Updated: Jun 20
Carbohydrate is the body's most essential and prominent energy-providing food class. Carbohydrates rank higher in supplying energy that the body prefers to use for work. Although fats provide more energy of about 9 calories per gram as against 4 calories per gram from carbohydrates and proteins, carbs are the most sought after. Compared to other macronutrients, dietary carbohydrates account for 40 and 80 per cent of all energy intake. The remaining 20 per cent comes from fats and protein during prolonged fasting or extreme starvation.
Scientifically, carbohydrate compounds come in various molecular sizes and shapes. They range from simple units to complex polymers which are a product of thousands of simple units.
There are always two groups in the dietary carbohydrates family; The digestible and the indigestible ones. The digestible carbohydrates can be broken down by the body's digestive enzymes and actions to supply energy and other benefits to the body. While the indigestible ones cannot be digested by the body or used to provide energy to the body. However, indigestible carbohydrates are the chief source of dietary fibre.
Aside from their nutritional values, dietary carbohydrates are also used in food production industries as stabilizers, thickeners, sweeteners, fats replacers, gelling agents, etc. It is safe to say that the very many ranges of convenience food products that are in the world today are a result of the inclusion of carbohydrates. Let us look at the classification of Carbohydrates.
Classifications of Carbohydrate
The different classifications of carbohydrates are;
Monosaccharides (often called simple sugar).
Disaccharides contain two sugar units,
Trisaccharides contain three, and
Oligosaccharides contain several units, and
Polysaccharides are complex polymers. They contain several thousands of units linked together.
Monosaccharides are the most common and simplest carbohydrate unit. Mostly made up of five to six carbon atoms. Sometimes they as well range between three and eight carbon atoms. The most common and important dietary monosaccharides known are glucose, galactose and fructose (the sugars in natural fruits).
The most abundant disaccharide compound are sucrose, lactose and maltose.
Disaccharides contain two monosaccharide units that are joined together by a
linkage, called a glycosidic bond. The most renowned dietary disaccharides are maltose, lactose and sucrose.
Maltose is a disaccharide made in plants. It is formed from two units of glucose joined by an alpha bond. Maltose is the building block for starch. Alpha links or bonds can be broken down by the body, so the starch is readily digested as maltose will be broken into glucose (monosaccharide).
Maltose or malt sugar is formed by the hydrolysis (partial digestion) of starch and glycogen in germinating grains. A process used in making malt and alcoholic drinks.
Lactose is composed of glucose and galactose, bound by the usual glycosidic bond. They are found only in animal (mammalian) milk. They are not found in any plant-based milk. They are the least sweet of the disaccharide family. During digestion, they are broken by the enzyme lactase to form glucose and galactose where they are further used for biological functions. Not every adult human can tolerate mammalian milk which is popularly called diary. It is seen that after being weaned off breastmilk as a child, the ability to process animal milk is impaired in most adult humans. I guess it is because we are humans.
Sucrose which is popularly referred to as table sugar is the most commonly known disaccharide. It is composed of glucose and fructose units that are joined together by glucosidic bonds. The breaking down of sucrose into glucose and fructose can be done by heat or by the enzymes sucrase or invertase. The breaking up of sucrose by invertase is what forms what we know as invert sugar which is an important part of the production of candies and jellies.
Functional Roles of Sugars
Sugars are also used in various functional roles like
The formation of syrups and solutions
Sugars are very soluble in water. The dissolution of sugars in water is what makes syrup. Upon heating again, the water evaporates and crystals are formed. These syrups are mostly used in food industries to add sweetness and enhance the taste of beverages.
Sugars are generally known to be sweet. That is what characterises them the most. Fructose, glucose and sucrose all have some unique sweetness properties. Lactose which is the sugar in milk is the least sweet of all disaccharides. Fructose is the sweetest of all sugars. They are key ingredients in candies and sweets.
Sugar alcohols are formed when sugars are made to go through a reduction reaction. That is replacing a carbonyl group in the sugar structure with a hydroxyl group. This invariably gives rise to the formation of xylitol, sorbitol, and mannitol. All these sugar alcohols are sweet, but none of them is as sweet as sucrose. They are used in producing chewing gums, breath mints and other products that may be kept in the mouth for a while because they do not cause tooth decay.
