Bioconversion of Indian White Prawn (Fenneropenaeus indicus) Shell Waste into Chitosan: FTIR Structural Characterization and Antibacterial Activity against Escherichia coli and Staphylococcus aureus

Crustacean shell waste from seafood processing is a major environmental concern, although it constitutes a rich source of chitin and its deacetylated derivative, chitosan. This study aimed to extract and characterise chitosan from the shell waste of Indian white prawn (Fenneropenaeus indicus) and evaluate its antibacterial activity. Prawn shell powder (10 g) was subjected to sequential demineralisation, deproteinisation, decolourisation, and deacetylation. Characterisation of the recovered chitosan was performed by Fourier-transform infrared (FTIR) spectroscopy (400–4000 cm⁻¹), and its antibacterial activity against Escherichia coli and Staphylococcus aureus was assessed at 0.5% and 1% (w/v) concentrations using both disc and agar well diffusion assays. The extraction yielded 2.3 g of chitosan from 10 g of shell powder (23% yield). The FTIR spectrum confirmed the characteristic chitosan profile, with absorption bands at 3435.7 cm⁻¹, 2921.5 cm⁻¹, 1653.0 cm⁻¹, and 1152.6/1076.1 cm⁻¹. Antibacterial activity was concentration- and method-dependent: zones of inhibition ranged from 10 mm (0.5%, disc diffusion) to 33 mm (1%, well diffusion) against E. coli and from 10 mm to 46 mm against S. aureus, with the largest zone (46 mm) recorded for S. aureus treated with 1% chitosan by the well diffusion method.