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 o NPG 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 kd was strongly dependent on temperature in buffer, whereas only a slight increase in kd was found with temperature at high substrate concentrations. The enzyme stability was found to increase strongly with the initial substrate concentrations. The inactivation energy Ea appeared to be lower at high initial substrate concentrations.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-402) contains supplementary material, which is available to authorized users.

Highlights

  • For enzymatic production processes it is of interest to use highly concentrated conditions, since energy, water, and material costs can be saved

  • The enzyme activity of β-galactosidases, which is used in the production of galacto-oligosaccharides (GOS), in highly concentrated systems was studied before (Warmerdam et al 2013a) and was found to be strongly influenced by the concentration of reactants and products

  • Conclusions β-Galactosidase from Bacillus circulans was found to be quite stable against temperature at high substrate concentrations

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Summary

Introduction

For enzymatic production processes it is of interest to use highly concentrated conditions, since energy, water, and material costs can be saved. The enzyme activity of β-galactosidases, which is used in the production of galacto-oligosaccharides (GOS), in highly concentrated systems was studied before (Warmerdam et al 2013a) and was found to be strongly influenced by the concentration of reactants and products. The high concentration of reactants and products may lead to more reactions taking place, but it will lead to molecular crowding, which can have large effects on enzyme activity (Minton 2001; Ellis 2001). Their stability can as well be strongly affected by molecular crowding (Minton 2001; Ellis 2001). In 1985, Arakawa and Timasheff (1985) have already described the stabilization of the GOS are usually produced with β-galactosidase at high temperatures and at high substrate concentrations in industry. The inactivation of the enzyme is faster as well (Bruins et al 2003)

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