Extraction Of Crude Collagen From Pterygoplichthys Pardalis Skin

Fish play an important role in daily diets as well as malnutrition and it is a major source of high quality proteins (Jabeen and Chaudhry, 2011). Since early times, fish proteins have acted as a source which provided a high nutritional value for human health. Moreover, they have a higher protein content than most land-animal meats and are highly digestible, rich in several peptides and essential amino acids (Khalili Tilami et al. , 2018). Methionine and lysine are essential amino acids which are limited to those terrestrial meat proteins (Tacon and Metian, 2013). Therefore, demand for fish consumption has increased from 9 kg per capita in 1961 (FAO) to 20. 3 kg per capita in 2016 as the latest information (FAO, 2016). Among those proteins in fish, collagen is a most abundant protein which constitutes 30% of total proteins (Jongjareonrak et al. , 2005). It is a fibrous protein which acts as the principal constitute of fish skin, bone, fin and connective tissue (Karim and Bhat, 2009).

Collagen has excellent biocompatibility, biodegradability properties (Zhang et al. , 2009) and properties like well characterized low antigenicity (Li et al. , 2004) which tend to be used in many industrial applications in leather and film industry, cosmetics and pharmaceutical industries (Kittiphattanabawon et al. , 2005). In addition to those, collagen has potential to be used as a food additive and a biomedical material as an alternative source to mammalian collagens (Nagai and Suzuki, 2000). As the main source of industrial collagen from skins and bones has limited to those land-based animals such as pigs and cattles (Jongjareonrak et al. , 2005). But, there is a contamination risk in Bovine and porcine skins which might carry pathogens from diseases like Bovine Spongiform Encephalopathy (BSE) (Sotelo et al. , 2016), Transmissible Spongiform Encephalopathy (TSE) and Foot and Mouth Disease (FMD) (Jongjareonrak et al. , 2005). Additionally, collagen cannot be used at present for industrial applications which are obtained from pigs and cattle due to some religious constraints (Widyasari and Rawdkuen, 2014) and some aesthetic objections (Jongjareonrak et al. , 2005, Widyasari and Rawdkuen, 2014). Therefore, consumers are seriously considering about the consumption of collagen related products mainly from bovine and porcine skins. So, the attention towards safe alternative sources especially like fish collagens from marine and freshwater fish species have increased (Jongjareonrak et al. , 2005).

Many researches on extraction of collagen from fish skins in marine species have been carried out, mainly from marine species as Black drum, Brownstripe red snapper and Ocellate puffer fish in recent years. However, isolation of collagen from freshwater fishes except for the Nile perch, Grass carp and Channel catfish has been rarely reported (Zhang et al. , 2009). Pterygoplichthys pardalis is a freshwater species (Hubilla et al. , 2008) which was introduced to Sri Lanka in 1996 as an ornamental fish. The entry of this species was facilitated through the introduction of the macroeconomic policies by the Sri Lankan government in late 1970s (Marambe et al. , 2011). After the deliberate introduction have been made for the purpose of ornamental fish industry, P. pardalis escaped to the natural ecosystems due to the negligence and then, became a threat to endemic fish and inland aquaculture in Sri Lanka (Wijethunga and Epa, 2008). According to available records, there are some identified problems of this species as they are superior competitive because of their feeding behaviours, over population by their rapid growth (Bambaradeniya, 2002) and replace target fish in the reservoirs, destruction of fishing nets and absence of natural predators due to their hard bony external structure (Wijethunga and Epa, 2008) and they pollute their habitat quality (Marambe¹ et al. , 2011).

These factors have accelerated them becoming an Invasive Alien species (IAS). Even though many researches have been carried out for the development of value added products by using this species, factors like high ash and heavy metal concentrations present in their flesh, poor appearance of the fish, difficulties in processing and low flesh yield of the fish have limited their market utilization and direct consumption of this fish species. When fish skin is considered as a wastage, it represents 30-55% of the total body weight of a fish (Sotelo et al. , 2016). Many collagen proteins present in fish skin and fish collagen hydrolysates extracted from fish skins have many functional properties such as anti-oxidative properties, antimicrobial properties and metal chelating properties which are important in food industries (Jiang et al. , 2014). Therefore, these findings can be used in functional foods and medication as commercial applications similar to fish collagens. Thus, the aim of this research is to develop a simple, non-toxic and cheap method to extract crude collagen from Pterygoplichthys pardalis fish skin and to check the functional properties of its hydrolysates as the best solution for their overpopulation by utilizing their skin collagen hydrolysates for commercial applications.