Biotechnological utilisation of Nephrops shell waste
Shellfish processing results in the disposal of large quantities of waste to landfill sites. This project sought to deal with the issue of the processing of marine crustacean waste, specifically that of the prawn, Nephrops norvegicus. The exoskeleton of Nephrops norvegicus contains chitin, β-(1→4)-N-acetyl-D-glucosamine. In this study shell waste was demineralised, via lactic acid fermentation, using a commercial silage inoculant. The product contained 11.2% (w/w) ash, 31.1% (w/w) protein and 53.5% (w/w) chitin. Addition of the proteolytic enzyme, bromelain and a nitrogen source to the fermentation system led to deproteinisation and further demineralisation of the shell. The final product contained 4.2% (w/w) ash, 5.3% (w/w) protein and 79.6% (w/w) chitin. Chitin is relatively inert but can be converted to its more reactive derivative, chitosan, by deacetylation. Chitosan, prepared from bioprocessed shell waste, was investigated as a potential coating for urinary catheters. Attempts are currently being made to prevent blockage of these biomedical devices due to mineral ions, via the use of different manufacturing materials. Shell waste that had been demineralised using lactic acid fermentation was deacetylated using 50% (w/v) NaOH at 90oC. Membranes were prepared from the resultant chitosan. After immersion in a bath containing artificial urine, adherence of calcium and magnesium ions to the membranes was measured and compared with adherence of the same ions to polyurethane membranes. Adherence of calcium to the chitosan membranes was not higher than adherence to the polyurethane control membranes. Adherence of magnesium ions was significantly less than to the polyurethane control. The chitosan was hence shown to have potential for use as a coating for urinary catheters.