A PROCESS TO OBTAIN COLLAGEN, CHONDROITIN SULFATE AND CHITIN FROM FISH SKIN

Nile tilapia (Oreochromis niloticus) is one of the most farmed fish worldwide, and the processing wastes account for approximately 70% of the whole animal. Fish skin is a valuable by-product, and its utilization represents a better solution for the sustainability while adding value to the production chain, and are important source of bioactive molecules such as proteins and polysaccharides. In this work, a method for utilization of fish skin is proposed by extraction and production of biomolecules using simple steps.

Fish skin comprising of tegument and scales was obtained from local processing plants and immediately taken to the laboratory on ice, packed in plastic bags and frozen at -20°C until use. All steps were carried out in ice bath. The material (200 g wet skin) was thawed and grinded with 150mM NaCl solution (1L). The skin was defatted with 10% (v/v) butanol (2L) for 12 h, twice. The material was then added of 2L of 0.1M NaOH solution extraction of soluble non-collagenous proteins at 4°C, to obtain the "Alkaline extract". After that, the material was submitted to a 3-fold extraction with 1.5L of 0.2M acetic acid to obtain acid soluble collagenous proteins (Acid extract). Finally, the material was added of 1L distilled water and the pH was adjusted to 7.0, followed by heating to 80°C for 30 min to obtain soluble proteins (Heat extract). The residual solid material was dried in an oven at 50°C (Scale material). Biomolecules extracted (Fig. 1) were characterized by FT-IR, gel electrophoresis and the yield of each material was determined.

The method for utilization of Tilapia skin proved to be useful for extraction of many biomolecules, which can be used as alternative biomaterials for biomedical applications. The Alkaline extract was purified and used for preparation of a chondroitin sulfate-like glycosaminoglycan, which presented similar electrophoretic migration to mammalian glycosaminoglycans. The Acid extract contained collagenous proteins and SDS-PAGE revealed that the main component of Tilapia skin is possible Type-I collagen, and the residual non-soluble collagen was extracted as gelatin in the final process in the Heat extract. Chitin was found to be the main fibrous material present in the scales after all extraction, which can be used for chitosan preparation afterwards. The final yield of all components in 200 g of wet fish skin (aprox. 145 g dry weight) was 90 g of collagenous proteins, 7.5 g of crude gelatin, 5.0 g of crude chitin and 10 mg of chondroitin sulfate-like glycosaminoglycan. A complete characterization of these biomolecules is being carried out for future application as alternatives for mammalian-derived collagen and GAGs, as well as crustacean chitin, and possible biological activities as components in biomedical devices, new glycan drugs with anti-inflammatory and antithrombotic properties.