Extraction, Characterization, and Antimicrobial Activity of Chitosan from Horse Mussel <i>Modiolus modiolus</i>

Abstract

Chitin and chitosan have been proved to have enormous applications in biomedical, pharmaceutical, and industrial fields. The horse mussel, <i>Modiolus modiolus</i>, a refuse of the fishery industries at Thondi, is a reserve of rich chitin. The aim of this work is to extract chitosan from the horse mussel and its further characterization using Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, X-ray diffraction (XRD), and elemental analysis. The result of FTIR studies revealed different functional groups of organic compounds such as out-of-plane bending (564 cm^-1), C-O-C stretching (711 cm^-1), and CH₂ stretching (1174 cm^-1) in chitosan. The degree of acetylation of the extracted chitosan was observed to be 57.43%, which makes it suitable as a biopolymer for biomedical applications. Prominent peaks observed with micro-Raman studies were at 484 cm^-1 (14,264 counts/s), 2138 cm^-1 (45,061 counts/s), and 2447 cm^-1 (45,636 counts/s). XRD studies showed the crystalline nature of the polymer, and the maximum peak was observed at 20.04°. Elemental analysis showed a considerable decrease in the percentage of nitrogen and carbon upon the conversion of chitin to chitosan, while chitosan had a higher percentage of hydrogen and sulfur. The antibacterial activities of chitosan from the horse mussel were found to be efficient at a 200 μg/mL concentration against all the bacterial strains tested with a comparatively higher antibacterial activity against <i>Escherichia coli</i> (9 mm) and <i>Bacillus subtilis</i> (8 mm).