Microwave-assisted carboxymethylation of guar gum improves antioxidant and antibacterial activity

Guar gum (GG), a naturally occurring polysaccharide derived from Cyamopsis tetragonoloba, possesses notable physicochemical and biological properties, but its practical applications are limited by poor solubility, instability, and microbial susceptibility. In this study, microwave-assisted carboxymethylation was employed to efficiently modify GG, yielding carboxymethyl guar gum (CMGG) with a high degree of substitution (DS = 0.64) in 15 minutes. Fourier-transform infrared, proton and carbon-13 nuclear magnetic resonance analyses confirmed functionalization by incorporation of carboxymethyl groups, with a distinct carboxyl peak at 1723 cm⁻¹ and a new signal at δ 184.2 ppm corresponding to the carbonyl carbon. Additionally, X-ray diffraction, scanning electron microscopy and thermogravimetric analysis revealed increased crystallinity, morphological alterations including the formation of smaller aggregates and a spongy-like texture, and improved thermal stability. CMGG demonstrated significantly increased antioxidant activity (IC₅₀ = 4.78 ± 0.12 mg mL⁻¹) and exhibited pronounced antibacterial effects against Bacillus cereus, Streptococcus thermophilus, Staphylococcus aureus, and Escherichia coli, outperforming native GG. Molecular docking simulations indicated potential inhibitory interactions between CMGG and dihydropteroate synthase, suggesting a possible mechanism for its antimicrobial activity. Overall, CMGG emerges as multifunctional, biocompatible material with promising potential for biomedical, pharmaceutical, and industrial applications.