Preparation of curcumin-loaded chitosan/polyvinyl alcohol intelligent active films for food packaging and freshness monitoring.

To fulfill the current need for intelligent active food packaging. This study incorporated the curcumin inclusion complexes (CUR-CD) into chitosan/polyvinyl alcohol polymer to develop a new intelligent active film. The structures of films were analyzed by Fourier-transform infrared (FT-IR), scanning electron microscope (SEM), and so on. The CP-Cur150 film displays exceptional mechanical properties, water vapor barrier, and UV blocking capabilities as demonstrated by physical analysis. The CP-Cur150 film exhibited free radical scavenging rates on 2,2-diazo-di-3-ethylbenzothiazolin-6-sulfonic (ABTS) (98 %) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (87 %). Additionally, it showed inhibitory effects on Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli), reducing live colony counts by approximately 2.7 and 1.3 Log10 CFU/mL, respectively. The films were used to monitor the shrimp's freshness in real time. With the spoilage of shrimp, the film exhibited clear color fluctuations, from light yellow to red. In addition, the evaluation of the impact of films on pork pH, total volatile basic nitrogen, and total bacterial counts demonstrated that the CP-Cur150 film displayed the most significant effectiveness in preserving freshness, thereby extending the shelf life of pork.

Gelatin/carboxymethylcellulose composite film combined with photodynamic antibacterial: New prospect for fruit preservation.

Plastic packaging causes environmental pollution, and the development of simple and effective biodegradable active packaging remains a challenge. In this study, gelatin (G) and sodium carboxymethylcellulose (CMC) were used as film materials, with the addition of curcumin (Cur), a photosensitive substance, to investigate the changes in the physical and chemical properties of the film and its application in fruit preservation. The results demonstrated that Cur was compatible with the film. With the addition of Cur, the thickness of the film increased up to 1.3 times, while the moisture content was reduced to 12.10 %. The tensile strength (TS) and elongation at break (EAB) of the film can reach 8.84 MPa and 19.33 %, respectively. The photodynamic antibacterial experiment revealed that the film containing 0.5 % Cur exhibited the highest antibacterial rate, reaching 99.99 % against Staphylococcus aureus (S. aureus) and 95 % against Escherichia coli (E. coli). During storage, the grapes remained unspoiled for up to 9 days after being phototreated with the film and the microbial content of the skin was much lower than that of the control group. In addition, Cur provided antioxidant activity for the film, with a scavenging activity of 39.54 % against the 2,2-diphenyl-1-picrind radical (DPPH). Bananas exposed to the film-forming solution for a short period of time remained fresh for up to 6 days. During preservation, the weight of the treated bananas decreased more slowly than that of the control group. In addition, the activity of SOD on the 7th day was approximately 20 U/g higher than that of the control group, which helped to reduce oxidative stress during banana preservation. In summary, G-CMC/Cur film is an optional fruit-cling film that can be used in food packaging.

Photodynamic antibacterial application of TiO2/curcumin/hydroxypropyl-cyclodextrin and its konjac glucomannan composite films.

Although photodynamic therapy (PDT) has great advantages for the treatment of bacterial infections, photosensitizers (PSs) often have many disadvantages that limit their application. Improving the shortcomings of PSs and developing efficient PDT antimicrobial materials remain serious challenges. In this study, a nanocomposite drug (TiO2/curcumin/hydroxypropyl-cyclodextrin, TiO2/Cur/HPCD) was constructed and combined with konjac glucomannan to form composite films (TiO2/Cur/HPCD films, KTCHD films). The stabilities of TiO2 and Cur were improved in the presence of HPCD. The particle size of TiO2/Cur/HPCD was approximately 33.9 nm, and the addition of TiO2/Cur/HPCD enhanced the mechanical properties of the films. Furthermore, TiO2/Cur/HPCD and KTCHD films exhibited good biocompatibility and PDT antibacterial effects. The antibacterial rate of TiO2/Cur/HPCD was 74.46 % against MRSA at 500 µg/mL and 99.998 % against E. coli at 400 µg/mL, while it was adsorbed on the surface of bacteria to improve the effectiveness of the treatment. In addition, studies in mice confirmed that TiO2/Cur/HPCD and KTCHD films can treat bacterial infections and promote wound healing, with a highest wound healing rate of 84.6 % in the KTCHD-10 films + Light group on day 12. Overall, TiO2/Cur/HPCD is a promising nano-antibacterial agent and KTCHD films have the potential to be employed as antibacterial and environment-friendly trauma dressings.

