lys treated flesh samples never exceed this limit value during the refrigerated storage. Results of our study indicate CS-Lys have high efficiency in inhibiting microorganism growth and lipid oxidation and in maintaining sensorial quality, which is a promising method to maintain the quality and extend the shelf life of refrigerated fishes.