Work

Purification and characteristics of a novel milk-clotting metalloprotease from Bacillus velezensis DB219

Year: 2023

Type: article

Abstract: Milk-clotting enzyme (MCE) is the essential active agents in dairy processing. The traditional MCE is mainly obtained from animal sources, in which calf rennet is the most widely used in cheese industry. Traditional MCE substitute is becoming necessary due to its limited production and increased cheese consumption. A novel traditional MCE substitute was produced from Bacillus velezensis DB219 in this study. DB219 MCE exhibited a notable specific activity of 6110 SU/mg and 3.16-fold purification yield with 28.87% recovery through ammonium sulfate fractionation and DEAE-Sepharose Fast Flow. The purified DB219 MCE was a metalloprotease with a molecular weight of 36 kDa. DB219 MCE was weak acid resistance and stable at pH 6.0–10.0 and temperature <45°C. The highest milk-clotting activity (MCA) was observed in substrate at pH 5.5 added with 20–30 mM of CaCl 2 . The Michaelis constant ( K m ) and maximal velocity ( V m ) for casein were 0.31 g/L and 14.22 μmol/min. DB219 MCE preferred to hydrolyze β-casein (β-CN) instead of α-casein (α-CN). DB219 MCE hydrolyzed α-CN, β-CN and κ-casein (κ-CN) to generate significantly different peptides in comparison with calf rennet and ES6023 MCE (fungal MCE) through SDS-PAGE and RP-HPLC analysis. DB219 MCE mainly cleaved Thr124-Ile125 and Ser104-Phe105 bonds in κ-CN and had unique casein cleavage sites and peptide composition through LC-MS/MS analysis. DB219 MCE was potential to be a new milk coagulant and enriched kinds of traditional MCE substitute.

Source: Journal of Dairy Science

DOI: 10.3168/jds.2023-23450