Enzymic hydrolysis, dietary fiber

Metabolism of pectin. Pectin has only recently come, to be considered a part of the dietary fiber complex. Previously it was excluded because 1) it is not fibrous (except at the molecular level), 2) it escapes detection in standard fiber tests owing to its solubility, and 3) it usually does not survive intestinal passage. In a reassessment of which dietary components should be considered fiber, Trowell (49) proposed that dietary fiber include those constituents of food resistant to hydrolysis by man s alimentary enzymes. Spiller (50, 51) suggested that confusion surrounding the term "fiber" be avoided by using the term "plantix" to denote those plant materials of polymeric nature not attacked by human digestive enzymes. 

The degradation of plant cell walls requires fra/is-p-coumaroyl esterase, an important enzyme in the digestion of forages and dietary fiber. The trans-p-coumaric acid released by enzymatic hydrolysis was assayed by reversed-phase HPLC. 

A major complication of constipation in the elderly is fecal impaction, a potentially serious condition that can result from ignoring impulses to defecate. Impaction is the buildup of fecal mass that becomes too large to expel. Increasing dietary fiber is part of the management program for chronic constipation of the elderly. Addition of bran (6-20 g/day) increases fecal weight and increases the frequency of defecation. When wheat bran is not effective, the laxative lactulose is recommended. Lactulose is a disaccharide composed of galactose and fructose connected by a p(l 4) bond. This compound is absorbed poorly in the small intestine because of the absence of enzymes that catalyze its hydrolysis. 

Analysis of dietary fiber. Total dietary fiber including both water-soluble and water-insoluble components was analysed with an enzymic method as described by Asp et al. (18). The dietary fiber was characterized by gas-liquid chromatographic assay of monosaccharides after acid-hydrolysis and gravimetric determination of acid insoluble lignin. Uronic acids were assayed with a decarboxylation method. These analyses were performed as described by Theander and Aman (19). 

The widely accepted definition of dietary fiber as proposed by Trowell (1) refers to "plant polysaccharides and lignin which are resistant to hydrolysis by digestive enzymes of man" as the sole constituents of dietary fiber. Being limited to the plant polymers only, this definition does not include undigestible polysaccharides from other sources such... 

Dietary fibers represent a gronp of carbohydrates, isolable from different plant sources, that are resistant to hydrolysis by enzymes of the gastrointestinal tract. They are divided into two groups water soluble fibers, among which the main are the p-glncans and arabinoxylans, and water insoluble fibers, which include lignins, celluloses, and hemicelluloses. 

This paper used a combinatorial method of enzyme and chemical method to extract dietary fiber from Sargassum fusiforme. The optimal combination were mass ratio of trypsin and cellulose as 30 1, hydrolysis temperature as 40°C and hydrolysis time as 1.5 h, 2.5% NaOH with 30 volume, NaOH extraction temperature as 65°C and extraction time as 2h.The yield of dietary fiber could reach 23%. The product was light yellow and could be a supplement source of dietary fiber. This study provided a new process for the comprehensive utilization of Sargassum fusiforme. 

Dietary fiber has been defined as the skeletal remains of plant cells, that are resistant to hydrolysis by the enzymes of men. The possible role of these unavailable carbohydrates as cellulose, lig-nine, pentosans, uronic acids and of pectines against hyperlipemia and ischemic heart disease has been noticed in the low blood cholesterol levels of vegetarian people and of populations consuming natural starchy carbohydrates. 

Taherzadeh, M.J., Karimi, K., 2007. Enzymatic-based hydrolysis processes for ethanol. BioResources 2 (4), 707-738. Tasse, L., Bercovici, J., Pizzut-Serin, S., Robe, R, Tap, J., Klopp, C., Cantarel, B.L., et al., 2010. Fvmctional metagenomics to mine the human gut microbiome for dietary fiber catabolic enzymes. Genome Research 20 (11), 1605-1612. Van Berkel, R., 2000. Cleaner Rroduction for Rrocess Industries. Plenary Lecture. Chemeca, Perth WA. 

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