Methylene Blue/Carbon Dots Composite with Photothermal and Photodynamic Properties: Synthesis, Characterization, and Antibacterial Application.

Photodynamic therapy and photothermal therapy provide new ways to combat antibiotic resistance. In this research, methylene blue (MB) as an effective photosensitizer was conjugated with carbon quantum dots (CQDs), the composite product not only possessed good antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) due to excellent singlet oxygen (1 O2 ) production rate and light heat transfer performance, but also showed good biocompatibility. Combined with 808 nm and 660 nm laser irradiation, the minimum bactericidal concentration of CQDs-MB towards S. aureus and E. coli was 5 µm. Therefore, this study provides a potential candidate material based on CQDs for clinical applications.

Curcumin-loaded multifunctional chitosan gold nanoparticles: An enhanced PDT/PTT dual-modal phototherapeutic and pH-responsive antimicrobial agent.

Overuse of antibiotics has led to the emergence of multidrug resistant (MDR) bacteria.. Photothermal (PTT) and photodynamic therapy (PDT) have may be effective alternatives for antibiotics in the treatment of bacterial infections. In this study, based on chitosan (CS)-coated gold nanoparticles, a pH stimulus-responsive drug delivery system was developed, which can anchor to the cell membrane for photodynamic therapy and photothermal therapy, and enhance the therapeutic potential of curcumin (Cur). Release experiments showed that AuNPs/CS-Cur nanocomposites released curcumin in a pH-dependent manner, which may facilitate the drug to be delivered to the acidic bacterial infection environment. CS as the outer layer covered on gold nanoparticles could improve the dispersibility of Cur in aqueous solution, gold nanoparticles prevent rapid photobleaching of curcumin, thus ensuring the yield of singlet oxygen under irradiation, and enhance the electrostatic binding with bacteria cell membrane. Under light conditions, AuNPs/CS-Cur can produce a large amount of reactive oxygen species and heat to kill S. aureus and E. coli. Compared with free Cur-mediated PDT, the complex significantly improved the synergistic PTT/PDT photoinactivation ability against S. aureus and E. coli. In addition, AuNPs/CS-Cur had good biocompatibility. Therefore, AuNPs/CS-Cur possessed the characteristics of electrostatic targeting, photodynamic and photothermal antibacterial therapy, which would become an efficient and safe antibacterial nano-platform and provide new ideas for the treatment of bacterial infection.

[Respiration from density fractions of two cultivated soils and its temperature sensitivity].

To investigate respiration from density fractions of cultivated soils and its temperature sensitivity, laboratory incubations of upland and paddy soils were carried out for a period of 63 days at four temperature levels of 5, 15, 25 and 35 °C. The upland and paddy soil samples were taken from Pingyi of Shandong Province and Taojiang of Hunan Province, respectively. CO2 efflux from light fraction (LF), heavy fraction (HF) and bulk soil (BS) was measured during the incubation. The results indicated that bulk soil respiration was significantly higher than either light or heavy fraction respiration regardless of soil type. Respiration from HF was higher than that from LF in the upland soil. In the temperature range from 5 to 25 °C, light and heavy fraction respiration in the paddy soil did not show significant difference, while the HF exhibited higher respiration than the LF at 35 °C. Over the 63-day incubation with various temperatures, cumulative respiration from the LF, the HF and the BS accounted for 0.3%-2.8%, 0.4%-3.7% and 0.6%-7.0% of the original LF, HF and BS carbon in the upland soil, and 0.4%-3.0%, 0.3%-3.8% and 0.7%-5.3% of their original carbon in the paddy soil. The temperature sensitivity of the CO2 efflux from the LF, HF and BS, which was expressed as Q10 value, declined as the incubation proceeded. The Q10 values for the HF were generally higher than the values for the LF in the paddy soil, while the difference of Q10 values between the HF and the LF was divergent in the upland soil. In the temperature range from 5 to 25 °C, the Q10 values for BS respiration were higher in the upland soil than in the paddy soil, but it was opposite in the temperature range from 25 to 35 °C. Our results using the site-specific soils suggested that the decomposition of organic carbon in the upland soil was faster and could be more sensitive to temperature change than in the paddy soil.