Prebiotic effects of structurally identified galacto-oligosaccharides produced by β-galactosidase from Aspergillus oryzae

Novel galacto-oligosaccharides were produced by β-galactosidase from Aspergillus oryzae using lactose, and their structural characteristics and prebiotic effects were examined. Highly purified oligosaccharide fraction (HP) was prepared from a crude one (low purified, LP) by gel-filtration on Biogel P-2 column, which was further purified into S1 and S2 fractions by prep-HPLC. S1 and S2 were comprised of galactose (Gal) and glucose (Glc) in the ratio of 2 to 1. ESI-MS-MS and methylation analysis indicated that S1 and S2 were trisaccharides with structures of β- d -Gal p -(1,6)-β- d -Gal p -(1,4)-β- d -Glc p and β- d -Gal p -(1,3)-β- d -Gal p -(1,4)-β- d -Glc p , respectively. Herein, LP and HP were used as the carbon sources for determining the prebiotic activity score of probiotics including Lactobacillus and Bifidobacterium species. LP and HP at 1% and 2% (w/v) were observed at all positive scores on several probiotics, especially, B. infantis ATCC 15697 at the 2% level of HP ( p