Differential fermentation of glucose-based carbohydrates in vitro by human faecal bacteria (original) (raw)

Background:

Pyrodextrins, modified starches produced by heat/acid treatment, have been used extensively in the paper industry. Recently, pyrodextrinisation has been recognised as a way of producing a “resistant starch” that is watersoluble and has non-starch link-ages. However, a full characterisation of the fermentation properties of pyrodextrins has not been reported.

Aim of the study:

To evaluate the effect of pyrodextrinisation on the fermentation characteristics of starches, prepared from Venezuelan crops, in a simple in vitro model of the human colon.

Methods:

Potato, lentil and cocoyam pyrodextrins were produced using heat (140°C for 3 h) and hydrochloric acid as catalyst (1.82 g/kg starch). Then, both native and modified starches were pre-digested with pepsin and pancreatic enzymes and their resistant components fermented anaerobically using human faeces as inocula for 24 h. Short-chain fatty acids (SCFA), pH, residual starch and carbohydrate in the cultures were measured.

Results:

More than 69% of initial carbohydrate disappeared from both pre-digested native and pyroconverted starch cultures. More than 6.8 and 10.0 mmol net SCFA per gram carbohydrate were produced from pre-digested native and pyrodextrinised starches, respectively. In cultures of predigested pyrodextrins, the molar ratio for propionate doubled, whereas the ratio of acetate decreased by 25% when compared with pre-digested native starches. The ratio of butyrate did not change.

Conclusions:

The mechanism for the change in SCFA profile is unclear, but may be related to solubility and/or presence of nonstarch linkages. The presence of these bonds may modify the accessibility/affinity of bacterial enzymes to the modified starch structure.