EXTRACTION AND CHARACTERIZATION OF GELATIN FROM NILE TILAPIA (OREOCHROMIS NILOTICUS) SKIN WASTES AND ITS APPLICATION AS STABILIZER ON YOGHURT

Abstract

Recovery of fish skin proteins existing in the by-product materials and using them as functional ingredients in food systems is a very exciting and promising alternative of mammalian gelatin. Fish skin is a byproduct of fish processing industry and can be converted into valuable product like gelatin. Gelatin is a soluble protein obtained by partial hydrolysis of collagen. Collagen is the main protein of animal tissues. The present study has focused on the production of gelatin from the Nile tilapia fish skins generated as byproduct in Arba Minch local fish processing industry and determination of the physicochemical characteristics of the obtained gelatin. The extraction of gelatin was carried out by a series of steps involving pre-treatment with 0.25% (w/v) sodium hydroxide and 0.3% (w/v) sulfuric acid, and 0.8% (w/v) of citric acid followed by a final extraction with distilled water at 55 °C for 12 hours. The gelatin was extracted successfully from tilapia skin and yield of 22.34 % was achieved. The extracted gelatin contained 10.92% moisture, 86.84% protein, 0.24% fat, and 0.42% ash contents, while gel strength, viscosity, WHC , FBC, melting point and the pH values were 228 g, 7.8 cP, 541 % , 2463%, 27.5 and 6.2, respectively. The obtained gelatin was characterized by FTIR and the spectra of the extracted gelatin were found to be similar when compared with commercial gelatin. FT-IR showed regions of amides A, B, I, II and III at 3401.64, 2926.40, 1634.47, 1500.46 and 1201.80cm-1 respectively. Based on obtained results fish gelatin can be considered as an excellent alternative to mammalian gelatin because of their similarity in functional properties with commercial gelatin. The extracted gelatin has been used as stabilizer in yoghurt preparations to improve the shelf- life and quality attributes. Four yoghurt samples were prepared with gelatin added at different concentrations (0.0%, 0.2%, 0.4% & 0.6%). The properties like titratable acidity, pH and % of syneresis were analyzed at every 3 days interval for the duration of two weeks. Gelatin added sample showed less syneresis compared to control and slowed the acid development in yoghurt during the storage period. Yoghurt with gelatin showed slight decreased of pH, while control yogurt highly decreased. The addition of extracted gelatin at 0.4% (w/v) in yoghurt gave good sensory acceptability with acceptable syneresis value, while the high concentration of gelatin at 0.6% (w/v) have significantly reduced % of syneresis, but it lead to very firm structure and also impaired palatability.