A Study on Extracting Gelatin from Bigeye Tuna (Thunnus Obesus) Skin: An Alternative to Mammalian Gelatin

Abstract

Gelatin is not a naturally occurring protein, obtained by partially hydrolysis of native collagen (Karim, and Bhat, 2009). It is a colorless or slightly yellow, nearly tasteless and odorless compound with translucent property. Gelatin is widely used in food, pharmaceutical, photographic and cosmetic industries (Karim and Bhat, 2009). Currently, gelatin is produced using beef bone, hide, and pig skin and pig bone. However, Bovine spongiform encephalopathy (BSE) disease as well as religious concerns is negatively affecting the gelatin market. There is also a high competition for this kind of mammalian sources among producers. Therefore, it is important to introduce alternative sources rich in collagen for production of gelatin. Fish skin, which is enriched with collagen, has a potential to be used for extraction of gelatin (Badii and Howell, 2006). Furthermore, fish skin is concerned as a major byproduct of the fish-processing industry, causing waste accumulation and pollution. Utilization of this collagenous fish waste minimizes environmental pollution, while it adds value to fish based by-product sector. For the present study, Bigeye tuna (Thunnus obesus) skin was used, since Bigeye tuna is one of the most commercially important tuna fishery resource in Sri Lanka. The study aims to extract fish methodology characterization of physical, chemical and functional properties of extracted gelatin. The cleaned fish skin samples were chopped in to small pieces and washed with running tap water for about 10 minutes. Six treatments with three different NaOH and H 2SO4 concentrations at two different time combinations were selected for final experiment after conducting preliminary experimental trials. First 30 g each of six samples were soaked in different concentrations of Sodium Hydroxide (w/v) for two different time combinations (S1- 0.1 % for 24 hrs, S2- 0.2 % for 24 hrs, S3 -0.3 % for 24 hrs,S4- 0.1 % for 36 hrs, S5-0.2 % for 36 hrs, S6- 0.3 % for 36 hrs) separately. Then each pretreated skin samples were rinsed with running tap water and allowed to drain using muslin cloth. Each partially treated sample was again treated with different diluted H2SO4 concentrations (w/v) for two different time combinations (S1-0.1 % for 24hrs, S2-0.2 % for 24 hrs, S3-0.3 % for 24 hrs, S4-0.1 % for 36 hrs, S5-0.2 % for 36 hrs, S6-0.3 % for 36 hrs) separately. Each treated skin samples were again rinsed with tap water and allowed to drain using muslin cloth separately. Treated samples with different acid, alkaline time combinations were performed using distilled water (1:2 w/v) in a water bath at 60 C for 05 hours for gelatin extraction separately. Finally, differently treated gelatin solutions were filtered through 2 layers of muslin cloth to remove residual skin parts and final products were oven dried at 90 C for 06 hrs.

Then the final products were analyzed for different parameters. Yield was expressed as a percentage (%) of the wet weight of the fish skin used. Gel strength was determined by using a Texture Analyzer (53205 Digital fruit firmness tester). The melting point was determined by preparing 6.67 % (w/v) gelatin solutions and maturating in a refrigeration temperature at 07 C for 16-18 hrs. Then melting points of final products were recorded by increasing the temperature in a water bath until the gelatin samples are dissolved (Karim and Bhat, 2009).