Abstract
The β-galactosidase from Bacillus circulans was covalently attached to aldehyde-activated (glyoxal) agarose beads and assayed for the continuous production of galactooligosaccharides (GOS) in a packed-bed reactor (PBR). The immobilization was fast (1 h) and the activity of the resulting biocatalyst was 97.4 U/g measured with o-nitrophenyl-β-d-galactopyranoside (ONPG). The biocatalyst showed excellent operational stability in 14 successive 20 min reaction cycles at 45 °C in a batch reactor. A continuous process for GOS synthesis was operated for 213 h at 0.2 mL/min and 45 °C using 100 g/L of lactose as a feed solution. The efficiency of the PBR slightly decreased with time; however, the maximum GOS concentration (24.2 g/L) was obtained after 48 h of operation, which corresponded to 48.6% lactose conversion and thus to maximum transgalactosylation activity. HPAEC-PAD analysis showed that the two major GOS were the trisaccharide Gal-β(1→4)-Gal-β(1→4)-Glc and the tetrasaccharide Gal-β(1→4)-Gal-β(1→4)-Gal-β(1→4)-Glc. The PBR was also assessed in the production of GOS from milk as a feed solution. The stability of the bioreactor was satisfactory during the first 8 h of operation; after that, a decrease in the flow rate was observed, probably due to partial clogging of the column. This work represents a step forward in the continuous production of GOS employing fixed-bed reactors with immobilized β-galactosidases.
Highlights
In addition to the hydrolysis of lactose, β-galactosidases (β-D-galactoside galactohydrolases, EC 3.2.1.23) catalyze transgalactosylation reactions in which lactose—or the released glucose and galactose—act as galactosyl acceptors, yielding a series of condensation products called galactooligosaccharides (GOS) [1,2]
The packed-bed reactors (PBR) was assessed in the production of GOS from milk as a feed solution
GOS constitute a group of prebiotics that modulate the colonic microbiota, providing health benefits such as an improvement in mineral absorption and the prevention of colon cancer [5,6]
Summary
In addition to the hydrolysis of lactose, β-galactosidases (β-D-galactoside galactohydrolases, EC 3.2.1.23) catalyze transgalactosylation reactions in which lactose—or the released glucose and galactose—act as galactosyl acceptors, yielding a series of condensation products called galactooligosaccharides (GOS) [1,2]. Covalent immobilization has the advantage of forming robust linkages between product recovery easier—and enhancement of enzyme resistance against inactivation by different the enzyme and the carrier, which minimizes the loss of activity caused by enzyme leakage from the denaturants [8,9]. Covalent immobilization has the advantage of forming robust linkages between support [10], extends its lifetime by protecting the three-dimensional structure of the protein [11] and the enzyme and the carrier, which minimizes the loss of activity caused by enzyme leakage from the allows the development of continuous processes. Compared with other β-galactosidases, this enzyme givesa rise to presence a notableofGOS yield It isto appropriate for the dairy bonds [18].
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