Classification and Uses of Sugar

Carbohydrate and Sugars Terminology

Dietary carbohydrate is an important source of food energy, and has a wide range of chemical, physical and physiological properties. Carbohydrate is classified according to chemical composition, but these groupings are not always helpful when describing physical and nutrition functions.  As a result, a number of terms have emerged to group carbohydrates based on physiological properties and to help focus on specific health benefits.

The World Health Organization and Food and Agriculture Organization (WHO/FAO) have recommended that terminology be standardized primarily based on its chemical make-up (i.e., number of sugar units, type of linkage between units). Key terminology used to describe carbohydrate summarized below.

• Carbohydrates
• Sugar
• Sugars
• Other Terminology
• References

Carbohydrates

Carbohydrates contain carbon, hydrogen, and oxygen atoms; in approximately a 1:2:1 molar ratio, giving the general formula C_xH_2xO_x. The ratio of hydrogen to oxygen is always 2:1. General names for carbohydrates include sugars, starches, saccharides, and polysaccharides. The term saccharide is derived from the Latin word "sacchararum" from the sweet taste of sugars. The simplest carbohydrates are monosaccharides (single sugar units) such as glucose, fructose and galactose. Other carbohydrates are composed of monosaccharide units, and break down under hydrolysis. These may be classified as disaccharides, oligosaccharides, or polysaccharides, depending on whether they have two, several, or many monosaccharide units.

Monosaccharides contain one sugar unit and are the building blocks of disaccharides, oligosaccharides and polysaccharides. Principle monosaccharides are glucose, fructose and galactose.

Disaccharides contain two sugar units. In almost all cases one of the sugars is glucose, with the other sugar being galactose, fructose, or another glucose. Common disaccharides are sucrose, lactose and maltose.

Oligosaccharides contain a range of three to nine sugar units, and are often the products of the breakdown of polysaccharides. Common oligosaccharides include raffinose and stachyose.

Polysaccharides contain many sugar units (≥10) in long polymer chains of many repeating units. The most common sugar unit is glucose. Common polysaccharides are starch, glycogen, and cellulose.

A useful classification system recommended by the WHO/FAO, groups carbohydrates according to their degree of polymerization (DP)*, as shown in the table below. 

Despite this classification, controversy still exists over how sugars and carbohydrates are defined. Inconsistency in terminology presents a challenge when comparing and analyzing data that could be used to determine actual intakes or to measure health effects. For example, the WHO/FAO report recommends that the terms "simple" and "complex" carbohydrates should no longer be used; however, this has not been universally accepted.

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Sugars

The term “sugars” refers to all monosaccharides and disaccharides. Therefore, the term “sugars” can be used to describe sugar (sucrose) as well as other types of sugars such as glucose, fructose and lactose. While WHO/FAO categorizes polyols as “sugars” (see table above), the definition of “sugars” in Canada’s Food and Drug Regulations do not include polyols.

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Sugar

Sugar is sucrose, a carbohydrate found in every fruit and vegetable and is the major “disaccharide” (see below) in most diets.  All green plants manufacture sucrose through photosynthesis, the process by which plants transform sunlight into their food and energy supply.  Both sucrose and starch are major carbohydrate end-products of photosynthesis; however sucrose is the major carbohydrate that is transported throughout the plant.  Some plants, such as sugar cane and sugar beet, accumulate high levels of sucrose and as such are used as commercial sources of sugar.  A stalk of the cane plant contains about 14% sugar and sugar beets contain about 19%.

Sucrose is a disaccharide, made up of the two sugar units, glucose and fructose (monosaccharides).  It is present in honey, maple sugar, fruits, berries, and vegetables.  It is also added to food products as crystalline sucrose (granulated, brown sugars) or in liquid form.

In Canada, the Food and Drug Regulations prescribe the standard for sugar as the “food chemically known as sucrose”.  It has a specific compositional standard; i.e. must “contain not less than 99.8% sucrose”.  For food labelling purposes, sugar is considered the “common name” of the food and must meet this standard.  When listed in the ingredient list of a food, different types of sugar can be listed; for example, sugar, liquid sugar, invert sugar or liquid invert sugar.  Compositional standards for other types of sugar are also defined in the Regulations, including: icing sugar, brown sugar, fancy molasses, etc.  All of these types of sugar are derived from sugar cane or sugar beet.

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Other Terminology

In addition to the terminology described above, a number of other chemical and physiological terms are used to describe carbohydrate. A wide range of terms have been reviewed and were considered useful if they were: 1) measurable by a laboratory analyst; 2) understandable to the consumer; and 3) indicative of the properties of the carbohydrates rather than the food itself. (Please see chart below)  It was also noted that grouping carbohydrate by its physical properties or nutritional characteristics is more difficult than classifying by chemical composition because the physiological effects of a particular carbohydrate can vary between individuals. In addition, classification in this manner involves ongoing revision due to the evolving scientific evidence in the area of food science and metabolism.

An Evaluation of chemical and physiological terms used to categorize carbohydrate

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References

Food and Drug Regulations, Department of Justice Canada

Carbohydrate Terminology and Classification. Cumming JH and Stephen AM. European Journal of Clinical Nutrition, 2007, 61:Suppl1: S5-S18

Carbohydrates in Human Nutrition, Report of a Joint FAO/WHO Consultation, 1997

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