Optimization of Ultrasound-assisted Extraction and Structural Characteristics Analysis of Collagen from Chinese Giant Salamander(Andrias davidianus) Skin

Artificial-breeding salamander skin contains a lot of collagen. The yield of collagen extracted from the skin of salamander by conventional extraction method was low. In order to improve the collagen yield from the skin of salamander, the ultrasonic-assisted technology was used to treat the skin of salamander. The Box-Behnken design was used to optimize the process of ultrasonic-assisted enzymatic extraction of collagen from the skin of salamander. The effects of ultrasonic power, ultrasonic time and liquid-solid ratio on the collagen yield were investigated. Scanning electron microscopy(SEM), sodium dodecyl sulfate polyacrylamide gel electrophoresis, Fourier transform infrared(FT-IR) and amino acid analysis were used to characterize the collagen of salamander skin. The results showed that the optimal conditions of ultrasonic assisted extraction were as follows: ultrasonic power 201 W, ultrasonic time 26 min, liquid-solid ratio 21:1 mL/g. Under these conditions, the collagen yield of salamander skin was 37.36%±2.61(n=3), close to the predicted value of the model(37.76%), significantly higher than that of salamander skin collagen without ultrasonic treatment(17.56%±1.77%). Ultrasound assisted treatment increased the surface porosity of salamander skin, which was helpful for collagen dissolution. Collagen extracted from the skin of salamander was type I. Ultrasound treatment reduced the content of α-helix and β-turning angles, increased the content of β-folding, irregular coiling and β-anti-parallel folding in the secondary structural units of salamander skin collagen, and made the microstructure more dense, while the amino acid composition did not change significantly. This study would provide an effective method for industrial production of skin collagen of salamander, and would provide a reference for the subsequent development and utilization of artificial-breeding salamander resources.