title: Galacto-oligosaccharides synthesis from lactose and whey by β-galactosidase immobilized in PVA.
abstract: The synthesis of galacto-oligosaccharides (GOS) by β-galactosidase immobilized in both polyvinyl alcohol (PVA) lenses and sol-gel carriers was studied and compared with the performance of the free enzyme. PVA-immobilized β-galactosidase retained 95 % of the initial activity after seven repeated uses and retained 51 % of the initial activity after 3 months of storage, while sol-gel-immobilized β-galactosidase only retained 39 % of the initial activity under storage. Lactose conversion takes place at a higher rate in the PVA-immobilized β-galactosidase, while the lowest rate of lactose conversion was noticed with immobilized β-galactosidase in sol-gel. Continuous production of GOS from either lactose or whey, with PVA-immobilized β-galactosidase, was performed in a packed-bed reactor. A maximum GOS production of 30 % of total sugars was attained for a 40-% lactose feed solution with a feed rate of 10.8 ml/h, at pH 4.5 and 40 °C, corresponding to a productivity of 117 g/l h. The maximum GOS productivity of 344 g/l h was obtained at a flow rate of 28.7 ml/h. 3-OS and 4-OS were the major types of GOS formed. Conversion of whey in continuous mode resulted in GOS production of 15 % of total sugars and formation of 45 % 3-OS, 40 % 4-OS, and 15 % 5-OS.
authors.affiliation: IBB-Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Universidade Técnica de Lisboa, Av. Rovisco Pais, Lisbon, Portugal.
authors.forename: Ruzica
authors.initials: R
authors.lastname: Jovanovic-Malinovska
authors.forename: Pedro
authors.initials: P
authors.lastname: Fernandes
authors.forename: Eleonora
authors.initials: E
authors.lastname: Winkelhausen
authors.forename: Luis
authors.initials: L
authors.lastname: Fonseca
mesh_terms: D019149:Bioreactors; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism; D005690:Galactose / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007785:Lactose / Q000737:chemistry; D008894:Milk Proteins / Q000737:chemistry; D009844:Oligosaccharides / Q000138:chemical synthesis* / Q000737:chemistry; D011142:Polyvinyl Alcohol / Q000737:chemistry; D013379:Substrate Specificity; D000067816:Whey Proteins; D001616:beta-Galactosidase / Q000737:chemistry / Q000378:metabolism
chemical_list: D004800:Enzymes, Immobilized; D008894:Milk Proteins; D009844:Oligosaccharides; D000067816:Whey Proteins; D011142:Polyvinyl Alcohol; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose