期刊
JOURNAL OF DAIRY SCIENCE
卷 97, 期 2, 页码 694-703出版社
ELSEVIER SCIENCE INC
DOI: 10.3168/jds.2013-7492
关键词
galactooligosaccharide; prebiotics; Sulfolobus; extremophile
资金
- Midwest Dairy Association (St. Paul, MN)
Galactooligosaccharides (GOS) are novel prebiotic food ingredients that can be produced from lactose using P-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 beta-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 degrees C. A maximum production of 197 g/L of COS 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.
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