A pseudo steady‐state model for galacto‐oligosaccharides synthesis with β‐galactosidase from Aspergillus oryzae

Abstract

A pseudo steady-state model for the kinetically controlled synthesis of galacto-oligosaccharides (GOS) with Aspergillus oryzae β-galactosidase is presented. The model accounts for the dynamics of lactose consumption and production of galactose, glucose, di, tri, tetra, and penta-oligosaccharides during the synthesis, being able to describe the total GOS content in the reaction medium at the experimental conditions evaluated. Experimental results show that the formation of GOS containing only galactose residues is significant at high conversions of substrate, which was taken into account in the model. The formation of enzyme transition complexes was considered and reasonable assumptions were made to reduce the number of parameters to be determined. The model developed has 8 parameters; 2 of them were experimentally determined and the other 6 were estimated by fitting to the experimental data using multiresponse regression. Temperature effect on kinetic and affinity constants was determined in the range from 40 to 55°C, and the data were fitted to Arrhenius type equation. Parameters of the proposed model are independent from the enzyme load in the reaction medium and, differently from previously reported models, they have a clear biochemical meaning. The magnitude of the kinetic and affinity constants of the enzyme suggests that the liberation of galactose from the galactosyl-enzyme complex is a very slow reaction and such complex is driven into GOS formation. It also suggests that the affinity for sugars of the galactosyl-enzyme complex is higher than that of the free enzyme.

Improvement of thermal stability of β-galactosidase from Bacillus circulans by multipoint covalent immobilization in hierarchical macro-mesoporous silica

“…Recent researches in GOS synthesis with ␤-gal have shown that temperature increase generates a significant increase in GOS conversion [5,6], thereby it is necessary to obtain new active heterogeneous biocatalysts exhibiting high thermal stability and able to be reused. These objectives can be achieved by enzyme immobilization on solid supports, which also allows the development of continuous and sequential batch processes [7].…”

Whey upgrading by enzyme biocatalysis

“…Variants of this model have been proposed aiming to a better description of the reaction system (Kim et al 2004;Neri et al 2009a) but they contain too many kinetic parameters that are difficult to estimate. We have constructed a simplified model that accounts for the synthesis of GOS-2, GOS-3, GOS-4 and GOS-5 containing a reduced number of kinetic parameters that can be determined by non-linear multiresponse fitting to experimental data (Vera et al 2011a). …”

“…GOS are oligosaccharides composed by a variable number of galactose units (from one to ten, usually from two to four) and a terminal glucose unit, linked mostly by β1-4 and β1-6 bonds (Casci and Rastall, 2006), even though some polygalactose oligosaccharides not containing glucose can also be formed at low levels during synthesis (Sanz et al 2002;Vera et al 2011a). Disaccharides (mostly galactoseglucose) are refereed as GOS-2, trisaccharides (mostly galactose-galactose-glucose) as GOS-3, tetrasaccharides (mostly galactose-galactose-galactose-glucose) as GOS-4 and so on.…”

Potential Applications of Carbohydrases Immobilization in the Food Industry

“…Several models have been proposed to describe oligosaccharide synthesis and simultaneous lactose hydrolysis, ultimately pointing for the need of a high initial lactose concentration, viz. 40% w / v and above [6,119–122]. The recent findings of Vera and co-workers established that an increase in the initial lactose concentration only influences positively the maximum product yield, provided the lactose remains dissolved [6].…”