Mannich-modified benzaldehyde chitosan as a capping agent for silver nanocomposites: enhanced antibacterial...

Chitosan, a biocompatible and biodegradable biopolymer, was chemically modified via a one-pot Mannich reaction under reflux to synthesize benzaldehyde-based β-aminocarbonyl chitosan (BACC-B). The obtained BACC-B was a brown solid with a yield of 75.5% (w/w) and a degree of substitution (DS) of 23%. To enhance antibacterial performance, BACC-B was incorporated with silver (Ag) to form BACC-B/Ag composites, where BACC-B acted as a capping agent to inhibit Ag agglomeration. Composites were synthesized using 0, 1, 3, 6, 10, and 15 mol equivalents of ascorbic acid relative to 1 mol equivalent of AgNO₃ precursor, while chitosan/Ag (6 equivalents) was prepared as a comparison. Characterization was conducted using UV-Vis spectrophotometry, FTIR, and AAS for Ag quantification. The 6-equivalent BACC-B/Ag composite exhibited the most balanced performance, with a yield of 45.80% and a surface plasmon resonance (SPR) peak at 433 nm, indicating nanoparticle formation. Chitosan/Ag showed an SPR peak at 424 nm with a higher Ag content (0.73%) compared to BACC-B/Ag (0.57%). All composites formed greenish-brown solids. Antibacterial activity evaluated by the total plate count (TPC) method on chicken meat during 0, 3, and 7 days of storage demonstrated significant bacterial reduction. The BACC-B (2500 ppm) and BACC-B/Ag (2500 ppm) samples showed reductions of 92.30% and 96.33%, respectively, on day 3, indicating strong short-term antibacterial potential for food preservation applications.