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The Research on Immobilization of ¦Â-galactosidase and Production Technology of Low Lactose Milk

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Tutor: ChengYunHui
School: Changsha University of Science and Technology
Course: Of Food Science
Keywords: ¦Â-galactosidase,immobilization,low-lactose milk,browning inhibition
CLC: TS252.4
Type: Master's thesis
Year:  2011
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Abstract:
Milk is the best natural food with rich nutrient. However, China is a place with high incidence of lactose intolerance and the probability of occurrence of lactase deficiency of children is also high. This situation is largely inhibits people¡¯s intake of milk and dairy products and blocked the development of China¡¯s dairy industry. While, the low-lactose milk not only can effectively solve the problem of lactose intolerance, but also will be a new economic growth point in the dairy industry. So it is important to study low lactose milk. In order to provide a theoretical basis and technical support for low lactose milk with high hydrolysis rate, this thesis focused on the determination of lactose in milk and dairy products, immobilization of¦Â-galactosidase and preparation techniques of low-lactose milk.Firstly,to determine a simple and accurate method to determine the content of lactose in dairy products, we comparatively studied the direct titration method, the antrone method and the iodometric method. Comparing linearity, precision and the maximum relative error of lactose¡¯s recovery of three methods, we selected the iodometric method to detect the lactose¡¯s content in dairy products.Secondly, we studied¦Â-galactosidase as the object, took sodium alginate-gelatin (SA-Gel), sodium alginate-carrageenan (SA-KC), sodium alginate-carrageenan-gelatin (SA-KC-Gel) as carriers and measured enzyme activity by glucose kit. The specific activity of immobilized enzyme and immobilized efficiency of enzyme were the indexes. The results were as follows in their best condition the specific activities of immobilized enzyme by SA-Gel, SA-KC, SA-KC-Gel were 31.89U/g, 76.42U/g, 48.53U/g and their corresponding immobilized efficiency were 25.49%, 76.40%, 48.52%. The optimum temperature of three immobilized enzyme were 50¡æ, 45¡æ, 45¡æ, but the free enzyme¡¯s was 40¡æ. The optimum pH all were 6.80, which were in the milk¡¯s natural pH range, and it would not have a negative impact on its hydrolysis. The left activities of three kinds of immobilized enzyme were more than 50 percent after being used six times greater. Combined with mechanical strength of the immobilized enzyme, we determined SA-KC-Gel is a new and effective carrier for immobilizing¦Â-galactosidase. Finally, the indicator of lactose hydrolysis rate was investigated by the iodometric determination. We produced low lactose milk by SA-KC-Gel immobilized lactase and free Lactozyme and the lactose hydrolysis rate were 70.02% and 92.67%. At the same time, we used HPLC method to detect the sugar in reconstituted milk and low lactose milk. Analysis results confirmed that more than 90% of lactose was hydrolysised by¦Â-galactosidase to glucose, galactose and galacto-oligosaccharide. Taking 5 - hydroxymethylfurfural as index detected by UV spectrophotometry, we developed a new effective compound browning inhibitor with 40% of anti-browning rate for low-lactose milk.
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