Extraction, Characterization, and Antimicrobial Activity of Chitosan from Horse Mussel Modiolus modiolus

Chitin and chitosan have been proved to have enormous applications in biomedical, pharmaceutical, and industrial fields. The horse mussel, Modiolus modiolus, 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 Escherichia coli (9 mm) and Bacillus subtilis (8 mm).