Dietary Fiber: Chemistry, Analysis, and Properties

Abstract

This chapter discusses the chemistry analysis and properties of dietary fiber. The consumption of low fiber diets is a common etiological factor in many metabolic and gastrointestinal diseases of the western world. A diet that is rich in foods, which contain plant cell walls is protective against a range of diseases, in particular those prevalent in affluent western communities. Dietary fiber (DF) was initially defined as the skeletal remains of plant cells, in our diet, that are resistant to hydrolysis by the digestive enzymes of man. The principal components of DF are complex polysaccharides, some of which are associated with polyphenolics and proteins. The parenchymatous tissues are particularly important in connection with DF, because the walls of these tissues comprise the bulk of the DF from fruits, vegetables, the cotyledons of seeds, and the endosperm of cereals. The cell walls of parenchymatous tissues contain approximately 3–6% of the dry weight of the walls as proteins. From the carbohydrate compositions of the starch-free alcohol-insoluble residues of guar seeds and dehusked guar seeds, it can be inferred that galactomannans are the major cell wall polysaccharides of the dehusked seeds. The water-holding capacity of fiber from bran is low compared with those of vegetable preparations. Cell walls of lignified tissues of dicotyledons contain relatively small amounts of pectin, and as the middle lamella region is impregnated with lignin, it is difficult to get an estimate of the titratable carboxyl groups of the fiber after exposure to acid.