Selection And Immobilization Of Lactase And Its Application In Milk For Reducing Lactose

Milk is characterized by rich nutrients,mellow taste,which is suitable for people at different ages.However,after drinking milk,many persons have abdominal pain,abdominal distension and diarrhea and other symptoms.It is probably due to the low content of lactose in human body or lactose intolerance attributed to lactase deficiency.Therefore,it is necessary to study the production of low-lactose milk with high quality and low price.In this study,optimal lactase was selected from three different factories.In the meantime,the resulting lactase was immobilized by different carrier agents using various methods.The activity and using time of immobilized lactase were evaluated.Furthermore,the process parameters to produce immobilized lactase was optimized.The cleaning,sterilization and repeating using rate were investigated.Through immobilized lactase hydrolysis,low-lactase milk with the hydrolysis rate higher than 70%was obtained.In addition,the cost can be reduced through using immobilized lactase for many times.The main results are shown as follows:(1)Through market survey and primary screening investigation,beta galactosidase from Chuke Hansen(Denmark),Harbin Meihua biotechnology,Shanxi Enzebiotechnology company were selected.After determination of enzyme activity,lactose hydrolysis efficiency and optimum pH range,it was found that a free beta glycosidase produced by Hansen(Denmark)had the glycosidase activity of 5005 U/g and its optimal pH range was 6.0-7.0.After hydrolysis at 37?±2? for 2-2.5 h,more than 98%of lactose in milk was hydrolyzed.Compared to the lactase produced by other two companies,lactase produced by Hansen was characterized by high enzyme activity,wide pH range,high hydrolysis rate and relatively low price.(2)Using food-grade sodium alginate as the immobilization carrier,the immobilization of selected lactase was carried out.4%sodium alginate water solution was mixed with enzyme at room temperature and the mixture was incubated for 0.5 h.After that,1%calcium chloride solution was added.The mixture was incubated for another 1h to obtain the immobilized enzyme.The optimal temperature of the resulting immobilized enzyme was 37?+2? and the optimal pH was 6.0-7.0.The enzyme activity was high and the mechanical properties were also satisfactory.(3)Four detecting methods were compared using the same milk sample.Specifically,HPLC,iodine value method,glucose reagent box method and Foss component analyzer were used.The hydrolysis effectiveness of lactase was used as the detecting parameter.In terms of detecting accuracy,efficacy and cost,the time needed for the Foss component analyzer was 10 min and the absolute difference value between two samples was 0.06%.Analysis using Foss component analyzer for detection of hydrolysis rate had several advantages,such as fast,convenient,accurate and stable.However,the detection cost was high.(4)The immobilized lactase was added to milk to reduce lactose in an industrial scale.More than 70%of lactose was hydrolyzed if the temperature was 37?±2?and hydrolysis time was 2.0-2.5h.Immobilized lactase was first cleaned using 3.0-5.0%H2O2.Next,it was sterilized by ozone at 10-20 ppm for 60 min.In this case,the immobilized lactase can be used for 5 times.