title: β-galactosidase stability at high substrate concentrations.
abstract: Enzymatic synthesis of galacto-oligosaccharides is usually performed at high initial substrate concentrations since higher yields are obtained. We report here on the stability of β-galactosidase from Bacillus circulans at 25, 40, and 60°C in buffer, and in systems with initially 5.0 and 30% (w/w) lactose. In buffer, the half-life time was 220 h and 13 h at 25 and 40°C, respectively, whereas the enzyme was completely inactivated after two hours at 60°C. In systems with 5.0 and 30% (w/w) lactose, a mechanistic model was used to correct the oNPG converting activity for the presence of lactose, glucose, galactose, and oligosaccharides in the activity assay. Without correction, the stability at 5.0% (w/w) lactose was overestimated, while the stability at 30% (w/w) lactose was underestimated. The inactivation constant k d was strongly dependent on temperature in buffer, whereas only a slight increase in k d was found with temperature at high substrate concentrations. The enzyme stability was found to increase strongly with the initial substrate concentrations. The inactivation energy E a appeared to be lower at high initial substrate concentrations.
authors.affiliation: Food Process Engineering Group, Wageningen University, PO Box 8129, Wageningen, EV 6700 The Netherlands.
authors.forename: Anja
authors.initials: A
authors.lastname: Warmerdam
authors.forename: Remko M
authors.initials: RM
authors.lastname: Boom
authors.forename: Anja Em
authors.initials: AE
authors.lastname: Janssen
keywords: Bacillus circulans; Concentrated systems; Enzyme activity; Enzyme stability; Galacto-oligosaccharides; β-galactosidase
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