Fermentation by gut microbiota cultured in a simulator of the human intestinal microbial ecosystem is improved by supplementing a soy germ powder

By De Boever, P. et al, Ghent, Belgium. J. Nutr 130 (2000): 2599-2606.

Much of the research on health-promoting activities of soy products has been conducted focusing on the role of isoflavones. However, other soy constituents including dietary fiber, oligosaccharides, proteins, trace minerals and vitamins can also influence wellbeing and influence the efficacy of isoflavones.

Study design

As a culture system for gut microflora, a Simulator of the Human Intestinal Microbial Ecosystem (SHIME) was used to evaluate the capacity of SoyLife COMPLEX to modulate colonic fermentation. In addition, it was studied to what extent the microbiota metabolized the conjugated isoflavones present in the soy germ powder into aglycone isoflavones. After stabilization of the gut microbiota in the model system, the bacteria were monitored during 2 weeks. The microbiota were then subjected to a 2-week treatment by adding 2.5 gram per day of SoyLife COMPLEX (1.5% isoflavones as aglycones) to the culture medium.

Results

Addition of SoyLife isoflavone-rich soy germ concentrate resulted in an overall increase of bacterial marker populations, with a significant increase of the Lactobacillus sp. population. However, as is shown in the graph, also bacteria such as enterobacteriaceae, coliforms, Clostridium sp. and Staphylococcus sp. augmented in the study. The explanation of this observation is that the pH of the SHIME-system is controlled throughout the experiments. In vivo however, growth of lactic acid bacteria would lead to a pH-drop, which would prevent the outgrowth of the other named bacteria.

Gas analysis revealed a significant increase of methane concentration. The use of an electronic nose apparatus indicated that odor concentrations after passage through the intestinal tract decreased significantly during the treatment period.

A third observation from this study concerns the estrogenic activity of isoflavones. To enable this activity, glucosides are hydrolysed into aglycones by cleaving the b-glycosidic bonds. This study showed that a change in microflora increased the hydrolysis rate of the isoflavone glucoside, thus resulting in more aglycones. Using a yeast estrogen screen, the estrogenic activity was demonstrated in the crude SHIME-fermented extracts.

In conclusion

This is the first study indicating the ability of soy germ powder to have a positive influence on the composition of the gut microflora. This suggests a prebiotic activity. The estrogenic activity of SoyLife was also confirmed.