A Review on Dietary Fiber and its Application

 

Subhashis Debnath*, S. Jawahar, H. Muntaj, V. Purushotham, G. Sharmila, K. Sireesha, M. Niranjan Babu

Department of Pharmaceutics, Seven Hills College of Pharmacy, Tirupati, A.P, India

*Corresponding Author E-mail: principal.cq@jntua.ac.in

 

ABSTRACT:

Dietary fiber is that part of plant material in the diet which is resistant to enzymatic digestion which includes cellulose, non cellulosic polysaccharides such as hemi cellulose, pectin substances, gums, mucilageous and a non-carbohydrate component lignin. The diets rich in fiber such as cereals, nuts, fruits and vegetables have a positive effect on health since their consumption has been related to decreased incidence of several diseases. Consumption of dietary fiber rich food has shown many health benefits against a range of disorders including obesity, type 2 diabetes mellitus and colon cancer. Food scientists and technologists then explored the applications of DF (dietary fiber) in a variety of food products through examination and utilization of fibers from various conventional and uncommon sources including agro-food processing by products. The consumption of dietary fiber may affect the absorption of nutrients in different ways. The physicochemical factors of dietary fiber, such as fermentation, bulking ability, binding ability, viscosity and gel formation, water-holding capacity and solubility affect nutrient absorption. The dietary fiber intake influences the different methods in which nutrients are absorbed. The increase in the total fiber content of the diet may delay the glycemic response. Soluble fiber decreased blood glucose content whereas purified insoluble fiber has a little or no effect on the blood glucose levels after a meal.

 

KEYWORDS: Dietary fiber, cellulose, soluble fiber, insoluble fiber.

 

 


INTRODUCTION:

Dietary fiber has been defined as the plant cell polysaccharides and lignin not hydrolyzed by the digestive enzymes of animals and human. However, most appropriate term, which includes all ingested polymers in foods that are not broken down by digestive enzymes in the small intestine, is total dietary fiber (TDF). Therefore Dietary fiber has a physiological effect on human health. Resistant starch (RS) plays a major role in the healthy food industry, because it behaves with properties similar to soluble and insoluble dietary fiber in the gastrointestinal tract.

 

Resistant starch is a fraction of starch escapes enzyme hydrolysis in small intestine and pass to colon or large intestine gastro intestinal. The term ‘dietary fiber’ (DF) was first introduced in 1950s, referring to plant cell wall materials later it was used to describe a class of plant-originated polysaccharides, which cannot be digested and absorbed in the gastro intestinal tract. Dietary fiber has long history, its term originating with Hipsley (1953) who coined dietary fiber as a non-digestible constituents making up the plant cell wall. Botanists define fiber as a part of the plant organs, chemical analysts as a group of chemical compounds, consumer as a substance with beneficial effects on human health and for the dietetic and chemical industries dietary fiber is a subject of marketing. “Dietary fiber consists of remnants of plant cells resistant to hydrolysis (digestion) by the alimentary enzymes of man”, whose components are hemi cellulose, cellulose, lignin, oligosaccharides, pectins, gums and waxes. American Association of Cereal Chemists (AACC) in 2000 defined dietary fiber as the edible parts of plant or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, and lignin1-4.

 

Benefits of dietary fiber:

Digestion:

Insoluble fiber binds to water as it passes through the digestive tract, making stool softer and bulkier. Fiber especially found in whole grain products, helpful in the treatment and prevention of constipation, hemorrhoids and diverticulosis. Diverticula or pouches of the intestaing wall that can be inflamed and painful. This inflammatory condition is called diverticulosis.

 

Cholesterol:

Low blood cholesterol a level has been associated with reduces the risk of coronary heart disease. The body uses cholesterol in the production of bile acids which are excreted daily. The consumption of water soluble fiber binds to bile acids, suggesting that high fiber diet may result in an increased excretion of cholesterol. Some types of fiber appear to have a greater effect than others the fiber found in rolled oats is more effective in lowering blood cholesterol levels than the fiber found in wheat.

 

Cancer:

High-fiber diets may also reduce the risk of developing some types of cancer, especially colon cancer. The idea is based on information that insoluble fiber increases the rate at which wastes are removed from the body. This means the body may have less explosive to toxic substances produced during digestion. The mechanism of fiber consumption may reduce cancer risk are still unknown.

 

Weight loss:

High fiber diets may be useful for people who wish to weight loss. Fiber itself as no calories yet provides a full feeling because of it water absorbing ability.

 

Diabetes and obesity:

Recent researches suggest that a high fiber diet rich in whole grains is associated with a reduced risk for developing type-2 diabetes and obesity. Greater consumption of fiber found in whole grains, compared to refined grains has been shown to modestly reduced glycemic index and improve insulin sensitivity, resulting in an decreased risk for developing type2 diabetes and obesity5,6,7.

 

Basic classification on dietary fiber:

Plant:

Carbohydrates:

a. Cellulose

b. Non cellulose

Ex: Hemi cellulose

      Pectin

      Gum

 

Non carbohydrate

Ex: Lignin

Animal and Microbial origin:

Ex: Xanthan gum

      Chitin

 

Types of dietary fibers:

Dietary fibers are mainly divided into 2 types.

