ten. The β-(2,1) linkage is resistant to enzymatic digestion. Synthetic oligofructose contains β-(2,1) fructose chains with and without terminal glucose units. The chain ranges from two to eight monosaccharide residues. Synthetic fructooligosaccharides have the same chemical and structural composition as oligofructose, except that the degree of polymerization ranges from two to four. Because many current definitions of dietary fiber are based on methods involving ethanol precipitation, oligosaccharides and fructans that are endogenous in foods, but soluble in ethanol, are not analyzed as dietary fiber. Thus, the USDA database does not currently include these fiber sources. With respect to the definitions outlined in this chapter, the naturally occurring fructans that are found in plants, such as chicory, onions, and Jerusalem artichoke, would be classified as Dietary Fibers; the synthesized or extracted fructans could be classified as Functional Fibers when there are sufficient data to show positive physiological effects in humans.

Lignin. Lignin is a highly branched polymer comprised of phenyl-propanoid units and is found within “woody” plant cell walls, covalently bound to fibrous polysaccharides (Dietary Fibers). Although not a carbohydrate, because of its association with Dietary Fiber, and because it affects the physiological effects of Dietary Fiber, lignin is classified as a Dietary Fiber if it is relatively intact in the plant. Lignin isolated and added to foods could be classified as Functional Fiber given sufficient data on positive physiological effects in humans.

Pectins. Pectins, which are found in the cell wall and intracellular tissues of many fruits and berries, consist of galacturonic acid units with rhamnose interspersed in a linear chain. Pectins frequently have side chains of neutral sugars, and the galactose units may be esterified with a methyl group, a feature that allows for its viscosity. While fruits and vegetables contain 5 to 10 percent naturally occurring pectin, pectins are industrially extracted from citrus peels and apple pomace. Isolated, high methoxylated pectins are mainly added to jams due to their gelling properties with high amounts of sugar. Low methoxylated pectins are added to low-calorie gelled products, such as sugar-free jams and yogurts. Thus, pectins in the diet are classified as Dietary and/or Functional Fiber.

Polydextrose. Polydextrose is a polysaccharide that is synthesized by random polymerization of glucose and sorbitol. Polydextrose serves as a bulking agent in foods and sometimes as a sugar substitute. Polydextrose is not digested or absorbed in the small intestine and is partially fermented in the large intestine, with the remaining excreted in the feces. Polydextrose