Ultrasonic-assisted Acid Extraction And Physicochemical Properties Of Collagen From Soft-shelled Turtle Calipash

Collagen is the most abundant and widely distributed functional protein in mammals. It has good biodegradability, biocompatibility and biological activity, so it is widely used in food, medicine, cosmetic and other fields. In recent years, collagen derived from aquatic products has been widely recognized around the world for its safety. Soft shelled turtle has high protein content, low fat content, and its collagen content is very rich, so it can be used as a good source of collagen. The traditional methods of extraction of collagen were mainly concentrated in acid and alkali extraction, hot water extraction, physical extraction and enzyme extraction. This paper used ultrasound combined with acid extraction method to extract acid soluble collagen from the turtle skirt, not only can significantly improve the extraction efficiency, shorten the extraction time, but also can improve the yield of collagen,make full use of raw materials. The structure of the extracted collagen was intact, the purity of it was high, and the thermal stability was obviously better than that of other sources. In this paper, we studied the nutritional value and collagen content of soft shelled turtle skirt, and ensured it could be used as a good source of collagen; and then determined the process parameters of ultrasonic acid extraction of collagen protein; Finally, we compared the physical and chemical properties and functional characteristics of conventional extracted collagen (ASC) and ultrasonic acid extracted collagen (UASC). The main results are as followed:1. The nutritional value and collagen content of turtle skirt were studied. We used turtle skirt as raw material to conduct a comprehensive analysis and evaluation of nutrition. The results showed that the contents of water, crude protein, crude fat and ash were 70.1%, 28.3%, 0.22% and 0.95%, so turtle skirt meets the nutritional needs of low fat and high protein. And the content of amino acids in turtle skirt is rich,although it is not an ideal source of amino acids, but it is rich in collagen, so it can be used as a good source of collagen; In addition, turtle skirt also contains a variety of trace elements and major elements, the content of Zn and Se is high. Therefore, turtle skirt is a kind of food with high nutritional value.2. Extraction of collagen from turtle skirt with ultrasonic and acid. The results of single factor experiment showed that the ultrasonic time (min), ultrasonic power (W),and the ratio of material to liquid (g/mL) had a certain influence on the yield of collagen extracted by ultrasonic assisted acid extraction. In this study, the Box-Behnken design response surface method was used to establish the mathematical model between three factors and one response value,and the yield of collagen was optimized by the method of overlay contour. The influence degree of each factor on UASC is predicted by the prediction model: ultrasonic power (Xi) > material liquid ratio (X3) > ultrasonic time (X2); The optimum parameters of ultrasonic assisted acid extraction of collagen from turtle skirt were: 210.41W (ultrasonic power), 24.31min(ultrasonic time) and 1:20.70 g/mL(the ratio of material to liquid). Under these conditions, the yield of collagen was about 19.52%. The experimental results show that the model has good reliability.3. We used turtle skirt as raw material to compare the physical and chemical properties and functional characteristics of conventional extracted collagen (ASC) and ultrasonic acid extracted collagen (UASC). By means of Fourier transform infrared spectroscopy, circular two chromatography, UV spectra and SDS-PAGE analysis, we proved the purity of the collagen extracted by two methods is high and the structure was not damaged. Moreover, the thermal stability experiments showed that the thermal stability and heat resistance of UASC and ASC were significantly higher than those of other sources, and UASC was better than ASC, This makes the application of UASC wider than other collagen in food processing and medical materials field In addition, the functional properties of UASC and ASC were compared. The results showed that the solubility, emulsifying, foaming, oil holding and water holding capacity of UASC were better than those of ASC.