Galacto-oligosaccharides (GOS) synthesized from lactose using Aspergillus oryzae beta-galactosidases. We studied the influences of enzyme concentration (0.02-0.1%. w/v), temperature (40-70 degrees C), pH (4.5-8), lactose concentration (5-40%, w/v) and foam architecture reaction media on formation of GOS. The total GOS increased from about 7 to 23 (wt.% of initial lactose) with an increase in lactose from 5 to 40% (w/v). Trisaccharides were the major GOS accounting for approximately 78% (w/w) of GOS. The developed kinetic model for predicting kinetic parameters using the genetic algorithm of MATLAB Software resulted in good agreement between simulated and experimental data. Conducting the reaction in foam architecture with an initial lactose concentration of 20% (w/v), 0.05% (w/v), 0.05% (w/v) enzyme and 0.02% (w/v) ranaspumin-2 (surfactant) at pH of 4.5 and 45 degrees C did not have any effect on reaction and conversion efficiency. The structure of the main fractionated trisaccharide determined with NMR was galactose-beta (1,6)-galactose-beta (1,4)-glucose. (C) 2017 Elsevier Ltd. All rights reserved.