OPTIMIZATION OF MILK-CLOTTING PROTEASE PRODUCTION BY A LOCAL ISOLATE OF ASPERGILLUS NIGER FFB1 IN SOLID-STATE FERMENTATION

Abstract

The need to surmount the limitation of obtaining rennin, has been actively pushed researches to find new substitutes that present high milk-clotting activity which enables the production of high yields of cheese. In this study, the production of extracellular milk-clotting protease by locally isolated fungal specie, Aspergillus niger FFB1 under solid-state fermentation (SSF) using cheep agro-industrial byproduct (wheat bran) was optimized. The effects of several physicochemical and environmental factors were investigated to select the optimal conditions that ensure the best milk-clotting activity by application of "One-factor-at-a-time" method. A trial of cheese production using the crude extract was also carried out. The maximum enzyme activity (830 SU/g bran with a ratio MCA/PA of 4.25) was obtained under the optimum conditions of temperature (30°C), spores concentration (106 spores/mL), incubation time (72 hours), and moisture content of solid substrate (39.2%) adjusted suitably with mineral solution (Czapek-Dox) of pH 4.