Unfermented gel fraction from psyllium seed husks

Details Unfermented gel fraction from psyllium seed husks Unfermented gel fraction from psyllium seed husks

2001-09-10

2004-01-13

Prats, Francisco (Department: 1651)

Drug, bio-affecting and body treating compositions

Plant material or plant extract of undetermined constitution...

Containing or obtained from plantago

C424S725000, C536S123000, C536S128000, C514S054000

Reexamination Certificate

active

06676979

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of laxatives, treatments to lower blood serum cholesterol and low-calorie food thickeners and fat substitutes. In particular, the invention relates to unfermented gel-forming polysaccharides from psyllium seed husks and methods for their isolation.
BACKGROUND OF THE INVENTION
Various scientific and scholarly articles are referred to in parentheses throughout the specification. These articles are incorporated by reference herein to describe the state of the art to which this invention pertains.
The seed husks of psyllium (
Plantago ovata,
also known as ispaghula) are commonly used as a laxative and to promote regular bowel function. Psyllium seed husks promote Taxation partially by increasing the mass and moisture content of the stool (Marteau et al., 1994, Gut 35:1747-1752). Additionally, the excreta of animals and humans fed diets containing psyllium seed husk is gelatinous. This gelatinous property contributes to laxative properties of psyllium seed husks by decreasing friction in the gut. Observed increases in fecal mass and water retention also have been attributed to this gelatinous material (Marteau et al., 1994, supra). The gel is composed largely of unfermented psyllium polysaccharides (Cabotaje et al., 1994, 1302-1307).
Currently used preparations of psyllium seed husks have certain disadvantages. Laxative preparations of psyllium seed husks are generally composed of ground husk and have coarse and unpleasant mouthfeel when administered in drinks. Psyllium seed husks have been incorporated into cookies, crackers and similar products; however, these products have a tendency to begin to gel unpleasantly in the mouth. More significantly, though, psyllium seed husks can swell in the esophagus, producing an esophageal obstruction that can cause choking. For this reason, psyllium seed husk preparations are not recommended for ingestion by persons who may have difficulty swallowing (e.g., elderly persons). Finally, the recommended daily dose of psyllium husk of 3.5-11 g per day is inconvenient to ingest in any form. What is needed is a form of psyllium husk that is convenient and pleasant to use.
Psyllium seed husk has many of the properties of soluble dietary fiber sources. Commonly used sources of soluble dietary fiber include pectin, gums and oat bran. Soluble dietary fiber (SDF) has many uses in food and medicinal preparations. Soluble fibers are components of minimally processed food sources such as oats, oat bran and barley, or are available as concentrates, such as gums, pectins and mucilages. Gums and mucilages are carbohydrate polymers that are generally isolated from plant sources. Mucilages in particular produce slippery or gelatinous solutions in water. Pectins are polymeric chains of partially methylated galacturonic acids that also possess the ability to form a gel in water. Most soluble fibers are rapidly and completely fermented and have no Taxation properties.
Sources of soluble dietary fiber that are also viscous lower serum cholesterol in animals and humans (Marlett, 1997, pp. 109-121,
Dietary Fiber and Health,
Plenum Press, New York, ed. Kritchevsky and Bonfield). The viscosity of the SDF, rather than its fermentation in the gastrointestinal tract, is key to its hypocholesterolemic action (Marlett et al., 1994, Hepatology 20:1450-1457). Viscosity in the lumen of the lower small intestine interferes with the absorption of bile acids and more bile acids are lost through the stool. Blood cholesterol is thought to be lowered primarily because it is being used in the liver to synthesize more bile acids to replace those lost. The synthesis of bile acids in the liver accounts for 40 to 50% of the daily elimination of cholesterol from the blood. However, the addition of one source of soluble fiber, oat bran, to the diet also increases the proportion of deoxycholic acid in the bile acid pool, which decreases the absorption of exogenous dietary cholesterol. Supplementing the diet with psyllium husk also increases the excretion of bile acids by about 50% (Gelissen et al., 1994, Am. J. Clin. Nutr. 59:395-400).
Soluble dietary fiber concentrates are also often used as thickeners and low calorie fat substitutes in the food industry because of their hydrocolloidal properties (Ward, 1997, Cereal Foods World, 42:386-390). Low-viscosity gums such as gum acacia have both hydrophilic and lipophilic properties that make them ideal as emulsifiers, surfactants and stabilizers. Pectins and mucilages have gel-forming properties that made them ideal thickeners of food products. Pectins are traditionally extracted from apple and citrus fruits. Commonly used mucilages are generally extracted from seaweed and include carrageenan, agar and alginate. A fat substitute can be made by combining gum with mucilage and/or pectin to create a compound with the emulsifying properties and smoothness of a fat.
SUMMARY OF THE INVENTION
The present invention provides the gel-forming component of psyllium seed husks in a purified form. This gel fraction provides the Taxation and hypocholesterolemic effects of intact psyllium seed husks, but is in a form that is easily administrable as a tablet, capsule or liquid, without certain unpleasant or unsafe qualities associated with the use of intact psyllium seed husks. The gel fraction also has utility in treatment of other intestinal abnormalities and maintaining normal bowel function, and as a food thickener and fat replacement.
According to one aspect of the invention, a gel-forming fraction of psyllium seed husks that survives microbial fermentation upon passage through a monogastric mammalian digestive tract is provided. Among other components, the gel fraction comprises predominantly xylose and arabinose in a dry weight ratio of at least about (preferably about 3.5). The fraction comprises notably limited amounts of other sugars, e.g., about 2.5%-13.5% total of rhamnose, galactose, glucose and uronic acids. More specifically, the gel-forming fraction has the following sugar composition, expressed as a percentage of total sugars:
between about 0.5% and 4% rhamnose;
between about 19% and 22% arabinose;
between about 68% and 76% xylose;
between about 0% and 0.5% mannose;
between about 1% and 2% galactose
between about 0% and 1% glucose; and
between about 1% and 6% uronic acids
Upon further purification, the gel-forming fraction becomes even more depleted in rhamnose, glucose and uronic acids.
The gel-forming fraction is also highly viscous, a 0.2% concentration in formamide having an apparent viscosity of at least 500 sec, preferably 750 sec, and most preferably 850 sec. The fraction is soluble in a dilute alkaline solution and forms a gel upon acidification of the solution to a final pH of about 4.5.
According to another aspect of the invention, in a preferred method of obtaining the psyllium seed husk gel-forming fraction, a separate carbohydrate fraction is also obtained. This fraction is soluble in the dilute alkaline solution and remains soluble upon acidification of the solution to a pH of about 4.5. This fraction is comprised of xylose and arabinose in a ratio of at least about 4:1 and further comprises at least about 12% (by weight) rhamnose and at least about 15% (by weight) uronic acids.
According to another aspect of the invention, a method of fractionating psyllium seed husks to obtain a gel-forming fraction and an additional carbohydrate fraction is provided. The method comprises: (a) mixing the husks, in the presence of a chemical reducing agent, in an aqueous alkaline solution comprising between about 0.15 and about 1.0 M (preferably 0.15-0.5 M, more preferably 0.15-0.4 M, even more preferably 0.15-0.3 M and most preferably 0.15-0.2 M) hydroxyl ions, thereby fractionating the husks into an alkali soluble fraction and an alkali-insoluble fraction; (b) removing the alkali insoluble fraction; (c) acidifying the alkali soluble fraction to a pH of between about 3 and about 6 (preferably between about 4 and about 5, most preferably about 4.5), which results in the gelation of the g

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