Optimization of fermentation conditions for production of neutral metalloprotease by SCK6 and its application in goatskin-dehairing.

In this study, a high protease-producing strain was screened by spread plate method and identified by molecular biology and morphological identification. It was identified as sp. LCB14. A neutral protease gene was cloned and heterologous expressed by SCK6. Then, the recombinant protease was used to dehair the goat skins. The fermentation conditions of neutral protease production by SCK6 were optimized. The single factor experiments, Plackett-Burma experiment, and response surface method were conducted to determine fermentation medium and culture conditions. The optimized medium contained corn meal 49 g/L, soluble starch 28 g/L, soybean meal 17 g/L, corn steep liquor powder 8 g/L, yeast extract 10 g/L, NaHPO 2.3 g/L, KHPO 1.9 g/L, MgSO 0.5 g/L, MnCl 0.1 g/L and ZnSO 0.05 g/L. The optimized culture conditions were 35 °C and pH 7.0. Under the optimum conditions, the recombinant strain reached 33467.28 U/mL after 72 hr ferment. Moreover, by fed batch in 30 L fermenters, neutral protease production reached 39,440.78 U/mL and shortened fermentation time from 72 hr to 46 hr. Finally, the crude enzyme was utilized to replace sodium sulfide for dehairing of goatskins. The enzymatic dehaired pelts were white, smooth, and soft; the grain side of enzymatic dehaired pelts were clear; there was no obvious damage to the grain side of enzymatic dehaired pelts by visual observation and tactile test. Furthermore, there were no hair roots, hair follicles and other glands in enzymatic dehaired belts, and the collagen fibers of enzymatic dehaired belt were dispersed well by histological analysis.