Bifidogenic effects of Cordyceps sinensis fungal exopolysaccharide and konjac glucomannan after ultrasound and acid degradation

The bifidogenic effects of exopolysaccharide (EPS) of a medicinal fungus ( Cordyceps sinensis ) and a well-known food polysaccharide konjac glucomannan (KGM) with different molecular weight (MW) ranges were evaluated through in vitro experiments in liquid cultures of Bifidobacteria . Native EPS and KGM were partially degraded with power ultrasound (US) to improve the water solubility, and further hydrolysed with trifluoroacetic acid to much lower MW. The acid-hydrolysed fractions (EPS-AH and KGM-AH) supported the growth of all five tested bifidobacterial species, while the US-degraded high MW fractions, EPS-US and KGM-US, could only slightly support the growth of some species. All EPS fractions increased the acetic acid production of most bifidobacterial species. Most remarkably, the high MW EPS-US, EPS-AH and KGM-US fractions significantly enhanced the cell viability with much higher colony forming unit (CFU) counts, suggesting a protective effect of these high MW polysaccharides for the bacterial survival . The results have shown that MW was a significant factor on the bifidogenic properties of partially degraded EPS and KGM.