15C-25 |
Thermal and biochemical characterization of an hyperthermophilic b-glycosidase for lactose hydrolysis in milk |
C. CRUZ-HERNANDEZ1, A. E. Cruz-Guerrero2, R. M. Cruz-Hernandez3, F. Mijangos-Santiago3, L. Gomez-Ruiz2, and M. Garcia-Garibay2. (1) Univ. of Guelph, Dept. of Food Science, Guelph, ON N1G 2W1, Canada, (2) Universidad Autonoma Metropolitana-Iztapalapa, (3) UNAM-FES Zaragoza The role of milk in nature is to nourish and provide immunological protection. It is not surprising, therefore, that the nutritional value of milk is high. In addition, milk is extensively utilized as an ingredient in the manufacture of a wide variety of products. Lactose, or milk sugar, is relatively insoluble and thus a problem in many dairy products. Some people lack the lactase b-D-galactosidase) enzyme, which splits lactose in the stomach. Hence they cannot digest lactose, or dairy products containing lactose. Our objective was to determine the thermostability and some biochemical parameters of the hyperthermophilic b-glycosidase commercially prepared by Recombinant BiocatalystTM Inc., and to assay its application in milk. By simulating pasteurization and ultrapasteurization conditions, the thermostability of b-glycosidase and a commercial lactase, were evaluated by differential scanning calorimetry (DSC), and by enzymatic activity (rate of release of glucose from lactose 5% in 0.1M phosphate buffer, pH 6.6, 90°C). Km, Vmax, optimum pH, and the activation energy (Ea) were also determined. The potential of the enzyme was determined using milk as a substrate. Compared to the commercial lactase used, the b-glycosidase proved to be more thermally stable and maintained its activity after being heat at pasteurization and ultrapasteurization temperatures. The specific activity was 1,965.33UE/mg of protein; Km and Vmax were 234.41 mM (8.16%) and 102.77 mmol/mL min respectively. Optimum pH was 4.5 and the Ea was 7.69 cal/mol. The enzymatic activity of the b-glycosidase was higher using milk as a substrate than using 5% lactose in buffer, and at higher temperature. The presented findings demonstrate the high thermal stability of this enzyme and the potential of to use the DSC technique to measure thermostability of these types of materials. Important characterization of b-glycosidase was described. These results suggest the feasibility of using b-glycosidase to hydrolyze lactose in milk at pasteurization and ultrapasteurization temperatures.
Session 15C, Dairy Foods
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