| Microbial lipases, as results of its higher hydrolysis,esterification and transesterification have been widely employed in lipid synthesis, biodiesel and enantioseparation. Because of its poor stability and other factors, the scope of application of microbial lipases in feed industry was relatively narrow. The laboratory have constructed a new lipase from the ysast Yarrowia lipolytica, and obtained lipase preparations with higher stability in the appropriate role of protecting agent. The paper studies the enzymatic properties by comparison of four kinds of microbial lipases from different sources, and in vivo effect of Yarrowia lipolytica lipase on growth performance, lipid metabolism and safety assessment during broiler feeding. The main work and results are as follows:1 For the four different sources of lipases, including Yarrowia lipolytica lipase (YLL),Candida rugosa lipase (CRL), Thermomyces lanuginosus lipase (TLL) and Rhizopus oryzae lipase (ROL), a contrastive analysis were performed, according to their optimum temperature,pH, the thermal and pH stability. And then, the substrate specificity and kinetic parameters of YLL were studied. Results showed that the optimum temperature of.YLL was 40?. After 2 h of incubation at 30? and 40?, YLL has the best stability, with which residual activity was about 85% and 80%, respectively; Also, effect of pH values in the range of 2-9 by comparation of four lipases was studied, YLL show the best stability at low pH. After 2 h of incubation in lower pH 5, the residual activity was above 50%.YLL has the optimal substrate towords p-nitrophenyl palmitate (C16). It has a better hyydeolysis degree when used the long chain monoglyceride (C14, C16, C18) as substrate.2. We studied the optimal conditions during the process of in vitro hydrolysis of soybean oil. the hydrolysis degree under different time course, comprehensive evaluation of conversion efficiency of lipase additive on soybean oil. The optimum reaction conditions for the hydrolysis of soybean oil were: reaction time, 6 h, temperature, 40? ,enzyme concentration of 600 U, the ratio of water to oil, 3:1. We got two YLL preparations with protection by spray drying, and in vitro qualitative and quantitative analysis of production during enzymatic hydrolysis process was studied. The two formulations exhibited good stability, with 55% and 48% of residual activity after 2 h of incubation, respectively. Formula A (YLL+20% skim milk) has the best stability. Using animal feed as substrate, adding the same enzyme activity of YLL supernatant and preparations, detection of the main fatty acids has been enmerged after 6 h of reaction by gas chromatograph. Results suggested that YLL preparations show the higher hydrolysis degree compared to the free enzyme, in which, for C18:2, formulation A and B reached 65% and 58%, respectively.3. Effect of Yarrowia lipolytica lipase on feeding performance in white feather broiler was carried out. We studied the effect on growth performance and blood biochemical index during the feeding program. Also, the changes of intestinal microflora were studied. The results showed that the addition of lipase significantly decreased the feed conversion ratio(FCR, P < 0.05), increased serum triglyceride levels.4. Futhermore, we carried out a comprehensive assessment of lipase and single cell protein additives on feed safety in broilers. The results showed that compared with the control group and other groups, the slaughter rate, eviscerated rate, breast muscle rate, leg muscle rate,abdominal fat rate and viscera index did not show significant differences, which showed better feeding safety. |
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