title: Production of galactooligosaccharides using a hyperthermophilic β-galactosidase in permeabilized whole cells of Lactococcus lactis.
abstract: Galactooligosaccharides (GOS) are novel prebiotic food ingredients that can be produced from lactose using β-galactosidase, but the process is more efficient at higher temperatures. To efficiently express the lacS gene from the hyperthermophile Sulfolobus solfataricus, in Lactococcus lactis a synthetic gene (lacSt) with optimized codon usage for Lc. lactis was designed and synthesized. This hyperthermostable β-galactosidase enzyme was successfully overexpressed in Lc. lactis LM0230 using a nisin-controlled gene expression system. Enzyme-containing cells were then killed and permeabilized using 50% ethanol and were used to determine both hydrolysis and transgalactosylation activity. The optimum conditions for GOS synthesis was found to be at pH 6.0 and 85 °C. A maximum production of 197 g/L of GOS tri- and tetrasaccharides was obtained from 40% initial lactose, after 55 h of incubation. The total GOS yield increased with the initial lactose concentration, whereas the highest lactose conversion rate (72%) was achieved from a low lactose solution (5%). Given that a significant proportion of the remaining lactose would be expected to be converted into disaccharide GOS, this should enable the future development of a cost-effective approach for the conversion of whey-based substrates into GOS-enriched food ingredients using this cell-based technology.
authors.affiliation: Department of Food Science and Nutrition, Center for Microbial and Plant Genomics, University of Minnesota, 1500 Gortner Ave., St. Paul 55108.
authors.forename: L
authors.initials: L
authors.lastname: Yu
authors.affiliation: Department of Food Science and Nutrition, Center for Microbial and Plant Genomics, University of Minnesota, 1500 Gortner Ave., St. Paul 55108. Electronic address: dosulliv@umn.edu.
authors.forename: D J
authors.initials: DJ
authors.lastname: O'Sullivan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D015870:Gene Expression; D005813:Genes, Synthetic; D013294:Lactococcus lactis / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D009561:Nisin / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism*; D056692:Prebiotics; D048229:Sulfolobus solfataricus / Q000235:genetics* / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D009844:Oligosaccharides; D056692:Prebiotics; D009561:Nisin; D000431:Ethanol; C021499:lactose permease; D001616:beta-Galactosidase
keywords: Sulfolobus; extremophile; galactooligosaccharide; prebiotics