CARBOHYDRATESCarbohydrates: Classification, structure, general properties and functions of mono - , oligo-,

(Disacharides), and polysaccharides. Complex carbohydrates, mucopolysaccharides, amino sugars, bacterial cell wall sugars, proteoglycans, glycoproteins, blood sugar compounds. Brief

account of various quantitative and qualitative methods of estimation.

Sweetness of sugar and Non Caloric Sweeteners: Relative to Sucrose

Sugar Relative Sweetness

Sugars

D- LactoseD- Galactose

0.160.32

D- Maltose 0.32

D-Xylose 0.40

D-Glucose 0.74

Sucrose 1.0

Invert Sugar 1.23

D-Fructose 1.73

Sweeteners

Sucaryl Sodium 30

Aspartame 180

Saccharin 400

Monellin (Protein Sweetner; Sap of serendipity berries) 2000

There are two functionally different classes of disaccharides:

Reducing disaccharides, in which one monosaccharide, the reducing sugar of the pair, still has a free hemiacetal unit that can perform as a reducing aldehyde group;cellobiose and maltose are examples of reducing disaccharides, each with one hemiacetal unit, the other occupied by the glycosidic bond, which prevents it from acting as areducing agent.

Non-reducing disaccharides, in which the component monosaccharides bond through an acetal linkage between their anomeric centers. This results in neither monosaccharide being left with a hemiacetal unit that is free to act as a reducing agent. Sucrose and trehalose are examples of non-reducing disaccharides because their glycosidic bond is between their respective hemiacetal carbon atoms. The reduced chemical reactivity of the non-reducing sugars in comparison to reducing sugars, may be of advantage where stability in storage is important

Amylose:

• Simpler structure and more soluble in water• (separated partially by keeping in hot water)

• Amylose is soluble without swelling in hot water

• Readily dispersed in water but does not form characteristic gel or starch pest

• Produced typical Blue colur

Glycogen-

Particle size smaller then starch grain

Not amylose

Chain are shorter- 10-20 glucose unit

Highly branched and more compact

More soluble in water then amylopectin

Iodine test

The iodine test is used to test for the presence of starch. When treated with IKI solution—iodine dissolved in an aqueous solution of potassium iodide—the triiodide anion (I3

−) complexes with starch, producing an intense blue/purple colour. However, the intensity of the color decreases with increasing temperature and with the presence of water-miscible organic solvents such as ethanol. The test cannot be performed at very low pH due to the hydrolysis of the starch under these conditions.[1]

Cellulose : b-D glucosePectin : Polygalacturonic AcidIn plant biology, pectin consists of a complex set of polysaccharides (see below) that are present in most primary cell walls and are particularly abundant in the non-woody parts of terrestrial plants. Pectin is a major component of the middle lamella, where it helps to bind cells together, but is also found in primary cell walls.The amount, structure and chemical composition of pectin differs among plants, within a plant over time, and in various parts of a plant. Pectin is an important cell wall polysaccharide that allows primary cell wall extension and plant growth. During fruit ripening, pectin is broken down by the enzymes pectinase and pectinesterase, in which process the fruit becomes softer as the middle lamellae break down and cells become separated from each other.[4] A similar process of cell separation caused by the breakdown of pectin occurs in the abscission zone of the petioles of deciduous plants at leaf fall.[citation needed]

Pectin is a natural part of the human diet, but does not contribute significantly to nutrition. The daily intake of pectin from fruits and vegetables can be estimated to be around 5 g (assuming consumption of approximately 500 g fruits and vegetables per day).In human digestion, pectin binds to cholesterol in the gastrointestinal tract and slows glucose absorption by trapping carbohydrates. Pectin is thus a soluble dietary fiber.Consumption of pectin has been shown to reduce blood cholesterol levels. The mechanism appears to be an increase of viscosity in the intestinal tract, leading to a reduced absorption of cholesterol from bile or food. [5] In the large intestine and colon, microorganisms degrade pectin and liberate short-chain fatty acids that have positive influence on health (prebiotic effect).[citation needed]

Bacterial cell wall sugars: Peptidoglycan Structure

Nearly all bacterial cell walls

Enormous meshlike structure often referred to as the peptidoglycan sacculus.

