Photo-induced antifungal activity of chitosan composite film solution with Nano TiO2 and Nano Ag

This study investigated the ultraviolet (UV) light-induced effect of chitosan-titanium dioxide-silver (CTS-TiO2-Ag) nanocomposite film solution against Penicillium steckii ( ( P. steckii ) , as well as the underlying the physiological mechanism. The results indicated that the longer the UV exposure time, the better the pathogenic inhibition effect. After UV photoinduced treatment for 120 min, the colony diameter of P. steckii was the smallest at 4.85 mm. However, when this process is followed by an 8-h storage period, the conductivity of the P. steckii culture medium reached its highest level at 713 μs/cm. After a 120 h growth period in the same conditions, the lesion diameters and pathogenicity of the mangoes reached 12.61 mm and 41.67%, respectively. Since the cell membrane was severely disrupted, its permeability increased, causing serious intracellular protein and nucleic acid material extravasation. Furthermore, the malondialdehyde (MDA) , catalase (CAT) and superoxide dismutase (SOD) in the P. steckii reached maximum levels after 8 h of incubation, at 2.1106 μmol/mL, 44.06 U/mL, and 24.67 U/mL respectively. These results indicated significant P. steckii inhibition via the UV light induction of the CTS-TiO 2 -Ag composite film solution.

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.

Graphene and Chitosan Composite Film Modified Electrode as a Sensitive Voltammetric Sensor for Tyrosine Detection in Food and Biological Samples

A voltammetric sensor made from a graphene and chitosan modified glassy carbon electrode (GR-CTS/GCE) was fabricated for accurate analysis of tyrosine (Tyr) in both food and biological samples. The surface morphology of the electrode and the properties of the electrode-electrolyte interface were determined by scanning electron microscopy and cyclic voltammetry. Compared with a bare GCE, the synergistic effect of GR and CTS is obvious. The peak current increases 35.6 times. The experimental conditions were optimized by second derivative linear sweep voltammetry (SDLSV) and Tyr was quantitatively analyzed on the electrode. The study shows that the oxidation peak current of Tyr obtained in 0.1 M pH 2.7 phosphate buffer is proportional to its concentration between 0.006-0.8 and 0.8-10.0 μM, with the low detection limit being 4.0 nM (signal/noise = 3). Excellent anti-interference ability was demonstrated by investigating the voltammetric response of Tyr in mixtures containing other biomolecules. In addition, the sensor exhibited good stability and repeatability. Through the detection of Tyr in milk and serum samples, the effectiveness of the sensor was studied, and the results were satisfactory.