Study On Screening Of High-Yielding Strains, Optimum Of Liquid Fermentation And Elemental Enzyme Properties

Systematic study on the screening of lactase-yielding strains, liquid fermentation of lactase high producing strain D2-26 and enzyme properties were carried out in this paper. The main results were as following:1. We improved tool of primary screening and found a reasonable method of repeated screening: using 0.2ml epondolf tube as new tool of primary screening; method of the second screening has three standards, including OHA, LHA and primary enzyme properties. The feasible assay procedure of lactase activity was put forward, namely using OHA and OHA/LHA represent LHA .The high-yielding strain D2-26 was screened by using ONPG as indicator from soil samples around production plant of Baoding Tensun Dairy CO.LTD, D2-26 showed relative high enzymatic activity in liquid fermentation, the OHA, LHA, OHA/LHA was 2.24U/ml, 1.71U/ml, 1.31 respectively. Optimal temperature was 70 ℃, optimal pH was 4.0. The enzyme had a good thermostability (70℃,10min). After primary identification the lactase-producing organism was identified as Aspergillus niger and safety strain.2. Optimized culture medium in liquid fermentation were: pectin 0.5%, corn liquor 2%, soybean powder 1.5%, N^NOs 0.2%, K2HPO4 1%, NP-5 0.3%. Optimized culture condition were:104 spore per mil inoculum quantity, pH5.5, 30癈,140rpm, 30/250mL. After optimum of liquid fermentation, the maximum enzyme activity of D2.26 was 6.53 U/ml.3.The test of crude enzyme indicated that optimal temperature of D2.26 lactase was 70 ℃, reaction temperature was relatively extensive. The lactase had good thermostability up to 70℃ and was higher temperature lactase. Optimal pH was 4.0 and it was stable at pH 2.5-7 at room temperature. The metal irons K+, Ca2+, Zn2+, Mg2+, Pb2+, EDTA have no inhibition on lactase .Fe2+, Cu2+, Mn2+ had different activation,Fe2+ has high activation at low density while Cu2+, Mn2+ have high activation at high density.