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Total Dietary Fiber (TDF) in corn flakes samples

Dietary fiber is a mixture of complex organic substances, including hydrophilic compounds such as soluble and insoluble polysaccharides and non-digestibleoligosaccharides as well as a range of nonswellable, more or less hydrophobic compounds such as cutins, suberins and lignins. Dietary fiber is not digested from human stomach and it represents a crucial nutrient in human diet for its ability to enhance satiety, to regulate intestinal functions and to modulate the nutrients absorption. Thanks to its benefits, the fiber is increasingly used in functional foods, and food manufacturers declare the fiber content on the package as part of nutritional labeling.

Total dietary fiber is determined using a combination of enzymatic and gravimetric methods. Duplicate of samples of dried, fat-free foods are gelatinized with heat-stable alpha-amylase and digested using amyloglucosidase to remove starch, and protease to remove proteins. The soluble dietary fiber is precipitated with ethanol. The residue is then filtered, washed with ethanol and acetone, dried and weighed. One of the duplicate samples is assayed for indigested proteins and the other is ashed. The total dietary fiber is the weight of the enzymatic digestion residue less the weight of the undigested protein and ash.

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