The findings of the mouse study, to be presented at the International Nutrition and Diagnostic Conference, suggest that fermenting a vegetable common in Japanese cuisine may be linked to an increase in the amount of at least one beneficial bacteria associated with healthy colons.
The vegetable, called burdock root in English and gobo in Japanese, has a minimal positive effect when eaten raw or cooked, said study authors Dr Norihisa Kato, and doctoral student Yongshou Yang, both from Hiroshima University.
They noted that like many high-fiber foods, gobo must be consumed in unrealistically large and unpalatable quantities for it to have any effect on the bacterial composition of the colon. However, previous research in rats suggested that gobo fermented by the fungus Aspergillus was linked to improved colon health.
In the new study, Kato’s research group further investigated this effect – and discovered that the fermentation process produces a solution full of enzymes (known as a protease preparation) and that it is these enzymes that may be responsible for the boost in colon health.
“Rats that ate a diet supplemented with the protease preparation that was derived from gobo fermented by the fungus Aspergillus had amounts of the bacterium Bifidobacterium in their colons that were several hundred times higher than rats on a non-supplemented diet,” said Kato.
“In addition to the microflora improvements, we observed a remarkable improvement of the overall luminal environment of their colons.”
Suggested mechanism
The research team’s untested hypothesis is that the fermented enzyme mixture could be helping to break down undigested proteins into amino acids. This greater availability of amino acids could contribute to improved nutrient utilisation and therefore favourable shifts in gut microbiota composition.
They added that the protease preparation derived from Aspergillus may be a new prebiotic which has a far stronger effects on the Bifidobacterium population in the colon than that of previous varieties of prebiotics, like dietary fibre and oligosaccharides.
Koto and his team also noted that an equivalent amount of the enzyme for an adult person to eat would be approximately 0.1 to 0.4 grams, or 0.04 to 0.16 teaspoons, per day.
Fermented foods
The Japanese cuisine includes many foods fermented with Aspergillus, including the soybean paste miso, the rice wine sake, and various types of pickled vegetables eaten as a side-dish.
However, the results from the Hiroshima University team suggest that regardless of the food, Aspergillus may be responsible for producing a variety of beneficial enzymes, which the team is now beginning to identify and study individually.
“We have completed three years of research on fermented gobo and we’re beginning to understand what component of the fermented product has this beneficial impact on bacteria in the colon,” said Kato.
“We’re excited to do more research to reveal how and why Aspergillus-fermented foods and enzymes, especially acid protease derived from Aspergillus, have positive health effects,” he added.
The team are now planning additional studies on the enzyme’s long-term effects on the colon of rats and the enzyme’s effects on the overall bacterial composition in the intestine of humans.