Optimization of conditions for extraction of acid-soluble collagen from grass carp (Ctenopharyngodon idella) by response surface methodology

Grass carp is a freshwater fish species widely known by consumers over the world. Its skin has abundant collagen which possesses many healthy effects. The optimal conditions for collagen extraction were determined by response surface methodology in this work. Box–Behnken design was applied to evaluate the effects of three independent variables (acetic-acid concentration, temperature and time) on the acid-soluble collagen yield of grass carp skin. Correlation analysis of the mathematical-regression model indicated that quadratic polynomial model could be employed to optimize the extraction of acid-soluble collagen. From response surface plots, acetic-acid concentration, temperature and time exhibited interactive effects on the extraction of acid-soluble collagen. The optimal conditions to obtain the highest acid-soluble collagen yield of grass carp skin were an acetic-acid concentration of 0.54 M, a temperature of 24.7 °C and a time of 32.1 h. Under these optimal conditions, the experimental values agreed with the predicted values, using analysis of variance, indicating a high goodness of fit of the model used and the success of response surface methodology for modeling extraction of acid-soluble collagen from grass carp skin.Industrial relevanceGrass carp is a freshwater fish species with important economic significance. The annual production of grass carp in China was 3.86 million tons in 2005 which was the highest among all the freshwater fish species (http://www.agri.ac.cn/DataIss/ZY/QT/200610/17688.html). The weight of skin accounts for approximately 9% of whole fish. It is interesting to find a way to improve its value. In this work, collagen was extracted from grass carp skin by acetic acid and a mathematical model of extraction was built by response surface methodology. The effects of acetic-acid concentration, extraction time and temperature were under investigation. The results showed that there is an optimal condition to obtain the highest collagen yield. The optimal condition was determined to be an acetic-acid concentration of 0.54 M, a temperature of 24.7 °C and a time of 32.1 h. This research is helpful to develop a new product using grass carp and to fully use this sort of fish resource.