title: Effects of cryostabilizers, low temperature, and freezing on the kinetics of the pectin methylesterase-catalyzed de-esterification of pectin.
abstract: The kinetics of the pectin methylesterase (PME)-catalyzed de-esterification of pectin was studied at 25 degrees C in the presence of sucrose, fructose, maltodextrin (DE = 16.5-19.5), and carboxymethylcellulose at different concentrations and in the presence of maltodextrin and sucrose at different concentrations in a temperature range between +25 and -4 degrees C in subcooled and frozen states. The objective was to determine whether the reaction is diffusion-controlled, to gain insight about the factors determining the diffusion of the reactants, and to determine the effect of the carbohydrates, low temperature, and freezing on the structural conformation of the enzyme. The results indicate that the PME-catalyzed de-esterification of pectin is diffusion-controlled. Nevertheless, the diffusion is not controlled by the macroviscosity of the reaction medium, but rather by the microviscosity experienced by the diffusants. Low temperature in the temperature range studied does not affect the structural conformation of the enzyme, while freezing seems to have some effect.
authors.affiliation: Laboratory of Food Technology, Department of Food and Microbial Technology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.
authors.forename: Netsanet Shiferaw
authors.initials: NS
authors.lastname: Terefe
authors.forename: Mulugeta Admasu
authors.initials: MA
authors.lastname: Delele
authors.forename: Ann
authors.initials: A
authors.lastname: Van Loey
authors.forename: Marc
authors.initials: M
authors.lastname: Hendrickx
mesh_terms: D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D002266:Carboxymethylcellulose Sodium / Q000008:administration & dosage; D003080:Cold Temperature; D003451:Cryoprotective Agents / Q000494:pharmacology*; D004951:Esterification; D005615:Freezing; D005632:Fructose / Q000008:administration & dosage; D007700:Kinetics; D010368:Pectins / Q000378:metabolism*; D011134:Polysaccharides / Q000008:administration & dosage; D013395:Sucrose / Q000008:administration & dosage; D014783:Viscosity
chemical_list: D003451:Cryoprotective Agents; D011134:Polysaccharides; D005632:Fructose; D013395:Sucrose; C008315:maltodextrin; D010368:Pectins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase; D002266:Carboxymethylcellulose Sodium