Optimization of Method to Extract Collagen from "Emperor" Tissue of Soft-shelled Turtles

Soft-shelled turtles (Pelodiscus sinensis) are widely distributed in some Asian countries, and parts of this turtle contain abundant collagen. In this study, we optimized a method for extracting collagen from the soft-shelled turtle. We used three types of solvent and four extraction conditions to determine an effective collagen extraction method, which was extraction at 37°C with acetic acid after hydrochloric acid pretreatment. Next, we extracted collagen from three regions in the soft-shelled turtle: muscle, skin, and an area of soft tissue in the periphery of the turtle shell known in Japan and China as the "emperor." We determined that emperor tissue yielded the highest concentration and purity of collagen. We then optimized the pretreatment method for extraction from emperor tissue by using formic acid instead of hydrochloric acid, and the amount of extracted collagen increased by approximately 1.3-fold. Finally, we identified the optimal solvent out of four types of organic acid for collagen extraction from emperor tissue; the amount of extracted collagen from emperor tissue increased approximately 3-fold when citric acid was used as the extraction solvent instead of acetic acid. Emperor tissue can regenerate; thus, it is possible to obtain collagen from the emperor repeatedly without killing the turtle. Our findings suggest that the emperor tissue of softshelled turtles may be a good source of collagen for pharmaceutical and cosmetic applications.