Differential fermentation of glucose-based carbohydrates in vitro by human faecal bacteria--a study of pyrodextrinised starches from different sources.
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 water-soluble and has non-starch linkages. However, a full characterisation of the fermentation properties of pyrodextrins has not been reported.


OBJECTIVE
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 degrees 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.
Laurentin
Alexander
A
Gut Food and Metabolism Section, Division of Developmental Medicine, University of Glasgow, Yorkhill NHS Trust, Glasgow, G3 8SJ, Scotland, UK.
Edwards
Christine A
CA
D001421:Bacteria, Anaerobic / Q000201:enzymology / Q000378:metabolism*; D002432:Cecum / Q000378:metabolism / Q000382:microbiology; D004063:Digestion; D005232:Fatty Acids, Volatile / Q000032:analysis; D005243:Feces / Q000382:microbiology*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008954:Models, Biological; D012995:Solubility; D013213:Starch
D005232:Fatty Acids, Volatile; D013213:Starch; D005947:Glucose