Paper No.: 01 Paper Title: FOOD CHEMISTRY Module 08: Dietary fibre: Classification, properties and role in health
DIETARY FIBRE CLASSIFICATION, PROPERTIES AND ROLE IN HEALTH T.v.Hymavathi
Introduction Dietary Fiber is an important part of a healthy diet. defined as a food material, particularly plant material, that is not hydrolysed by enzymes secreted by the human digestive tract but that may be digested by microflora in the gut. Plant components that fall within this definition include non-starch polysaccharides (NSP) such as celluloses, some hemi-celluloses, gums and pectins, as well as lignin, resistant dextrins and resistant starches.
Codex Definition ( 2009) Dietary fiber means carbohydrate polymers with ten or more monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans and belong to the categories: Edible carbohydrate polymers naturally occurring in the food as consumed; Carbohydrate polymers, which have been obtained from food raw material by physical, enzymatic, or chemical means and which have been shown to have a physiological effect of benefit to health as demonstrated by generally accepted scientific evidence to competent authorities; Synthetic carbohydrate polymers, which have been shown to have a physiological effect of benefit to health as demonstrated by generally, accepted scientific evidence to competent authorities
Classification of Dietary Fibre Dietary Fiber Soluble Fiber Insoluble Dietary Fiber Dietary Fiber Fermentable Non- Fermentable
Fibre Types and Characteristics, Food Sources and Bacterial Degradation Types of fibre Characteristics Food sources Degradation 1 Soluble Pectins 4% plant polysaccharides, fruits and vegetables Whole wheat flour Gums Legumes, oats, fruits, vegetables, food additives Oatmeal, dried beans Mucilages Synthesized by plant cells Food additives Insoluble Cellulose Structural framework, cereals, Whole wheat flour, Hemicellulose 15 30% cell wall matrix for Bran, cereals, whole + Lignin Mature cell walls Mature vegetables, 0
Major Dietary Fiber Polymers found in Major Food Groups Food Groups Polymers Present Cereals Cellulose,Arabino Xylans,Β D-glucans, Other non cellulosic polysachharides,phenolic Esters, Lignin Vegetables& Fruits Cellulose,Pectic substances,xyloglucans,other non cellulosic polysachharides,lignin Seeds Cellulose,Pectic substances,xyloglucans,other non cellulosic polysachharides,galactomannans Food Additives Gums,Alginates,Sulphated galactans,cellulosic esters and ethers, Modified starches (carboxy methyl cellulose)
PECTINS most widespread soluble dietary fibre chemical name polygalacturonic acids. structural elements of primary cell walls and intercellular regions. isolated from either apple pomace or from citrus peels (levels up to 30% on a dry weight basis) of higher plants. functions as hydrating agent and cementing material of the cellulosic network. one-third of the cell-wall dry substances highest concentration is seen in the middle lamella, with a gradual decrease from the primary cell wall toward the plasma membrane. widely found in fruits, vegetables, legumes, and roots (i.e. sugar beets and potatoes) as storage polysaccharides. The functional groups -free carboxylic acids, methyl esters, or carboxylate anions (as sodium, potassium, or calcium salts). The degree of esterification determines the properties of pectins.
Pectin molecule
Gums Polysaccharide gums are numerous and diverse in nature. harvested from seeds, plant exudates, bacterial cultures, and algae. generally used in very small quantities in foods, and therefore contribute little to total dietary fiber intake. most popular seed gums include guar gum and locust bean gum. Guar gum is harvested from the seeds of Cyamopsis etragonolobus, and locust bean gum comes from Ceratonia siliqua. basic chemical structure, a - β (1 4)-linked D- mannopyranosyl backbone with α-d-galactose side chains linked (1 6) to the mannose backbone. The physical characteristics depends on the degree of the galactosyl branching and pattern of branching basic structure. Plant exudates -gum arabic, gum tragacanth, gum karya, and gum ghatti.
Mucilage They are clear, colorless, gelling agents derived from plants eg. Psyllium. Psyllium is the common to plant genus Plantago used for the production of mucilage. refers to the crude source of dietary fiber, rather than the polysaccharide fraction itself. The gel-forming component of the husk, (55 60% of the dry weight), is a neutral arabinoxylan consisting of a β -(1 4)- linked xylopyranosyl backbone, substituted at position 2 with single xylopyranosyl residues, and at position 3 with a trisaccharide moiety:α-l-arabinofuranosyl-(1 3)-β-Dxylopyranosyl-β(1 3)-β- arabinofuranosyl-(1 3). the major polysaccharide component in psyllium seeds is an acidic glucuronoarabinoxylan, the backbone of which consists of (1 3)-xylopyranosyl linkages interspersed among the normal β -(1 4)-linkages.
