Galactooligosaccharides formation during enzymatic hydrolysis of lactose: Towards a prebiotic-enriched milk

The formation of galactooligosaccharides (GOS) in skim milk during treatment with several commercial beta-galactosidases (Bacillus circulans, Kluyveromyces lactis and Aspergillus oryzae) was analysed in detail, at 4 and 40 degrees C. The maximum GOS concentration was obtained at a lactose conversion of approximately 40-50% with B. circulans and A. oryzae beta-galactosidases, and at 95% lactose depletion for K. lactis beta-galactosidase. Using an enzyme dosage of 0.1% (v/v), the maximum GOS concentration with K. lactis beta-galactosidase was achieved in 1 and 5 h at 40 and 4 degrees C, respectively. With this enzyme, it was possible to obtain a treated milk with 7.0 g/L GUS - the human milk oligosaccharides (HMOs) concentration is between 5 and 15 g/L - and with a low content of residual lactose (2.1 g/L, compared with 44-46 g/L in the initial milk sample). The major GUS synthesised by this enzyme were 6-galactobiose [Gal-beta(1 -> 6)-Gal], allolactose [Gal-beta(1 -> 6)-Glc] and 6'-0-beta-galactosyl-lactose [Gal-beta(1 -> 4 6)-Gal-beta(1 -> 4)-Glc]. (C) 2013 Elsevier Ltd. All rights reserved.