Optimization Of The Extraction Methods Of Tilapia Skin Gelatin And Characterization Of Its Physicochemical Properties

Gelatin,as a natural protein, because of its unique functional and rheological properties, it has been widely used in food, pharmaceutical, cosmetics and photographic industries. Mammalian gelatin (such as bovine gelatin and porcine gelatin) is the most popular and most widely used gelatin. However, due to the socio-culture and health factors, the use of Mammalian gelatin has raised various concerns among consumers all over the world. Some of these are tied to Judaism, Islam, Hinduism and other religious and vegetarians, who refuse to eat mammalian gelatin. Fish gelatin and porcine gelatin showed similar characteristics, while fish gelatin is acceptable to the religious people and the vegetarian, all of which makes it possible for use it as the substitute of the mammalian gelatin in food products.In this study, tilapia skin was pretreated with different types and concentrations of acids prior to extraction of tilapia skin gelatin. The difference of extraction rate, hydroxyproline content, protein distribution and viscosity of extracted gelatin as affected by the types and concentrations of acids were studied. Subsequentlly.physical and chemical properties including the textural characteristics,amino acid composition and vicosity as well as rheological properties of fish gelatin extracted under optimal conditions were tested. This study could not only be served as a technical reference for the utilization of fish processing waste, but also provide a theoretical basis for industrial production of tilapia skin gelatin and the possibility of using fish gelatin as an alternative to traditional cowhide and pigskin gelatin.Optimization of the extraction methods of tilapia skin gelatin. The experimental results show that the gelatin protein extraction rate is strongly affected by H+concentration in solution. The tilapia skin protein extraction rate pretreated by acetic acid, citric acid and hydrochloric acid were13.50%and20.55%,10.52%to20.01%and4.32%to20.86%, respectively. The highest rate of protein extraction and hydroxyproline content were close under the optimal acid treatment conditions, while the corresponding viscosity were different. Gel electrophoresis showed that the a-chain and (3-chain were mainly existed in gelatin and gelatin with a higher content of a-chain has better viscosity properties. Best quality of the extracted gelatin were acquired with acetic acid concentrations of0.15mol/L (pH=2.79), citric acid of0.05mol/L (pH=2.22) and hydrochloric acid of0.03mol/L (pH=1.52), among which acetic acid treatment was the best.Study of rheological properties of tilapia gelatin. The experimental results show that in the cooling phase of tilapia gelatin, the storage modulus G', loss modulus G" decreased with the increase of Na+and Ca2+concentration, while the storage modulus G', loss modulus G" increase with the increase of gelatin concentration. Phase angle8tended to the low-temperature offset with the increase of Na+and Ca2+concentrations. Tilapia gelatin gel temperature and melting temperature decreased with the increase of Na+and Ca2+concentration while increase with the increase of gelatin concentration. Under gelatin concentration of6.67%, tilapia gelatin gel temperature and melting temperature were relatively higher than or close to the cowhide and pigskin gelatin temperature reported in references.Study of materialized and textural properties of fish gelatin. In the tests of the physical-chemical properties, the viscosity of gelatin decreased with the increase of temperature, while increases with increasing of gelatin concentration. The viscosity of gelatin with concentrations of1%and2%changes significantly with the temperature change. In the tests of textural properties, gel strength of6.67%(W/W) gelatin was464.925±0.651g, which was higher than fish gelatin and mammalian gelatin gel strength reported in the literatures. It belongs to high gel strength gelatin. Gelatin rupture strength showed a trend to decrease after the first increase with the increase of Ca2+concentration. Gelatin textural characteristics of hardness, cohesiveiness, springiness and chewiness were reduced with the increase of Ca2+concentration. It showed great potential of using tilapia gelatin as alternatives to mammalian gelatin applied in food products, meanwhile in the process of gelatin, the amount of gelatin and salt added should be controlled in order to obtain gelatin products with good stability and excellent quality.