Peptidoglycan is composed of many identical subunits

Sacculus contains two sugar derivatives

• N-acetylglucosamine (NAG)

• N-acetylmuramic acid (NAM)

Several different amino acids.

Peptidoglycan: a rigid framework of polysaccharide crosslinked by short peptide chains. Some bacteriapossess a lipopolysaccharide- and protein-rich outer membrane

Mechanical support, shape, and protection againstswelling in hypotonic media. The cell wall is aporous nonselective barrier that allows most smallmolecules to pass

The peptidoglycan sacculus is strong but elastic. I is able to stretch and contract in response to osmotic pressure.

Peptidoglycan sacculi are also rather porous, allowing globular proteins having a molecular weight as large as 50,000 to pass through, depending on whether the sacculus isrelaxed or stretched; thus only extremely large proteins are unable to pass through peptidoglycan. Variants of peptidoglycan are ofen characteristic of particular groups and are therefore of some taxonomic value.

Peptidoglycan can also vary in terms of the length of the peptidoglycan strands and the amount of cross-linking

Bacteria that stain Gram positive tend to have much more cross-linking, whereas those thatstain Gram negative have considerably less.

Carbohydrates and Blood Sugar

When people eat a food containing carbohydrates, the digestive system breaks down the digestible ones into sugar, which enters the blood.•As blood sugar levels rise, the pancreas produces insulin, a hormone that prompts cells to absorb blood sugar for energy or storage.•As cells absorb blood sugar, levels in the bloodstream begin to fall.•When this happens, the pancreas start making glucagon, a hormone that signals the liver to start releasing stored sugar.•This interplay of insulin and glucagon ensure that cells throughout the body, and especially in the brain, have a steady supply of blood sugar.Carbohydrate metabolism is important in the development of type 2 diabetes, which occurs when the body can’t make enough insulin or can’t properly use the insulin it makes.•Type 2 diabetes usually develops gradually over a number of years, beginning when muscle and other cells stop responding to insulin. This condition, known as insulin resistance, causes blood sugar and insulin levels to stay high long after eating. Over time, the heavy demands made on the insulin-making cells wears them out, and insulin production eventually stops.

In the past, carbohydrates were commonly classified as being either “simple” or “complex,” and described as follows:

Simple carbohydrates:These carbohydrates are composed of sugars (such as fructose and glucose) which have simple chemical structures composed of only one sugar (monosaccharides) or two sugars (disaccharides). Simple carbohydrates are easily and quickly utilized for energy by the body because of their simple chemical structure, often leading to a faster rise in blood sugar and insulin secretion from the pancreas – which can have negative health effects

These carbohydrates have more complex chemical structures, with three or more sugars linked together (known as oligosaccharides and polysaccharides).  Many complex carbohydrate foods contain fiber, vitamins and minerals, and they take longer to digest – which means they have less of an immediate impact on blood sugar, causing it to rise more slowly. But other so called complex carbohydrate foods such as white bread and white potatoes contain mostly starch but little fiber or other beneficial nutrients.Dividing carbohydrates into simple and complex, however, does not account for the effect of carbohydrates on blood sugar and chronic diseases. To explain how different kinds of carbohydrate-rich foods directly affect blood sugar, the glycemic index was developed and is considered a better way of categorizing carbohydrates, especially starchy foods

Complex carbohydrates:

Glycemic index

The glycemic index ranks carbohydrates on a scale from 0 to 100 based on how quickly and how much they raise blood sugar levels after eating. Foods with a high glycemic index, like white bread, are rapidly digested and cause substantial fluctuations in blood sugar. Foods with a low glycemic index, like whole oats, are digested more slowly, prompting a more gradual rise in blood sugar

•Low-glycemic foods have a rating of 55 or less, and foods rated 70-100 are considered high-glycemic foods. Medium-level foods have a glycemic index of 56-69.•Eating many high-glycemic-index foods – which cause powerful spikes in blood sugar – can lead to an increased risk for type 2 diabetes, (2) heart disease, (3), (4) and overweight, (5,6) (7). There is also preliminary work linking high-glycemic diets to age-related macular degeneration, (8) ovulatory infertility, (9) and colorectal cancer. (10)•Foods with a low glycemic index have been shown to help control type 2 diabetes and improve weight loss.•A 2014 review of studies researching carbohydrate quality and chronic disease risk showed that low-glycemic-index diets may offer anti-inflammatory benefits. (16)•The University of Sydney in Australia maintains a searchable database of foods and their corresponding glycemic indices.

