Screening Of High-yield Proteinase Lab Strain And Its Apptication In Hydrolyzing Milk Casein

Traditional fermented milk form common herdsmen’s house in Inner Mongolia were collected, and lactic acid bacteria (LAB) in samples were isolated and purified. Screening 12 LAB from the 63 LAB by the transparent circle, the first 36 h enzyme values were determined, The highest enzyme activity is 9.91 U/mL. Its higher protease activity strains identified and 16S rRNA homology analysis, the results showed that Identification with 16S rRNA indicated that homology reached 99% for LB2 with Lactobacillus delbrueckii subsp. bulgaricus strain, 1.8 with Lactobacillus salivarius subspecies salivarius,1.26 with rhamnosus Lactobacillus, homology reached 98% for R04 with Enterococcus faecium, and homology reached 97% for SY08 and Enterococcus faecalis.Response surface methodology (RSM) was employed to optimize the conditions of the ultrasonication to obtain the holoenzyme of lactic acid bacteria. The ultrasonic time、 ultrasonic power and lysozyme addition were studied for the effect on the ultrasonication. The prepared holoenzyme of lactic acid bacteria was investigated on skim milk and casein. Results indicated that the enzyme activity rose at first and then declined with the increase of ultrasonic power and ultrasonic time. The optimal ultrasonication conditions including ultrasonic time、ultrasonic power and lysozyme addition were determined to be 71%,7 min 30 s and 290μL, respectively. The holoenzyme obtained under these optimal extraction conditions, was used to hydrolysis skim milk and casein,test showed that the ultrasonication had a great impact on the loss of enzyme activity, when sonicating the cell separately, the amount of free amino acids in the hydrolysate of skim milk and casein were increased by 323.86% and 424.11%,respectively.Chromatographic analysis also proved that the obtained polypeptide hydrolysed by the holoenzyme also increased and showed diversity.