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Abstract

The anaerobic fermentation of waste prawn shell (Nephrops norvegicus) using lactic acid bacteria, in combination with especially selected proteolytic enzyme producing bacteria, has been established as an effective method for breaking down shell waste and isolating the valuable components contained within the shell structure. One of these components is the biopolymer chitin, which has numerous industrial applications and has traditionally been produced by a harsh chemical method which is extremely hazardous, energy consuming and ultimately damaging to the environment as it employs high concentrations of mineral acid and alkali. This qualitative study investigates the potential of prawn shell fermentation to provide a multi-product process, thereby eliminating waste and generating revenue. Fermentations were carried out in a bench-top, stirred tank bioreactor (5-litres). Various components of the fermentation product were analysed. The chitinous residues were characterised by CHN and calcium analysis. The composition of the protein mixture in the fermentation liquor was assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Two-dimensional SDSPAGE followed by mass spectrometry allowed remaining proteins in the liquor to be identified. Carotenoid pigments in the liquor, potentially applicable in animal feed supplements, were investigated for their extractability in various solvents. A fine, white precipitate that is formed in the fermentation broth was also examined.

Key results of the study showed that the unique microbial mixture used in the fermentation of prawn shell waste served to achieve the desired objectives i.e. (i) the production of a purified chitin with calcium removal as high as 93.8%; (ii) the production of a pigmented liquor containing peptides, amino acids only a few intact proteins. Sarcoplasmic calcium-binding protein was consistently found as a surviving protein in the fermentation broth. This study demonstrates the use of a biotechnological process as an alternative to the traditional chemical approach used in the manufacture of chitin. Trials have begun to assess the nutritive value of the liquor in lobster farming while biotransformation studies on bioprocessed chitin are ongoing.