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.
Highlights
Cheese-making and fermentation represent the first examples of applied biochemistry and biology (Fox, 1999)
The agar containing casein revealed that A. niger FFB1 exhibits a protelolytic activity indicated by the clear zone around the colony created after hydrolysis of casein to soluble peptides and amino-acids (Fig. 1)
Wheat bran in solid-state fermentation (SSF) allowed to evaluate the milk-clotting activity (35.7 ± 3.8 SU/mL) and the proteolytic one (1253.01 ± 145.07 μg/h/mL) of proteases produced by A. niger FFB1
Summary
Cheese-making and fermentation represent the first examples of applied biochemistry and biology (Fox, 1999). Aspartic proteases from fungal origin are inactivated at normal pasteurization temperatures and have low levels of non-specific proteolytic activity. The majority of these enzymes are mainly produced by genera such as Aspergillus, Mucor, Entothia, Rhizopus, Penicillium and Fusarium. Solid-state fermentation involves the growth of microorganisms on solid substrates in the absence or near absence of free water in the space between particles This low moisture content makes the SSF different from the submerged fermentation (SmF) (Manpreet et al, 2005). More consideration is given to topics related to cheese-making, where obtaining a low proteolytic activity compared to milk-curdling one must be respected
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