 

Table no: 1Examples of types of dietary fibers

Soluble Dietary Fiber

Insoluble Dietary Fiber

Pectins

Hemi Cellulose

Gums

Mucilages

Cellulose

Lignin

Cutin

 

Fig No 1: Types of dietary fibers

 

Soluble dietary fiber:

It is a food material that is not digestible by appropriately chosen enzymes and is soluble in warm (or) hot water, but is precipitated when that is pre mixed with 4 parts of ethyl alcohol.

 

Gums:

These are complex poly saccharides. It is not part of cell wall structure because they are generally in digestible.  These Gums are present a complex group of highly branched uronic acid containing polymers, mainly

1. Glucoronic acid

2. Galacturonic acid

 

2.a                                      2.b

Fig No 2: Structure of 2.a Glucoronic acid and 2.b Galacturonic acid With neutral sugars such as Xylose, Arabinose and Mannose.

 

These compounds are long chain polymers which dissolve (or) disperse in water to give a thickening or viscosity building effect.

Most Gums are comes from plant material such as

1.     Sea weeds (alginate, agar, and carrageenan)

2.     Seeds (guar gum, locust bean gum)

3.     Tree exudates (gumArabic, gumkaraya, gum tragacanth)

 

Other products of microbial biosynthesis (xanthane gum, gellan gum) and others are produced by chemical modification of natural poly saccharides8,9.

 

β-glucans:

It is present in soluble although small amount may be in- soluble. These are glucose polymers containing unbranched β-1, 4 linked D-glucose units interdispersed with beta-1, 3linkages. The highest concentration are found in barley, rye and oats.

 

Fig No 3: Structure of β glucans

 

Pectins:

These are polymer substances that are based on a polymer of D-glactuoronic acid, linked by α-1,4 linkages. The main polymer has side chains consist of the sugars such as galactose, arabinose and glucose. Pectins are primarily water-soluble, solubility dependent on degree of esterification of galacturonic acid, as well as make up of constituent side chain. The presence of calcium salts enhances the gelling capacity and decreases the dependence on pH and sugar concentration14,15-19.

 

This pectin substances importance as a component of DF because of their ion-exchange due to presence of galacturonic acid units, and gelling.

 

 

Mucilages and Algal Polysaccharides:   

These are found in different parts of plant. These are mixed in storage polysaccharides of plant seeds. Their role is to retain water and protect the seed against desiccation. Mucilages and algal polysaccharides are used in small amounts in the food industry as thickening and stabilizing agents by water-holding capacity and viscous properites10-13.  

 

Insoluble Dietary Fiber: 

Cellulose:

It is least soluble of all fibercomponents; being insoluble not only in cold (or)hot water, but also in hot dilute acid and alkaline as well as cellulose, the major cell wall structural linear configuration, with high degree of inter molecular H-bonding. The β-glucosidic bond between 1, 4linkages of the glucose units can only broken by strong mineral acids and cellulose enzymes. The cellulose is not hydralised in the human digestive system and this property makes cellulose a true available carbohydrate. Controlled as acid hydrolysis of amorphous fraction yield micro crystalline cellulose. Cellulose used as bulky agent in food a due to its water absorbing ability and low solubility.

 

Fig no 4: Structure of cellulose

 

Hemicellulose:

It may present in soluble and in-soluble form and comprised no of branched and liner pentose and Hexose containing poly sachharides. In cereal grains, soluble hemicelluloses are termed “pentosons.” Hemi cellulose dissolved in dilute alkaline. Component monosaccharaides units may include xylose, arabinose, galactose, glucose, mannose, glucuronic acid and galacturonic acid. Both soluble and insoluble hemicelluloses play important role in food products, the former functioning SDF and IDF. They are characterized by their ability to bind water and serve as a bulking agent. Hemi cellulose are fermented as to a greater extent than cellulose in the colon.

 

Lignin:

It is an amorphous, highly water insoluble polymeric material composed of phenyl propane residues which are formed in a matrix type arrangement by the condensation of the phenolic alcohol as such as coniferyl, sinapyl and p-coumaryl. Lignin can bind bile salts and other organic material and may delay or impair the small intestinal absorption of associated nutrients.

 

Cutin and plant waxes:    

These are hydrophobic lipid materials which are typically found in the plant structure, closely associated with the structural poly saccharides. These usually present in present in very small quantities.

 

Dietary fiber is found in fruits, vegetables, legumes, wholegrain breads and cereals. Most sources of dietary fiber tend to have a combination of both soluble and insoluble fiber in varying proportions. Resistant starch is not always measured when fiber is assessed in a food and we may underestimate how much fiber is present in some foods11-15.

