Statistical optimization of culture medium for neutral protease production by Streptomyces sp. using sardine viscera

Proteases are the most important industrial enzymes and widespread in nature. In the present work, sardine waste (viscera) was used to optimize the protease production by newly isolated Streptomyces sp. strain. A comparative study of proteolytic activity was first carried out on a synthetic medium, sardine waste broth (in submerged fermentation), and powder of the same waste (in solid-state fermentation). The enzyme production media were optimized according to statistical methods, while using two plans of experiences. The first corresponded to the Plackett-Burman matrices and the second was the Box-Wilson central composite design. The protease characteristics study showed an optimum temperature of 40 degrees C and an optimum pH of 7, which is a typical characteristic of neutral proteases. The results of protease production optimization showed maximum activity on the following fermentation medium: sardine viscera broth (25%), NaCl (7.99 g/L), and gelatin (9.82 g/L). All these results confirmed the high biotechnological potential of this strain for neutral protease production on sardine viscera, which provides an interesting and promising strategy for large-scale enzyme production on fish waste.