Solvent effects on quercetin incorporation, release behavior, and antibacterial efficacy in gelatin/dialdehyde cellulose composite films: A comparative study

Abstract

As quercetin has poor solubility in water, a solvent or surfactant is required to ensure its dissolution and homogeneous distribution within a biopolymer matrix. This study systematically compares the effects of two solvents, dimethyl sulfoxide (DMSO) and ethanol, on the physicochemical properties, quercetin distribution, release behavior, and antibacterial efficacy of gelatin/dialdehyde cellulose (GD) films loaded with quercetin. Films were prepared with quercetin dissolved in DMSO (GDQ-D) or ethanol (GDQ-E). Scanning electron microscopy images revealed that both quercetin-loaded films contained a mixture of rod-like and spherical quercetin formations; cross-sectional images showed a distinct dendrimer-like structure. FTIR analysis confirmed the presence of residual DMSO in GDQ-D, accounting for 25 ± 2.6 % of the initially loaded solvent. This residual DMSO constituted approximately 4–6 % of the total film weight. Its retention promoted a more homogeneous distribution of quercetin, minimized recrystallization, and enhanced antibacterial performance (achieving 77 % and 35 % reduction against S. aureus and E. coli, respectively). Conversely, ethanol evaporation during the film drying process led to densely packed quercetin aggregates in GDQ-E. This led to a significant reduction in quercetin release (2 μg/mL vs. 20 μg/mL in GDQ-D), thereby diminishing antibacterial efficacy (55 % reduction against S. aureus with no observable activity against E. coli). Overall, these findings demonstrate that solvent type and retained residue, quercetin morphology, and release kinetics collectively contributed to the observed functional properties.