Cellulose It is a homopolysaccharide consisting of β -(1 4)-linked glucose residues. β- (1 4) linkage allows cellulose polymers to arrange into rigid, insoluble microfibrils through multiple hydrogen bonds. microfibrils provide structural integrity and mechanical support for plants found in whole grains, fruits, and vegetables. It can be obtained commercially from wood pulp and added to food as an anti caking, thickening, or texturizing agent uses in food are limited due to gritty texture and demonstrates little functionality in food. chemical modification and high shear accompanied by alkaline and hydrogen peroxide treatments improves functionality. modifications can result in water- or oil-soluble polymers that can be used in food or drug delivery applications. the maximum degree of substitution that modified cellulose can have is three.
Hemicelluloses It is a polysaccharide substance extractable from agricultural biomass with aqueous alkali solutions. made up of a variety of pentoses and hexoses, including arabinose, fructose, galactose, glucose, mannose, and uronic acids. Two types : xylans and galactans. β -Glucans and mannans sometimes grouped under hemicelluloses. Xylans can be found in hardwoods, herbaceous plants, and grasses, but the most important food sources of xylans are cereals. Cereal xylans are referred to as arabinoxylans, (glucurono) arabinoxylans, or heteroxylans, depending on the nature of the side chains along the xylan backbone. One of the most unique aspects of these xylans is the presence of feruloyl cross links. In their native structure, these cross links serve to provide structure and rigidity to the cell wall.
Hemicellulose- Beta- Glucan Both cellulose and beta-glucan are similar -both β-linked glucans; cellulose forms rigid water-insoluble microfibrils, while β -glucan is water soluble. The water solubility of β -glucans is due to glycosidic linkages, which, depending on source, can differ markedly. The most important and widely studied β -glucans, are the cereal β -glucans that are found in the highest concentrations in oats and barley. This - β glucan is a linear polysaccharide consisting of β -(1 4) linkages, which are interrupted usually every 2 4 glucose units by a β (1 3) linkage. Bacteria can also produce β -glucans, the most prevalent of which is curdlan, -- linear homo polysaccharide of β (1 3)-linked glucopyranosyl units., also produced by some types of algae. Some yeast and mushrooms produce a β -glucan consisting of a β - (1 3) linked backbone, with β -(1 6)-branches on about 5% of the glucose units. These differences in structure affect the physiological properties
Lignins This substance is the only non carbohydrate type of dietary fiber. It is a large compound that forms the woody part of plants. In the intestine, it combines with bile acids to form insoluble compounds, thus preventing their absorption. Lignin is a complex polymer of phenylpropane units, which are cross-linked to each other with a variety of different chemical bonds. lignins arise from radical coupling reactions of three primary precursors, the monolignols p-coumaryl, coniferyl and sinapyl alcohols.
Nutritional value and energy regulation Not considered to have a significant nutritional value for long Many are fermented in the large intestine to produce hydrogen, methane, carbon dioxide, and short-chain fatty acids. SCFA are rapidly absorbed from the gastrointestinal tract. an average of 2 kcal/g fiber. Actual values range from 0 to 3 kcal/g for no fermentable and highly fermentable fibers, respectively. capacity of both soluble and insoluble fibres to bind water leads to an additional lowering of the energy-to-weight ratio resulting in reduction of voluntary energy intake
The physical properties of TDF in terms of solubility / insolubility Relative solubility and functionality of soluble dietary fiber is affected by their Polymer size Molecular weight distribution Functionality of insoluble dietary fibers affected by Particle size Distribution Other key physical properties which are better predictors of physiological function Water binding and capacity to swell Bulk volume density Gelation /viscosity Oil absorption (bile acid binding ability) Cation exchange capacity Particle size Color and taste / odour Microbial degradation
Physicochemical Properties of DF -viscosity Pectins, β-glucans, various gums and algal polysaccharides are capable of forming highly viscous solutions. Viscosity results in poorer mixing of enzymes and substrates and affects delivery of absorbable nutrients to the mucosal cells. the presence of highly viscous materials in the stomach and small intestine slows the digestion and absorption of nutrients. Viscous polysaccharides blunt the appearance of glucose in the plasma when included in a glucose tolerance test, and they can delay the disappearance of starch from the small intestine. The effects of fiber are most likely related to the viscosity of their fiber sources
Physicochemical Properties of DF - Water holding capacity(whc) WHC measures the ability of a fiber to hold water and is related to solubility of the polysaccharide. Pectin s, gums, α-glucans and certain hemicelluloses have a high WHC. WHC has an important relationship with several of the physiologic effects of fibers. For a polysaccharide to become viscous in the gut it must have a high solubility and WHC, within the large intestine, a high WHC facilitates degradation of the polysaccharides by allowing greater penetration of microbes into the polysaccharide structure. WHC also contribute to faecal bulking of a fiber by holding water in the faecal residue. Water laden sponge
Physicochemical Properties of DF -Bile acids binding capacity wheat bran, guar-gum, isolated lignin have been shown to bind bile acids in the small intestinal contents pectin, guar-gum, oat bran and wheat bran have shown to increase fecal bile acid excretion in humans been Bile binding capacity of the fibers cause increase in the excretion of bile acids and also the turnover of cholesterol and contribute to the ability of certain fibers to lower plasma cholesterol bile acids and phospholipids are required for micelle formation and the subsequent digestion and absorption of lipids interaction of certain fibers with bile acids and phospholipids slows lipid digestion and absorption
Physicochemical Properties of DF - Particle size it plays in controlling a number of events occurring in the digestive tract -transit time, - fermentation, - faecal excretion
Microbial degradation and Short Chain Fatty Acids (SCFA) The polysaccharides in the dietary fiber helps for the growth and metabolism of the micro flora normally present in the human large intestine. micro flora, has the important function of degrading residual food components and endogenous secretions that enter the large intestine. carbondioxide, hydrogen, methane and SCFA are the degraded prodcuts acetate, butyrate and propionate are the major anions. The increase in stool weight due to consumption of fiber from fruits or vegetables is due primarily to an increase in the microbial mass of feces. microbial degradation of fiber is an important determinant of the fecal bulking ability of fiber sources.