 

Table no 2: Fiber content of common foods in the World

Food Serving size

Total dietary fiber (g)

Baked beans ½ cup

6.6

Untoasted Muesli ½ cup

2.7

Green peas ½ cup

3.4

Almonds ⅓ cup

4.0

Wholemeal pasta 1 cup

8.4

Apple with skin 1 medium piece

2.3

Dried Apricots 3 whole

4.5

Carrot, raw 120g (medium)

4.0

Potato, cooked 1 medium (150g)

2.0

Multigrain bread 2 slices

3.1

 

Table no 3: Fiber content of common foods in India. (Nutritive value of Indian foods, NIN)

Cereals

Fiber in g/100g edible portion

Rice

0.2

Wheat

1.2

Bajra

1.2

Maize

2.7

Jowar

1.6

Ragi

3.6

Bengal gram, whole

3.9

Green gram, whole

4.1

Carrot

4.4

Cauliflower

1.2

Lotus stem, dry

25.0

Guava

5.2

Dates fresh

3.7

 

Properties of dietary fiber:

Physico-chemical properties:

Particle size and bulk volume

Characteristic of surface area

Hydration properties

Solubility and viscosity solubility

 

Physical property:

Bacterial degradation

Water holding capacity

Cation exchange capacity

Adsorption of organic materials14,16-28

 

Particle size and bulk volume:

The range of particle size depends on type of cell wall present in food, and their degree of processing. The particle size of fiber may vary during transit in the digestive tract as a result of chewing, grinding and bacterial degradation in large intestine. Beyond 500µm, the hydration properties were found to decrease with decreasein particle size during grinding.

 

Surface area:

The porosity and surface available for bacteria or molecular probes such as enzymes will depend on fiber, which is related to its origin and processing history.

 

Hydration property:

The hydration property determines the fate of dietary fiber in digestive tract. Swelling and water retention capacity provides a general view of fiber hydration and will provide information for supplemented foods. Processes, such as grinding, drying, and heating ex: modifies the physical properties of fiber matrix and also affect the hydration property. The environmental condition such as temperature, pH, and ionic strength, dielectric constant of solution and nature of ions can also influence hydration characteristics of fiber containing poly-electrolytes.

 

Solubility and viscosity solubility:

Solubility has effect on fiber functionality. It is also well established soluble viscous polysaccharides can impede the digestive and absorption of nutrients from the gut. More branching, the presence of ionic groups and potential for inter unit positional bonding increases solubility.

The viscosity of fluid can describes as its resistance to flow. The molecular weight or chain length of fiber increase, the viscosity of fiber in solution increases. The concentration of fiber in solution, temperature, pH, shear condition and ionic strength depends on fiber used.

 

Physical properties:

Bacterial degradation:

Dietary fiber cannot be enzymatically degraded in human small intestine. It is fermented to varying degress by micro flora naturally occurs in large intestine. The degree of degradation various among the poly saccharides and depends on factors such as types, components and poly saccharides structure of DF, water holding capacity physical structure of plants and bacteria flora in large intestine20.

The extent of bacterial degradation of several potential consequences;

1.     Short chain fatty acids (SCFAs) produced during bacterial metabolism may influence physiological responses to fiber. 

Ex: SCFAs can be used by cells in colon for energy and absorption of SCFAs influence hepatic metabolism of lipid and glucose.

2. The fermentation process may lower the pH of large bowl and affect the activity of bacterial enzyme.

 

Water holding capacity (WHC):

It enhanced on poly saccharides by presence of sugar residue with free polar groups. Cellulose and lignin are insoluble and have low WHC. Pectin, gums, β-glucons, mucilages and hemi cellulose have WHC. Hydration of DF results in formation of gel matrix. WHC has also related to fecal bulk. Higher WHC is associated with greater ferment ability of the fiber sources by greater penetration of microbes into polysaccharides structure.

Adsorption of organic material:

It includes bile acids, cholesterol and toxic compounds in DF. In-vitro studies, lignin has effective bile acid adsorbent. Pectin and other acidic polysaccharides also sequester bile acid. In-vivo studies, bile acid adsorption is measured the ability to increase fecal bile acid and steroid excretion.

 

Cation exchange capacity:

The reduced mineral availability and electrolyte absorption associated with certain high fiber diets are undoubtedly due to the binding of minerals and electrolytes of fiber sources. Resulting in increased fecal excretion of minerals and electrolytes.

 

CONCLUSION:

Over the last 20 years in particular there has been an explosion of interest in the area of dietary fiber from the public at large as well as the scientific community to such an extent that dietary fiber is now classed as the sixth major nutrient. The plant material in diet resistant to enzymatic digestion is termed as dietary fibre. It includes cellulose, hemicellulose, pectic substances, gums, mucilages and lignin etc. Dietary habits are major contributors to diabetes. Dietary fibers represent a heterogenous category, and there is still much to understand as to which foods should be preferred to maximize the metabolic effects of fibers, including influences on the gut microbiota. Dietary fibre is naturally present in cereals, fruits, vegetables and nuts. The diets with high content of fibre have been reported to have a positive effect on health.

 

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Received on 27.04.2019         Modified on 23.05.2019

Accepted on 21.06.2019       ©A&V Publications All right reserved

Res.  J. Pharmacognosy and Phytochem. 2019; 11(3):109-113.

DOI: 10.5958/0975-4385.2019.00019.0