Classifications

Various food components have been recognized to have prebiotic activity, including various fermentable carbohydrates (lactulose, gums, lactilol, soyoligosaccharides, galacto-oligosaccharides Xylo-oligosaccharides. However, the best studied of these have been those classified as dietary fructans. Dietary fructans can either be derived from naturally occurring oligosaccharides or can be artificially synthesized. These carbohydrates contain one or more fructosyl-fructose links that make up the majority of osidic bonds. They are linear or branched fructose (oligo)polymers with either ,3-2-1 linked inulins or ,-2-6 linked levans. These oligo-saccharides exist naturally in many plants including onions, garlic, the roots of Jerusalem artichoke, asparagus root, chicory root, and wheat (Table 1). Inulin is extractable from root plants particularly Jerusalem artichoke and chicory, while fructooligo-saccharide is hydrolyzed from inulin yielding a shorter chain sugar. It is the degree of polymerization (DP) that distinguishes the fructans. Fructo-oligosaccharides are /3-D-fructans with DP between 2 and 10 while inulin has DP 10-60. Essentially, they are sucrose molecules with 1-3 fructose units linked by a /3-(2,1)-glycosidic bond. Most oligo-saccharides are synthesized from sucrose and therefore usually have a terminal glucose end. Inulin, derived from chicory, is broken down using an inulase enzyme making a smaller (2-10) chain with lower DP (4). Oligofructose is a form synthesized from sucrose by /3-fructofuranosidase linking fructose monomers to sucrose.

Both inulin-derived and synthesized fructo-oligosaccharides have been shown to resist digestion in the upper GI tract. Ninety per cent of consumed inulin and fructooligosaccharide was excreted at the terminal ileum of adult ileostomy patients. Furthermore, the undigested oligosaccharides are

Table 1 Fructo-oligosaccharide (FOS) content of common fruits, vegetables, and grains

Food type

FOS concentration (mggm 1)

Fruits

Apples Banana Banana, ripe Blackberry Orange, navel Peach

Raspberry, red Vegetables

Acorn squash Artichoke, globe Artichoke, Jerusalem Chicory root, raw Garlic Onion, red Onion, white Onion powder Peas, snap Peas, snow Shallot

Grains

Barley Oats Rye Wheat Wheat bran Wheat germ

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