Valorisationof microbial biodiversity : Characterization of a milk-clotting enzyme produced byBacillus velezensis FK6Astrain isolated from Algerian dairy farm soil in light of its usein the manufacture of hard cooked cheeses

Abstract

A strain known as FK6A, which produces a milk-clotting enzyme isolated from the soil of an Algerian dairy factory, was identified as Bacillus velezensis based on morphology and internal transcription spacer sequence. Phylogenetic and sequencing analysis of 16S rDNA gene showed a 100% identity match between the tested strainand the Bacillusvelezensis in the database (Code MH368142). This strain produced an active extracellular protease purified by partial purification using ammonium sulfate fractionation(40–80% saturation) followed by chromatography of molecular exclusion, which revealed the existence of tow active peaks. The optimal activity was observed at pH 5.7; 75°C and 40 mM of CaCl2. The clotting enzyme has been shown to be a metalloprotease inhibited by EDTA. The highly proteolytic activity of the Bacillus velezensis extracts observed on the curds appears a few minutes after the appearance of a firm coagulum reflected by the appearance of an abundant serum.Thus, to solve this problem and to inhibit proteolytic activity, the curds were cooked after brewing during the manufacturing process