Many factors can affect a food’s glycemic index, including the following:•Processing: Grains that have been milled and refined—removing the bran and the germ—have a higher glycemic index than minimally processed whole grains.•Physical form: Finely ground grain is more rapidly digested than coarsely ground grain. This is why eating whole grains in their “whole form” like brown rice or oats can be healthier than eating highly processed whole grain bread.•Fiber content: High-fiber foods don’t contain as much digestible carbohydrate, so it slows the rate of digestion and causes a more gradual and lower rise in blood sugar. (17)•Ripeness: Ripe fruits and vegetables tend to have a higher glycemic index than un-ripened fruit.•Fat content and acid content: Meals with fat or acid are converted more slowly into sugar.

Molisch’s Test

2-3 drops of beta-naphthol   solution are added to 2ml of the test solution. Very gently add 1ml of Conc. H2SO4 along the side of the test tube..    

A deep violet   coloration  is produced at the junction of two layers

This is due to the formation of an unstable condensation product of beta-naphthol with furfural (produced by the dehydration of the carbohydrate). 

Fehling's test

About 2 ml of sugar solution is added to about 2 ml of Fehling’s solution taken in a test-tube. It is then boiled for 10 min

Presence of reducing sugar

A red precipitate is formed

This is due to the formation of cuprous oxide by the reducing action of the sugar.

Benedict’s test

To 5 ml of Benedict's solution, add 1ml of the test solution and shake each tube.  Place the tube in a boiling water bath and heat for 3 minutes.  Remove the tubes from the heat and allow them to cool. 

Presence of reducing sugars

Formation of a green, red, or yellow precipitate

If the saccharide is a reducing sugar it will reduce Copper [Cu] (11) ions to Cu(1) oxide, a red precipitate

Barfoed’s test

To 2 ml of the solution to be tested added 2 ml of freshly prepared Barfoed's reagent.  Place test tubes into a boiling water bath and heat for 3 minutes. Allow to cool.

A deep blue colour is formed with a red ppt. settling down at the bottom  or sides of the test tube.

Presence of reducing sugars. Appearance of a red ppt as a thin film at the bottom of the test tube within 3-5 min. is indicative of reducing mono-saccharide. If the ppt formation takes more time, then it is a reducing disaccharide.

If the saccharide is a reducing sugar it will reduce Cu (11) ions to Cu(1) oxide

Seliwanoff test

To 3ml of of Seliwanoff’s reagent, add 1ml of the test solution.  Boil in water bath for 2 minutes.

A cherry red colored precipitate within 5 minutes is obtained.

A faint red colour  produced

Presence of ketoses[Sucrose gives a positive ketohexose test ]

Presence of aldoses

When reacted with Seliwanoff reagent, ketoses react within 2 minutes forming a cherry  red condensation product

Aldopentoses react slowly, forming the coloured condensation product.

Bial's test

Add 3ml of Bial’s reagent to 0.2ml of the test solution. Heat the solution in a boiling water bath for 2 minutes

A blue-green product 

A muddy brown to gray product

Presence of pentoses.

Presence of hexoses.

The furfurals formed produces condensation products with specific colour.

Osazone Test

Two two ml of the test solution, add 3ml of phenyl hydrazine hydrochloride solution and mix. Keep in a boiling water bath for 30mts. Cool the solution and observe the crystals under microscope

Formation of beautiful yellow crystals of osazone

Needle shaped crystals

Hedgehog crystals

Sunflower shaped crystals

Glucose/fructose

Presence of lactose

Presence of maltose

Reducing sugars forms ozazone on treating with phenylhydrazine