Sugar alcohols are metabolised less efficiently than sugars, hence, they possess lower caloric values. But that does not say it has no calories even when it is used in products labelled as "sugar-free". Sorbitol as seen follows a different path in its digestion. It is converted to fructose in the body rather than glucose, so they are assumed to be more tolerated by diabetics.
Fermentation is mostly thought of in bread making when sugars are broken down as the yeast feasts on it to produce carbon dioxide which is the leavening agent. The fermentation process also occurs in the human body as we eat carbohydrate foods, and it in turns supplies energy to us for work. A gram of carbohydrate unit supplies 4 calories.
Body and Mouthfeel.
Sugars give the food some viscosity. It makes food less watery or thin, unlike adding non-sugary sweeteners like aspartame or saccharin. They give food a good mouthfeel.
Oligosaccharides contain between three to ten monosaccharide residues that are joined together by glycosidic bonds. Common examples of oligosaccharides are raffinose and stachyose. Raffinose is made up of galactose, glucose and fructose. Stachyose is made up of fructose, glucose and two galactose units. Sachyose and raffinose are usually present in leguminous plant foods like beans and peas.
Oligosaccharides are mostly not digestible by the human digestive system. Hence, they make their way into the large intestine and they serve as food for the good gut bacteria that reside there. The bacteria will feed on it and break it down, converting them to some gases to be later let out. We often refer to oligosaccharides as prebiotics because they are the ones that also supply nutrients to the gut bacteria (probiotics)
Oligosaccharides are a type of carb found in, cabbage, white and red onions, lentils, and other plant foods.
Polysaccharides would contain numerous units of similar monosaccharides, ranging from hundreds to thousands of them.
Starch is a polymer of glucose that contains two types of molecules known as amylose and amylopectin. Amylose and amylopectins are long chains of glucose molecules linked by glycosidic bonds. Amylose is soluble in water because it is linear in structure, while amylopectin is insoluble in water because it has a branched-chain structure. Starch is studied to have either only amylose or only amylopectin.
Foods with starch are mostly root and stem vegetables like potatoes, yam, turnips, beetroots, carrots, cocoyam, sweet potatoes, and some grains like corn, rice, wheat, etc.
Dextrins are intermediate-chain-length glucose polymers formed when starch is broken down or hydrolyzed. They are larger than oligosaccharides and shorter than starch molecules. Dextrins are made up of glucose joined by the legendary glycosidic bonds. They are the carbohydrates produced by the hydrolysis of starch. Such is what is obtained in corn syrup.
Pectins and Other Polysaccharides
Pectins, gums, and seaweed polysaccharides also are important carbohydrates
used in food products. Pectins occur naturally in plant food products, but gums and seaweed polysaccharides do not come from edible plant sources. They are extracted and purified and then added to food products.
Pectins are used as thickeners, stabilizers and gelling agents in jams, jellies ad other foods. Pectins are found mainly in fruits and vegetables as they help to hold plant cells together.
Pectins are water-soluble, and they form gels under the right condition.
Gums are basically extracted from plants. They are gum tragacanth and guar gum.
They are highly branched polysaccharides that form very viscous solutions,
trapping large amounts of water within their branches. Most gums do not form gels. They are useful as thickeners and stabilizers.
Seaweed polysaccharides include agars, alginates, and carrageenans. They
are classified as gums, although they can form gels, unlike most gums.
They are useful as gelling agents, thickeners, and stabilizers in foods.
Cellulose and hemicellulose
Cellulose and hemicellulose are structural polysaccharides that provide support
to plant tissues. Like oligosaccharides, they also are not digested in the body, so they do not contribute to the energy supply in foods. Because they are insoluble, they provide insoluble dietary fibre which is considered a healthy and balanced diet by many scientific, and nutrition standards.
Other nutrients in Carbohydrate-Rish Foods
Carbohydrates foods do not only supply energy for work. Most carbohydrate food sources are having other good amounts of vitamins and mineral nutrients as well. They are particularly rich in phytochemicals which help us to fight pathogens and prevent diseases.
As seen above, we can now affirm that carbohydrates appear in various forms and have many other health-promoting benefits and should not be treated as a villain. Understanding how to employ them in healthy eating is so important and it should be studied for a balanced diet and improved health.