Sustainable and Integral Valorization of Dosidicus gigas Pen Waste: Combined Production of Chitosan with Antibacterial Properties and Human and Marine Probiotics

This study details a biorefinery approach to valorize <i>Dosidicus gigas</i> squid pen waste. The process starts with the enzymatic deproteinization of squid pens, which prove effective with both Alcalase and Novozym, with the latter exhibiting a slightly higher efficiency to yield a material with 73% chitin content. Subsequent alkaline hydrolysis produces highly deacetylated chitosan (>90% degree of deacetylation), followed by controlled depolymerization to obtain polymers with molecular weights ranging from 50 to 251 kDa. Both native and depolymerized chitosan exhibit antimicrobial activity against <i>Escherichia coli</i> and <i>Bacillus cereus</i>, with <i>B. cereus</i> demonstrating greater resistance to chitosan compared to <i>E. coli</i>. The research also explores the bioconversion of deproteinization and deacetylation effluents. Deproteinization effluents prove superior in sustaining microbial growth, supporting comparable growth and lactic acid production for human probiotic strains (<i>Lactobacillus plantarum</i> and <i>Leuconostoc mesenteroides</i>) when substituting commercial peptones. Marine bacteria (<i>Pseudomonas fluorescens</i> and <i>Phaeobacter</i> sp.) show lower productivity. Integrating these processes into a biorefinery framework enables the conversion of 1 kg of dry squid pens into 350 g of chitosan, and facilitates the production of 937-949 g of lactic acid using human lactic acid bacteria cultures in media formulated with squid pen-derived effluents, glucose, yeast extract, and mineral salts. This integrated approach highlights the potential for maximizing resource utilization from squid pen waste, reducing environmental impact and generating high-value bioproducts.