S Skeie

Publications (2)2.56 Total impact

• Article: Survival of lactic acid bacteria from fermented milks in an in vitro digestion model exploiting sequential incubation in human gastric and duodenum juice.

  T Faye, A Tamburello, G E Vegarud, S Skeie
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  ABSTRACT: In the present study, the survival of 9 lactic acid bacteria (5 Lactococcus strains, 3 Lactobacillus strains, and 1 strain of Enterococcus hirae), was investigated in vitro under conditions similar to human digestion using human gastric and duodenal juices. The tolerance of the bacteria was also tested with traditional methods using acidic conditions and bile salts. The strains were subjected to a model digestive system comprising sequential incubation in human gastric and duodenal juices, in a 2-step digestion assay at 37°C, simulating the human upper gastrointestinal tract with human gastric juices at pH 2.5 and human duodenal juices at pH 7. The bacterial strains were tested either as washed cells from culture media or in fermented milk. The initial in vitro testing in acid and bile salts showed that Lactobacillus strains and the E. hirae strain displayed a significantly higher acid tolerance than the lactococci. The lactobacilli and the Enterococcus numbers increased, whereas the lactococci decreased at least 1 log during the bile salt treatment. The Lactobacillus strains showed the highest survival rate in the model digestive system when washed bacterial cultures were used with a minor log reduction, whereas the lactococci numbers were reduced by at least log 4. However, when using fermented milks in the model digestion system it was demonstrated that the Enterococcus strain and 2 strains of Lactococcus lactis ssp. cremoris benefited significantly from the presence of the fermented milk as food matrix, with log numbers >log 7 and 5, respectively, after digestion of the fermented milk. The analyses reported comprise a comprehensive in vitro testing regimen suitable for evaluation of the survival of candidate probiotic bacteria in human digestion as an initial prescreen to clinical trials.
  Journal of Dairy Science 02/2012; 95(2):558-66. · 2.56 Impact Factor
• Article: Seasonal and regional variation in the composition of whey from Norwegian Cheddar-type and Dutch-type cheeses

  A.G. Johansen, G.E. Vegarud, S. Skeie
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  ABSTRACT: The compositional variation in Norwegian whey from two cheese sources (Dutch and Cheddar-type cheeses) was analysed according to the type of cheese, geographical region and season of production. Whey composition found to differ between season and type of cheese in production, with the seasonal variation in the protein composition most clearly expressed in Cheddar-type cheese whey. The lowest protein concentrations were measured during spring season, and the maximum during summer season. The content of fat and urea was also significantly different at various times of the year. The geographical differences in whey composition and its interaction with season were investigated for Dutch-type cheese whey. The northern region of Norway showed a significantly different composition of the whey compared to the other investigated regions. The differences were expressed in higher content of total solids and fat, and different mineral compositions. The composition of Norwegian whey differed from cheese whey sources in other countries, particularly in terms of protein content and pH.
  International Dairy Journal.