Abstract

Five species of Aspergillus fungus: Aspergillus niger, Aspergillus flavus, Aspergillus awamori, Aspergillus tubingensis and Aspergillus tamarii, and one Penicillium: Penicillium pinophilum were isolated from Algerian soil and identified using both microscopic observation and ICT sequence identification. Their potential milk-clotting activity was demonstrated and attributed to an acidic protease activity. For the culture and enzyme production from the six selected fungi, an approach compatible with sustainable development was developed. A whey (cheese industry secondary product) based culture medium was designed and optimised for each species using first Plackett–Burman and then Box and Wilson statistical experiments. The studied factors were pH, stirring, lactose, yeast extract, peptone, CaCl2 and salts: MgSO4 and FeSO4. Once the selected factors were optimised, the whey based fermentation mediums were used for the production of acidic protease. All molds were shown to be able to produce acidic protease directly in their culture medium and to generate milk clotting within 15 min. The only exception was A. awamori, which exhibits a good acidic protease activity but no clotting capability.

Key words: Acidic protease, Aspergillus, experimental design, milk-clotting enzyme, optimization, Penicillium.