Physicochemical Properties of DF -Short Chain Fatty Acids (SCFA) Daily SFCA production is 200 to 300 m mol absorbed rapidly and the postal concentrations in fed subjects is about 400 m/l Colonocytes metabolize SCF as an energy source and butyrate may be the primary energy source for cells in the more distal colon of humans Propionate enters the portal blood and is cleared by the liver. Propionate may have significant metabolic effects on hepatic lipid or glucose metabolism. Acetate, which is the predominant SCFA produced can be rapidly metabolized to CO 2 by peripheral tissues.
Physiological actions of TDF in alimentary tract Physiological parameters of TDF may be considered on the basis of its progress through the alimentary tract as follows: Mouth and stomach Chewing Salivation satiation satiety Gastric emptying Small intestine Digestion of macro nutrients Absorption of nutrients Bile acid re-absorption Intestinal morphology Intestinal cell proliferation
Physiological actions of TDF in alimentary tract contd.. Large intestine / colon Stool weight water content / dilution transit time stool frequency Laxation micro flora Fermentation SCFAs production colonic cell proliferation / morphology Blood / hepatic metabolism Post Prandial serum-glucose and hormone levels Serum lipids (eg. Cholesterol concentration)
Cardiac health and lipid profile High levels of dietary fiber intake are associated with lower prevalence rates for CHD stroke, and peripheral vascular disease major risk factors, hypertension, diabetes, obesity, and dyslipidemia, are less common in individuals with the highest levels of fiber consumption. High levels of fibre intake and whole grains are associated with lower risk of CHD. 29% Lower CHD prevalence was lower in the group with highest intake of dietary fibre than with those with lowest intake(cohort studies 158,000 individuals 26% reduction in prevalence of ischemic strokes. lower serum LDL-cholesterol values Soluble fibre lower systolic blood pressure and total cholesterol values. sustain significant hypocholesterolemic effects for long-term periods
Glycemic index and diabetes DF modify glycemic response and useful in the diabetic diet. high glycemic index Foods cause a sharp rise in blood glucose low glycemic index foods moderate rise in blood glucose. High DF intake play a significant protective role with respect to diabetes that is independent of other dietary factors. 25 50 g/day, (15 25 g/1000 kcal) was recommended In India ICMR revised the dietary fibre requirement from 30 to 40 g/day
Diverticulosis, and Diverticulitis It is an out pouching due to reduced faecal bulk Adequate fiber intake increases faecal bulk and reduce the incidence of diverticulosis. The physical attributes of fiber contribute to the ability to alter the bulk and composition of faeces as well as its transit time. Major bulking agents-cellulose, hemicelluloses, and lignin Aging decreases the integrity of the colon wall - adequate DF reduces chances of diverticular disease Diverticulitis infected diverticula
Irritable bowel syndrome (IBS) It Is a general term for a wide range of gastrointestinal disorders Both diarrhoea and constipation are the symptoms of IBS along with abdominal pain or bloating. Wheat bran and Ispaghula are often prescribed for treatment of IBS. Particularly in constipated individuals, this treatment provides symptomatic relief. In some individuals, wheat bran exacerbate symptoms.
Colon cancer Binding of dietary carcinogens Lignin helps free radical scavenging phenolic groups within lignin facilitate this activity Alters the colonic ph or modifying the metabolic by-products of intestinal flora thus helps risk reduction of cancer butyric acid a metabolic by-product that has great role Butyric acid is a volatile fatty acid produced after fermentation of dietary fiber by the microflora in the colon. volatile fatty acid stimulates apoptosis of cancerous colon cells in vitro, Provide potential mechanism for inhibiting multiplication of carcinogenic cells
Limitations of dietary fibre suggested intake 30g/day, Revised to 40g/day by ICMR in 2010 Beyond RDA - chelation of micronutrients produce phytobezoars potentially resulting in gastrointestinal obstruction. Balancing the fibre intake slow increase of the fibre quantity is recommended.