Abstract

The synthesis of galactooligosaccharides (GOS) catalyzed by, beta-galactosidase from Aspergillus oryzae (Enzeco) was studied. Using 400 g/L of lactose and 15 U/mL, maximum GOS yield, measured by HPAEC-PAD, was 26.8% w/w of total carbohydrates, obtained at approximately 70% lactose conversion. No less than 17 carbohydrates were identified; the major transgalactosylation product was 6'-O-beta-galactosyl-lactose, representing nearly one-third (in weight) of total GOS. In contrast with previous reports, the presence of at least five disaccharides was detected, which accounted for 40% of the total GOS at the point of maximum GOS concentration (allolactose and 6-galactobiose were the major products). A. oryzae beta-galactosidase showed a preference to form beta(1 -> 6) bonds, followed by beta(1 -> 3) and beta(1 -> 4) linkages. Results were compared with those obtained with beta-galactosidases from Kluyveromyces lactis and Bacillus circulans. The highest GOS yield and specific productivity were achieved with B. circulans beta-galactosidase. The specificity of the linkages formed and distribution of di-, tri-, and higher GOS varied significantly among the three beta-galactosidases.