Monosaccharide’s are simple carbohydrates that cannot be hydrolised into simpler compounds. Glucose, fructose and galactose are three nutritionally important carbohydrates in this category.
Glucose which is also called dextrose, grape sugar or corn sugar is widely distributed in nature. In plants it is found in sweet fruits, Vegetables and sap. It is somewhat less than cane sugar and is abundant in sweet fruits such as grapes, berries and oranges, and in some vegetables, such as sweet corn and carrots. It is also found in corn syrup (commercially prepared), honey and molasses. In the animal body it is the end product of the digestion of starch, sucrose, maltose and lactose.
Glucose has an important function in the blood of animals and man where it serves as a source of immediate energy for the body cells and tissues. The normal level of blood glucose in the human body is 80 mg per 100 ml of blood. The balance of glucose level in the blood is important and when the body is unable to use the glucose, this level increases causing a disorder called diabetes. Blood glucose comes from dietary carbohydrates, stores of glycogen in the body of from the synthesis of carbohydrates.
Fructose, also called laevulose or fruit sugar is highly soluble in water and does not readily crystallize. It is much sweeter than cane sugar and is found in the nectar of flowers, ripe fruits and some vegetables. It is also produced during the hydrolysis of sucrose. Honey contains 40% fructose and molasses 8%.
Galactose does not occur free in nature. It is produced in the body during the digestion of the disaccharide lactose.
Both fructose and galactose have the same chemical formula as glucose (c6h12o6), but differs in the arrangement of chemical groups in the chemical chain.