Difference Between Sugar and Starch

Main Difference – Sugar vs Starch

Sugar and starch are two types of carbohydrates found in plants and animals. Three types of carbohydrates can be identified as monosaccharides, disaccharides, and polysaccharides. They are made up of three atoms: carbon (C), hydrogen (H) and oxygen (O). Autotrophs produce the simple monosaccharide glucose from carbon dioxide and water during photosynthesis. The combination of two monosaccharides produces disaccharides. Polysaccharides are formed by combining a large number of glucose monomers together. The main difference between sugar and starch is that sugars are disaccharides or monosaccharides whereas starch is a polysaccharide.

This article explains,

1. What is Sugar
– Definition, Structure, Characteristics
2. What is Starch
– Definition, Structure, Characteristics
3. What is the difference between Sugar and Starch

What is a Sugar

Sweet and soluble carbohydrates are generally called sugars. Hence, both monosaccharides and disaccharides are sugars. Monosaccharides have the general chemical formula of (CH₂O)_n. There are three common types of monosaccharides: glucose, fructose, and galactose.

Glucose

Glucose is the organic molecule used in the metabolism as the energy source. Hence, it is very important in physiology, diet, and nutrition in animals. All other forms of carbohydrates are also converted into glucose during digestion. Glucose is more commonly found in ripe fruits and vegetables like beetroot.

Fructose and Galactose

Fructose is the fruit sugar. It is also found in honey. Galactose is present in mammals’ milk.

Figure 1: Glucose, fructose, and galactose

Disaccharides are formed by joining two monosaccharides together with a glycosidic bond. The most common types of disaccharides are lactose, sucrose, and maltose. They have the general formula of C₁₂H₂₂O₁₁. Sucrose is found in sugar cane and sugar beet. It is formed by the joining of a glucose and a fructose molecule together by α(1→2)β bond. Lactose is formed by the joining of a glucose molecule with a galactose molecule by a β(1→4) bond. It is found in mammals’ milk. Maltose is formed by the combination of two glucose molecules together by a α(1→4) bond. It is found in cereals like barley. The structure of sucrose is shown in figure 2.

Figure 2: Sucrose

What is Starch

Starch is the polysaccharide synthesized from glucose by green plants as their main energy store. Plants store starch in staple foods like fruits, tubers like potatoes, seeds like rice, wheat, corn, and cassava. Starch occurs in two types: amylose and amylopectin. Amylose is a linear, helical chain, which is formed by the joining of glucose molecules via α(1→4) bonds by the enzyme, starch synthase. Amylopectin is formed by the branching of the amylose chain via α(1→4) bonds by the starch branching enzyme. Around 25% of the starch in plants are amylose while the rest is amylopectin. Starch is arranged into a semi-crystalline structure at the storage areas. It is found inside the granules called amyloplasts. Amylose and amylopectin are shown in figure 3.

Figure 3: Amylose and amylopectin

Carbohydrate Types

Sugar: Sugars are monosaccharides and disaccharides.

Starch: Starch is a polysaccharide.

Number of Monomers

Sugar: Monosaccharides are made up of a single monomer and disaccharides are made up of two monomers.

Starch: Starch is made up of 300 to 1,000 glucose molecules.

Complexity

Sugar: Sugars are less complex.

Starch: Starch is more complex than sugars.

Absorption

Sugar: Sugars are readily absorbed by the digestive tract of organisms.

Starch: Starch takes time to be absorbed.

Blood Glucose Level

Sugar: Sugars increase blood glucose level rapidly.

Starch: Starch increases blood glucose level slowly.

Conclusion

Sugar and starch are carbohydrates. Monosaccharides, disaccharides, and polysaccharides are three types of carbohydrate groups found in nature. Monosaccharides and disaccharides are water soluble substances. Since mono- and disaccharides are water soluble, they are sweet. Sweet carbohydrates are called sugars. Therefore, monosaccharides like glucose, fructose, and galactose as well as the disaccharides like sucrose, maltose, and lactose are sugars. Starch is a polysaccharide made up of joining a large number of glucose monomers together. Hence, the main difference between sugar and starch is their complexity of structure.

Reference:
1. Berg, Jeremy M. “Complex Carbohydrates Are Formed by Linkage of Monosaccharides.” Biochemistry. 5th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 18 May 2017. .
2. “Types of Sugar.” Monosaccharides and Disaccharides. N.p., n.d. Web. 18 May 2017. .

Image Courtesy:
1. By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Saccharose” (Public Domain) via Commons Wikimedia
3. “219 Three Important Polysaccharides-01” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia