Plant-based foods are the primary source of carbohydrates. They are called carbohydrates (hydrates of carbon) because they have the empirical formula Cn(H2O)n. The basic unit of a carbohydrate is a monosaccharaide. The most common monosaccharide is glucose. Glucose is made from plants during the process of photosynthesis. During this process, plants use light (photo) to synthesize (make) glucose by combining water from the soil and carbohydrates that animals exhale. In the process, glucose is made, along with oxygen that animals can use for respiration. 

Glucose is referred to as a monosaccharide since it consists of only one saccharide (sugar) unit. Two monosaccharides connected is called a disaccharide. Three is called a trisaccharide. Four to 19 monosaccharides produce an oligosaccharide. Above that, we refer to the carbohydrate as a polysaccharide. 

  • Monosaccharides: glucose, fructose, galactose
  • Disaccharides: lactose (glucose + galactose), sucrose (fructose + glucose), maltose (glucose + glucose)
  • Polysaccharides: starch, soluble and insoluble fiber (e.g. pectin, cellulose, hemicellulose, gums) 

Properties of Mono and Disaccharides

Mono and disaccharides; referred to simply as sugars, provide a ready source of energy to the body since they are easily broken down and absorbed. Too much sugar consumption can lead to obesity which can predispose you to Type II diabetes. This is a type of diabetes where glucose cannot be efficiently removed from the blood stream due to insulin resistance. Sugars provide sweetness to foods. However, all sugars do not have the same level of sweetness. Some are sweeter than others, even if you add the same amount to your food. There sweetness index range in the following order:

  1. Fructose: 173
  2. Sucrose: 100
  3. Glucose: 74
  4. Maltose: 32
  5. Lactose: 16

Sugars are also a source of energy in fermentation processes such as in wine, beer, yogurt and bread making. For example, in wine and beer making yeast consume sugars to produce carbondioxide and alcohol. In bread making yeast consume sugars to produce carbondioxide, alcohol and other flavors characteristic of bread. In yogurt making, bacteria consume lactose to produce lactic acid and flavor compounds. 

Sugars are used to produce brown colors in food through two main processes; caramelization and Maillard reaction. In caramelization, sugars breakdown at high heat (>230oF) and reform to produce new dark polymer compounds and flavors characteristic of caramel. Maillard reaction is a process where sugars react with proteins in foods to produce dark color compounds. Although Maillard reaction can occur at any temperature, it is accelerated at high temperatures. The brown crust on bread, the brown color you get during frying, and the grill marks on grilled meat is due to Maillard reaction. 

Sugar also plays an essential role in controlling viscosity. More sugar will make foods thicker e.g. corn syrup is viscous (thick) since it has a high concentration of sugar relative to water. Adding sugar to foods can provide preservation by lowering water activity and starving microorganisms of water. Higher sugar content reduce the freezing point of water, leading to resistant to freezing and hence softer textures as seen in icecream. Finally, sugar can provide texture. In jam and jelly production they bind water, and helps in gel formation.  

Properties of Polysaccharides: Insoluble and soluble Fiber, Starch and Gums 

Insoluble fiber such as cellulose are complex polysaccharides that helps to improve bowel movement. We can’t harvest energy from cellulose, however some bacteria in our gut can partially ferment them to produce health-promoting short chain fatty acids and intestinal gas. Soluble fiber such as pectin and hemicellulose (e.g. beta-glucan) absorb water and slows down movement of food through the gut, allowing for longer gut fermentation and water reabsorption. 

Cellulose may be added to food to improve fiber content e.g. adding wheat bran to white flour. They may also be chemically modified to produce new functional properties such as increased water absorption and thickening properties. Pectin is mostly used in the production of jams and jellies where they provide gel structure. 

Starch is another complex polysaccharide. It is broken down to release glucose in the body through the action of an enzyme called alpha-amylase. In food, starch exists in the form of granules (capsules containing amylose and amylopectin). Starch is insoluble in cold water but when heat is applied, the granules absorb water, swell and eventually burst, becoming gelatinized. Because of their ability to absorb water when heated, starch is used as a thicker in food.  

Like starch, gums are complex polysaccharides. Because of their bulky nature, they are also used as thickeners in food. Common ones used include carrageenan, xanthan gum, guar gum and locust bean gum. These differ in chemical properties such as degree of gelling and temperature sensitivity. 

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Courtney Simons
Courtney Simons
Author, Dr. Courtney Simons has a Bachelor of Science in Food Science and a Ph. D. in Cereal Science from North Dakota State University.