The study – published in the Journal of Dairy Science – describes the development of a ‘model gastric system’ for evaluating the survival of bacteria strains in the human digestive system. Using the model, the researchers from the Norwegian University of Life Sciences, determined that some bacteria strains survive better when consumed as fermented milks.
The researchers said the model digestion experiments allowed them to simulate with more precision the multiple stress factors that might ultimately affect the survival and subsequent performance of bacteria in the gut.
"Most of the bacterial strains we tested have interesting functional properties related to food products. We wanted to evaluate whether these strains could contribute with beneficial health functions, or even have the potential as probiotics for human consumption," explained lead investigator Professor Siv Skeie.
"These results seem to confirm that foods, such as fermented milks, could be a protective matrix enhancing survival of some bacteria," he said.
In the research, Skeie and his team assessed the survival of nine lactic acid bacteria (five Lactococcus strains, three Lactobacillus strains, and one strain of Enterococcus hirae), in vitro under conditions similar to human digestion – using human gastric and duodenal juices.
The bacterial strains were tested either as washed cells from culture media or in fermented milk.
Skeie and colleagues revealed that initial in vitro testing in acid and bile salts showed that Lactobacillus and E. hirae strains “displayed a significantly higher acid tolerance than the Lactococci.”
However, in the model digestive system, the Lactobacilli strains showed the highest survival rate.
Skeie and collegues also noted that while none of the Lactococcal and E. hirae stains survived in significant numbers after exposure to the gastric juices, their numbers increased in the subsequent duodenal phase.
"This could mean that Lactococci and Enterococci are able to resurrect their viability if they are exposed to more suitable conditions like those in the small intestine. This is very interesting because it is in the intestine that functional or probiotic bacteria confer their health benefit to the host," suggested Skeie.
In particular, they reported that fermented milk improved the viability of the Lactococcus strains Ar-1, Bf-2, and E. hirae INF E1 during incubation under gastric conditions, said the researchers.
Source: Journal of Dairy Science
Volume 95, Issue 2 , Pages 558-566, doi: 10:3168/jds.2011-4705
“Survival of lactic acid bacteria from fermented milks in an in vitro digestion model exploiting sequential incubation in human gastric and duodenum juice”
Authors: T. Faye, A. Tamburello, G.E. Vegarud, S. Skeie