title: Stability and catalytic activity of alpha-amylase from barley malt at different pressure-temperature conditions.
abstract: The impact of high hydrostatic pressure and temperature on the stability and catalytic activity of alpha-amylase from barley malt has been investigated. Inactivation experiments with alpha-amylase in the presence and absence of calcium ions have been carried out under combined pressure-temperature treatments in the range of 0.1-800 MPa and 30-75 degrees C. A stabilizing effect of Ca(2+) ions on the enzyme was found at all pressure-temperature combinations investigated. Kinetic analysis showed deviations of simple first-order reactions which were attributed to the presence of isoenzyme fractions. Polynomial models were used to describe the pressure-temperature dependence of the inactivation rate constants. Derived from that, pressure-temperature isokinetic diagrams were constructed, indicating synergistic and antagonistic effects of pressure and temperature on the inactivation of alpha-amylase. Pressure up to 200 MPa significantly stabilized the enzyme against temperature-induced inactivation. On the other hand, pressure also hampers the catalytic activity of alpha-amylase and a progressive deceleration of the conversion rate was detected at all temperatures investigated. However, for the overall reaction of blocked p-nitrophenyl maltoheptaoside cleavage and simultaneous occurring enzyme inactivation in ACES buffer (0.1 M, pH 5.6, 3.8 mM CaCl(2)), a maximum of substrate cleavage was identified at 152 MPa and 64 degrees C, yielding approximately 25% higher substrate conversion after 30 min, as compared to the maximum at ambient pressure and 59 degrees C.
authors.affiliation: Department of Food Biotechnology and Food Process Engineering, Berlin University of Technology, Koenigin-Luise-Str. 22, D-14195 Berlin, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Buckow
authors.forename: Ulrike
authors.initials: U
authors.lastname: Weiss
authors.forename: Volker
authors.initials: V
authors.lastname: Heinz
authors.forename: Dietrich
authors.initials: D
authors.lastname: Knorr
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002384:Catalysis; D003198:Computer Simulation; D002523:Edible Grain / Q000201:enzymology; D004789:Enzyme Activation; D004795:Enzyme Stability; D001467:Hordeum / Q000201:enzymology*; D007700:Kinetics; D008956:Models, Chemical; D010936:Plant Extracts / Q000737:chemistry*; D011312:Pressure; D012639:Seeds / Q000201:enzymology*; D013696:Temperature; D000516:alpha-Amylases / Q000737:chemistry*
chemical_list: D010936:Plant Extracts; D000516:alpha-Amylases; D002118:Calcium