In vitro fermentation of dietary fiber by human fecal organisms

Microbial in vitro methods were used to evaluate 20 different sources of dietary fiber. Bacteria collected from human fecal matter were grown in continuous culture, bath culture and agar plates. Bacteria grown on pectin or Solka floc® (SW40) in continuous culture flasks were incubated in batch cultures. Experiments using human fecal bacteria, batch culture flasks and 16 sources of dietary fiber were conducted in order to study: (1) the water-holding capacity of the dietary fiber and the residues from fermentation; (2) the rates of gas release (measured 12 times over 24 h). The wide range in the water-holding capacity of the original substrates was greatly reduced after fermentation and was normalized to about 3.5 g water g^-1 of residual organic matter (OM). Estimated gas release per 24 h g^-1 of OM fermented ranged from 543 ml for pectin to 370 ml for psyllium. Composition of the gas released in continuous culture flasks fed pectin was manipulated by the presence or lack of wheat straw. This wheat straw was used as an inert, insoluble dietary fiber source. Long-term depression in the capacity of the inocula to ferment pectin was induced by feeding Solka floc® to a person or to bacteria grown in continuous culture flasks.