Continuous Packed Bed Reactor With Immobilized Beta-Galactosidase For Production Of Galactooligosaccharides (Gos)

The beta-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-beta-d-galactopyranoside (ONPG). The biocatalyst showed excellent operational stability in 14 successive 20 min reaction cycles at 45 degrees C in a batch reactor. A continuous process for GOS synthesis was operated for 213 h at 0.2 mL/min and 45 degrees 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-beta(1 -> 4)-Gal-beta(1 -> 4)-Gal-beta(1 -> 4)-Glc and the tetrasaccharide Gal-beta(1 -> 4)-Gal-beta(1 -> 4)-Gal-beta(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 beta-galactosidases.