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Sucrose

by demiguin


 I.  Introduction

Sucrose or simply table sugar is the most abundant disaccharide in nature.  Together with fructose, they are the most common natural sweeteners.  Sucrose is present in all photosynthetic plants.  This means that the fruits and vegetables that we eat all have sucrose in their composition.  Although sucrose is available in numerous sources, its most commercial sources are sugar canes and sugar beets.  Sugar canes are 20% sucrose by weight and sugar beets are 15% sucrose by weight.

 

II. Discussion

            Earlier, we said that sucrose is “the most abundant disaccharide in nature”.  By disaccharide, we mean that it contains two Monosaccharide units joined together by a glycosidic bond.  Specifically, it is composed of 1 molecule of D-glucose and 1 molecule of D-fructose.  Sucrose differs from other disaccharides in that its glycosidic bond is formed between Carbon 1 of (the acetal carbon) of glucose and Carbon 2 (the acetal carbon of fructose).  This means that sucrose has no hemiacetal group but has 2 acetal groups.  In some books, sucrose is also considered as an Oligosaccharide (2-10 Monosaccharides) and in other it is not (4-10 Monosaccharides).

            We have used the term “Saccharide”, but what does it really mean?  Saccharides are usually used to describe carbohydrates.  Saccharide is a Greek term meaning something sweet.  For the case of carbohydrates, this is a misnomer since not all carbohydrates are sweet.  The term however can be used conveniently when we are talking about individual carbohydrate units.  These are the Monosaccharides, Oligosaccharides, and Polysaccharides (more than 10 units)

            Although sucrose is said to be natural and abundant, we could rarely see it as an ingredient in diet softdrinks and other products.  “Sugar free” products do not normally have sucrose.  What is being used instead of sucrose are what we call synthetic sugars.  They are used primarily used by diabetics, weight-watchers and health conscious individuals.  The reason for this is that sucrose contributes more calories to a person’s diet than synthetic sugars.  It is not that synthetic sugars have fewer calories than sucrose.  The truth is that these synthetic sugars have about the same amount of calories per gram as regular sucrose. (In the case of Xylitol, used as a sweetener in “sugarless gum”)  It is just that these synthetic sugars are a lot sweeter than sucrose that only a small amount of them are needed to sweeten foods and beverages.  The small amount would only contribute a negligible amount of calories. 

 

Below is a table comparing the sweetness of some natural sugars and some synthetic sugars to sucrose.

 

Name

Type

Sweetness

Lactose

Disaccharide

0.16

Glucose

Monosaccharide

0.75

Sucrose

Disaccharide

1.00

Fructose

Monosaccharide

1.75

Aspartame

Synthetic

180

Acesulfate Potassium

Synthetic

200

Saccharin

Synthetic

350

 Please note that none of the synthetic sugars listed in the above table have any structural resemblance to carbohydrates.

            Saccharin is the oldest synthetic sugar.  Other books state that saccharin is 300 times sweeter than sucrose.  It is also said to have metallic after taste.  Saccharin was  banned in 1970 because it was said to cause cancer.

            Aspartame, sold under the brand name Nutrasweetâ was an enormous success.  Other books state that Aspartame is 100 times sweeter than Sucrose.  Others state that it is 180 times sweeter.  Aspartame is the methyl ester of a dipeptide formed from the amino acids Aspartic acid and Phenylalanine.  Since both of these amino acids occur naturally and are both part of nearly every protein, there was not much concern about its health effects, although it was still tested. If you would notice, there are more “diet” drinks rather than “diet” snacks like biscuits and breads.  One reason for this is that Aspartame decomposes with heat. Which means that it cannot be used sensibly in baking and cooking.

Acesulfate-K or Acesulfate Potassium has been recenty approved.  It is more popularly used in softdrinks since it has little aftertaste. It is used with Aspartame to sweeten different products. A good example would be Coke Light (previously known as Diet Coke).

There are still other synthetic sugars available.  We are no longer limited to using just plain table sugar.  Other sugars include:

v     Alitame, which is 2000 times sweeter than sucrose. (a pound of Alitame is worth a ton of sucrose).  It is also more stable to hydrolysis than aspartame.  This means that it could keep its sweetness better.

v     Sucronomic Acid, which is 200,000 times sweeter than sucrose. 

v     An additional example would be Sucralose which has been approved by the U.S. Food and Drug Administration.  Sucralose is 600 times sweeter than sucrose and it looks and tastes like sugar.  This could actually replace sucrose in baking and cooking since it is stable at those temperatures.  Sucralose neither promote tooth decay nor provide much calories.

Another benefit of these sugars is that diabetics can now enjoy sweet food and drinks without worrying about their health.  Since diabetics are trying to eliminate excessive amounts of glucose in their body, and sucrose comprises fructose and glucose, synthetic sugars would actually be sensible alternatives.

Given the said benefits of artificial sweeteners, there is still a down side.  Synthetic sugars are simply more expensive than sucrose.  They are also less abundant.  The most popular artificial sweetener is Aspartame.  This, however, cannot be taken by people suffering from Phenylketenuria.  This is because their metabolism causes a buildup of Phenylpyruvic acid derived from Aspartame.

 III.  Sources

v     Maitland Jones Jr. Organic Chemistry, ã1997 by W.W. Norton and Company

v     Joseph M. Hornback. Organic Chemistry, ã1998 Brooks/Cole Publishing Company

v     John Mcmurry. Organic Chemistry (5th Ed.), ã2000 Brooks/Cole Publishing Company

v     Philip S. Bailey Jr. and Christina A. Bailey. Organic Chemistry: A Brief Survey of Concepts and Applications, ã2000 Prentice-Hall, Inc.

v     William H. Brown.  Introduction to Organic Chemistry, ã1997 Sauders College Publishing

v     Graham Solomons and Craig Fryhle.  Organic Chemistry (7th Ed), ã2000 John Wiley and Sons


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