Effect of Dosage on the Coagulation Performance of Bacillus velezensis Rennet

To study the coagulation performance of rennet from Bacillus velezensis DS-1, we evaluated the effect of its different dosages (9、12、15、18、21 and 24 U/mL) on the turbidity, viscosity, rheology, optical density at 500 nm (OD_{500 nm}) and microstructure of curd. To this end, commercial rennet was used as control. The results showed that when the rennet dosage ranged from 9 to 21 U/mL, the viscosity of coagulated milk initially increased and then leveled off, and the turbidity increased with increasing curdling time. When the rennet dosage was 24 U/mL, the turbidity increased at first and then decreased with increasing curdling time. The rheological characteristics showed that peak storage modulus of milk coagulated with rennet from strain DS-1 at dosages below 18 U/mL was smaller than that with commercial rennet and it gradually increased with increasing dosage of DS-1 rennet. As the dosage rose from 9 to 21 U/mL, the water-holding capacity increased significantly (P < 0.05). The OD_{500 nm} value declined first and then increased slightly with increasing rennet dosage. The microstructure analysis showed that casein particles were more densely with increasing rennet dosage, and milk curd formed by rennet from Bacillus velezensis DS-1 exhibited a more porous structure. The results of this study demonstrate that Bacillus velezensis DS-1 rennet has good coagulation performance, showing minimal differences in coagulation parameters compared with commercial rennet.