Types of Carbohydrates: Sugars, Starches, Fibres
Carbohydrates contain carbon (C), hydrogen (H), and oxygen (O) as elements. Usually carbon and hydrogen ratio is 2:1. There are three main types of carbohydrates as sugars, starches and fibres. Sugars are simple carbohydrates and starch and fibres are complex carbohydrates. In this tutorial, we are going to study about types of carbohydrates;sSugars, starches and fibres
Sugar
Sugars are monosaccharides and oligosaccharides. Monosaccharides contain one sugar unit. Monosaccharides can be categorized as triose, tetrose, pentose and hexose which have 3,4,5,6 carbon atoms respectively. Also monosaccharides can be classified into two groups that aldose and ketoses. Glucose is a hexose that is very important to our life. And fructose and also galactose are important too.
Glucose - a type of sugar
Glucose is the main product of photosynthesis. Glucose is one of the most important fuel in human body. Also important to the brain and our nervous system. Food sources of glucose: fruits and vegetables, honey, corn syrup, high fructose corn syrup.
Fructose - a type of sugar
Fructose is the sweetest carbohydrate. Plants make nectar. The nectar has this fructose in high amount. Because of its sweetness the insects attract to those plants. So this factor helps to reproduction. Food sources of fructose: Fruits and vegetables, honey, high fructose corn syrup.
Galactose
Milk contains galactose in greater amount.
More about sugar
- Those carbohydrates that carries aldehyde group are called aldose and ketone group carried Monosaccharides called ketose.
- Oligosaccharides contain more than 2(2-9) sugar units. Oligosaccharides are disaccharides, trisachcharides and also tetrasachcharides.
- Disaccharides have two monosaccharide groups. There are three types of Disaccharides. Maltose, sucrose, lactose. Maltose contain two glucose molecules. They are linked by alpha 1-4 linkages. Maltose are called malt sugar.
- Lactose are made by one glucose and one Galactose and also they linked by alpha 1-4 linkages. Lactose are called milk sugar. Sucrose contain one glucose and one fructose. They linked by alpha 1-2 linkages. Sucrose are called beet/ cane sugar.
- Trisachcharides contain three sugar units. Raffinose that in beans are made by one galactose, one glucose and one fructose. Maltotriose are contained by three glucose units.
- Tetrasachcharides contain four sugar units. Stachyose that in beans have two galactose one glucose and one fructose. sesamose have same units. But the structure of these two are different.
Functional properties of sugars
Sugars are used in confectionery manufacturing as a sweetener. Sugars are dissolves in water well. So sugars are taken to form syrups. High concentrations of sugars are used as preservatives. They contribute to browning reactions in foods.
What is this browning reaction in foods?
Sometimes it is defined as mailad reaction. When there are amino group and carbonyl group of sugars, they reacts together and form a unstable compound called glycosylamine and water. After the rearrangement, aminoketose compounds are occurred. Again the rearrangements are happened. Final product has a fine aroma, colour and flavour. And also it is golden brown colour.
Starch
Starch is a complex carbohydrate. And also a polysaccharide. Starch's repeating unit is alpha D glucose. Amilo pectin and amylose are the two types of starches.
Amylose is a linear one.it has alpha 1-4 linkages. Amylo pectine is a branched one. It has alpha 1-4 linkages and alpha 1-6 linkages. amylo pectin is found mostly than amylose. Starch of food is primarily of plant origin.
Starch is insoluble in cold water, alcohol and other solvents. The basic formula of starch is (C6H10O5)n. starch is used as a thickener. When starch is in hot water, it forms gels and pastes. Starch gels are used in puddings.
What is starch gelatinization?
When we heat up a starch contain substances like flour in a liquid, starch granules start to swell and absorb the liquid. After the volume of starch is increased. Then, the starch is released into the liquid from the starch granules. Because of this, the thickness of the liquid goes high. This is called gelatinization. When we cool the liquid, it forms gels.
Pectins
Pectin is a type of starch.Pectin is made by D- Galactouranic acids. They link together by alpha 1-4 linkages. Pectin consist in the plant cell walls and between plant cell walls. Pectin can combine the plant cell walls together.
80% of the COOH groups of pectin are esterified with methanol in natural pectins. Due to that reason, there are two types of pectins. High methoxyl(HM) pectin and low methoxyl(LM) pectin.
HM has a high degree of esterification than 50%. LM has a low degree of esterification than 50%.
As well as high methoxyl pectins require high soluble solid content(sugar) and low pH value to form a gel. Low methoxyl pectin require Ca and high pH value to form a gel.
Cellulose
It was found that, Cellulose is the most abundant organic polymer in the earth. And also, cellulose is the most abundant carbohydrate. Cellulose is synthesized by plants and also bacteria.( Acetobacter xylinum) Repeating unit of cellulose is D-Glucose. D glucose molecules linked by the beta-1-4linkages. cellulose is a structural material in cell walls of plants and helps plants to keep them stable and strong.
And also cellulose is a water insoluble polysaccharide and it is a dietary fiber. Long cellulose chains join together and form fibres. Cellulose is used to produce paper and paper products as well as cotton, linen. Cellulose can be translated into cellophane and nitrocellulose after they are used to photography.
Humans cannot digest cellulose. Cellulose chain is arranged as a linear one. Cellobiose is the repeating disaccharide unit in the cellulose. Derivatives of cellulose are used in the industry. Derivatives are: carboxymethylcellulose(CMC), hydroxyethylcellulose(HEC), hydroxylpropylcellulose(HPC). But widely used derivative is CMC.
Hemicellulose
Hemicellulose is the second abundant biopolymer in plants. Hemicellulose is made by different monosaccharide units. Not only glucose units, but also pentoses and other hexoses. Hemisellulose includes xylose, mannose, arabinose, Galactose, fructose. Hemicellulose is not a long chain than cellulose. Xylan, xyloglucan, mannan, xylomannan are the hemicellulose types. Hemicellulose is insoluble in water but soluble in aqueous alkali solutions. And also hemicellulose influences the baking characteristics of the flour.
Carbohydrate gums
Carbohydrate gums are polysaccharides and have hydrophilic properties. Seeds, roots, tree sap, bacteria, seaweed are the sources of carbohydrate gums. Starches, pectin, derivative of cellulose are act like carbohydrate gums. Carbohydrate gums are used as a thickener, texturizer, emulsifier, stabilizer in food industry. Carbohydrate gums are hydrocolloids. Carbohydrate gums protect the colloidal nature of chocolate milk and also break the colloidal nature in wines and beers.
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