Development of a pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red for food packaging applications.

In this study, we successfully developed a screen-printed pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red (LCPR) as a colorant for screen printing ink. The LCPR was synthesized via a Mannich reaction, and its successful grafting was confirmed through FT-IR, UV-vis, and NMR spectroscopy. The LCPR exhibited lower crystallinity and thermal stability compared to low molecular weight chitosan (LC) and demonstrated zwitterionic behavior. To create intelligent labels, the LCPR-based ink was efficiently printed on cotton substrates with high resolution. The label exhibited remarkable sensitivity to buffer pH solutions and ammonia gas, leading to distinctive color changes from orange to red to purple. Additionally, the label showed excellent reversibility, storage stability, and leaching resistance to different food simulant solutions. The label was utilized to monitor shrimp freshness, successfully detecting a noticeable color shift upon spoilage. These findings highlight the significant potential of the LCPR-based label as an intelligent food packaging solution, offering pH-responsiveness and color stability for qualitative freshness detection of protein-rich food.

New Chitosan-Grafted Thymol Coated on Gold Nanoparticles for Control of Cariogenic Bacteria in the Oral Cavity.

Chitosan-grafted thymol (CST) coated on gold nanoparticles has been synthesized and characterized for the design of antimicrobial materials. CST was synthesized via adapting the Mannich reaction, and it acted as the capping agent for the synthesis of gold nanoparticles (AuNPs). The grafting of thymol onto the side chain of chitosan has provided a degree of substitution value (%DSNMR) of 10.0%, calculated by nuclear magnetic resonance spectroscopy. UV-visible spectrometry and elemental analysis were used to confirm the successful synthesis of CST through adapting the Mannich reaction. The appropriate concentration of CST for AuNP synthesis was found to be 0.020%w/v. A red-wine colloidal AuNP solution of 2.41-3.30 nM particle size exhibits a strong surface plasmon resonance at 502 nm, which shows negative charges at pH = 9 of -36.37 mV. This result evidenced that the AuNPs showed electrostatic repulsion and CST played a role as a capping agent to provide a good dispersion and stability state. CST coated on the AuNP surface was successfully utilized for the control of cariogenic bacteria in the oral cavity. The results obtained from this study show that the tuning of the capping agent used in the synthesis step strongly influences the latter antimicrobial activity of the nanoparticles against Streptococcus mutans ATCC 25175 and Streptococcus sobrinus ATCC 33402 activity, with an inhibition zone of 15.90 and 14.25 mm, respectively. The average minimum inhibitory concentration values against S. mutans ATCC 25175 and S. sobrinus ATCC 33402 were found to be 25 and 100 mg/L, respectively, whereas the minimum bactericidal concentration values were 100 and 200 mg/L, respectively.

Synthesis of chitosan-based polymeric dyes as colorimetric pH-sensing materials: Potential for food and biomedical applications.

pH-sensitive polymeric dyes were fabricated by grafting phenol red (PR) and rosolic acid (RA) onto chitosan (CS) by a facile method. Successful grafting was confirmed by 1H NMR, FT-IR, UV-vis, XRD, and elemental analysis. The polymeric dyes exhibited no cell toxicity. The colorimetric pH-sensing films were fabricated by blending the polymeric dyes with CS to establish their pH-dependent color properties. The film color changed in the pH range 4-10, which may indicate food spoilage or wound status. Covalently grafting of polymeric dyes in the films led to excellent color stability, leaching resistance, and reversibility. Hence, the synthesized polymeric dyes had potential as pH-indicative colorants for food and biomedical fields.

Silver loaded hydroxyethylacryl chitosan/sodium alginate hydrogel films for controlled drug release wound dressings.

Wound dressings composed of hydroxyethylacryl chitosan (HC) and sodium alginate (SA) were developed with antibacterial activity by loading Ag particles. The formation of Ag particle in the HC/SA films was achieved by an immersion method through in situ chemical reduction of AgNO3 solution and confirmed by FTIR, SEM-EDS, XRD and XRF techniques. The effect of Ag loading in the Ca-crosslinked HC/SA films with different crosslinking density was studied on swelling behavior, mechanical properties, cytotoxicity, antibacterial activity and drug release behavior. The results showed that Ag loading increased swelling degree in phosphate buffer and enhanced mechanical properties. The HC/SA films with Ag loading exhibited antibacterial activity against E. coli and S. aureus as well as no toxicity on Vero cell. In vitro drug release profiles of the films were examined using para-acetylaminophenol, as a soluble model drug. The increase in crosslinking density and Ag loading prolonged drug releasing rate and almost the films showed linearity profiles. It can be concluded that the HC/SA films with Ag loading have a promising potential in modern wound dressings with antibacterial property and controlled drug release.

Dual pH/thermal-dependent coloring polymeric dye through Mannich reaction of chitosan: Synthesis and characterization.

A novel polymeric dye was synthesized by one-pot Mannich reaction of chitosan (CS) and phenolphthalein (PHP). The grafting onto side chain of CS derivatives was confirmed by UV-vis, FT-IR, 1H NMR techniques. The degree of substitution (DS) calculated by 1H NMR and elemental analysis was revealed to increase with increasing mole ratio of formaldehyde and PHP. XRD analysis showed that the grafting through Mannich reaction was caused to amorphous structure in the derivatives. Covalent grafting of PHP onto CS made the grafted products showing pink color in basic conditions without leaching of dye and color fading after several weeks. Moreover, the derivatives dissolved in LiOH/urea systems could showed darker pink after heating. The results suggested that the novel CS derivatives with dual pH/thermal-dependent coloring property could potentially be prepared as pH/thermal-responsive biomaterial in a wide range of applications.