Synthesis and antibacterial activity of quaternized β-glucans from Poria cocos

This study employed linear unbranched β-1,3-D-glucan from Poria cocos (PCPA) as the raw material and synthesized a series of quaternized polysaccharides (QPCPA) with tunable degrees of substitution via a stepwise pH-controlled nucleophilic substitution method using glycidyltrimethylammonium chloride (GTMAC) as the quaternary ammonium reagent. Using Staphylococcus aureus and Escherichia coli as test strains, the antibacterial activity and underlying mechanisms were investigated. The results demonstrated that increasing the GTMAC feed ratio significantly enhanced the degree of substitution and surface positive potential of QPCPA, accompanied by improved water solubility but a slight reduction in thermal stability. QPCPA exhibited concentration-dependent bacteriostatic/bactericidal activity, with QPCPA-10 (DS = 0.962) possessing the highest degree of substitution displaying optimal antibacterial performance. Mechanistic studies confirmed that positively charged QPCPA electrostatically adsorbs to the negatively charged bacterial membrane, triggering membrane depolarization, intracellular Reactive Oxygen Species accumulation, membrane disruption, and massive leakage of nucleic acids and proteins, ultimately leading to bacterial death. This research establishes a facile modification strategy for constructing cationic antimicrobial polysaccharides from natural Poria cocos polysaccharides, demonstrating promising application potential in food preservation, antimicrobial biomaterials, and antibacterial coatings.