The active fraction of psyllium seed husk.
A series of experiments and evaluations of fractions isolated from psyllium seed husk (PSH) were used to test the overall hypothesis that a gel-forming component of PSH is not fermented and that it is this component that is responsible for the laxative and cholesterol-lowering properties of PSH. A gel is isolated from human stools collected during a controlled diet study when PSH is consumed but not when the control diet only is consumed. Evaluations of three fractions isolated from PSH suggest that gel-forming fraction B, which is about 55% of PSH, is poorly fermented and is the component that increases stool moisture and faecal bile acid excretion, the latter leading to lower blood cholesterol levels. Fraction C, representing < 15% of PSH, is viscous, but is rapidly fermented. Fraction A is alkali-insoluble material that is not fermented. In concentrations comparable with their presence in PSH, fractions A and C do not alter moisture and bile acid output. The active fraction of PSH is a highly-branched arabinoxylan consisting of a xylose backbone and arabinose- and xylose-containing side chains. In contrast to arabinoxylans in cereal grains that are extensively fermented, PSH possesses a structural feature, as yet unidentified, that hinders its fermentation by typical colonic microflora.
Department of Nutrition Sciences, University of Wisconsin-Madison, Wisconsin 53706, USA. jmarlett@nutrisci.wisc.edu
Judith A
JA
Marlett
Milton H
MH
Fischer
D002400:Cathartics / Q000008:administration & dosage / Q000494:pharmacology*; D003106:Colon / Q000382:microbiology; D004043:Dietary Fiber / Q000008:administration & dosage / Q000494:pharmacology*; D005243:Feces / Q000737:chemistry; D005285:Fermentation; D005782:Gels; D006801:Humans; D006937:Hypercholesterolemia / Q000188:drug therapy*; D011620:Psyllium / Q000737:chemistry*; D014783:Viscosity
D002400:Cathartics; D004043:Dietary Fiber; D005782:Gels; D011620:Psyllium