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What Are Starch Grains?

author image Suzanne Allen
Suzanne Allen has been writing since 2004, with work published in "Eating for Longevity" and "Journal of Health Psychology." She is a certified group wellness instructor and personal trainer. Allen holds a Bachelor of Arts in communication and information sciences, a Bachelor of Arts in psychology and a Master of Arts in clinical psychology.
What Are Starch Grains?
White potatoes contain large starch grains that swell rapidly. Photo Credit: Jupiterimages/ Images

Starch grains are small granules found in the leaves, roots, stems, fruits and seeds of plants. These grains serve as energy reserves for plants. People may consume starch grains for energy, as starch grains are carbohydrates. Common foods containing starch grains or starch grain compounds include wheat, barley, rice, tapioca, oats, millet, sorghum, lentils, green peas, corn, potatoes and chick peas.

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The primary function of a starch grain is to provide carbohydrate energy to the plant. Transitory starch grains are housed in the leaves and stems of plants and stored temporarily for the plant’s immediate energy needs. Storage starches are starch grains located in the seeds, roots and fruits of the plant. The plant uses storage starch grains as a long-term energy reserve. Starch grains are turned into glucose for immediate fuel and converted into proteins, oils, DNA and other carbohydrates to meet the plant’s long-term needs. Similarly, when people consume starch grains, the grains are broken down into sugar for fuel or stored as fat.


Starch grains are composed of two types of glucose molecules, amylopectin and amylose. Amylopectin consists of highly-branched glucose molecules, while amylose is comprised of unbranched, linear glucose chains. The ratio of amylopectin and amylose in a starch grain determines the size and structure of grain. The size of the starch grain contributes to the swelling rate, the time it takes for a grain to absorb water. For example, tapioca starch grains are larger than rice starch grains, which cause the tapioca grains to swell at a rapid rate.

Glycemic Index

The glycemic index quantifies the rate at which carbohydrates increase blood sugar. The starch grains in instant rice and white potatoes swell quickly and convert rapidly into glucose, which cause blood sugar to increase swiftly. Thus, instant rice and potatoes are rated high on the glycemic index. The starch grains in lentils and other beans swell slowly and are digested at a gradual pace. These types of grains rank lower on the glycemic index. Generally, blood sugar increases rapidly when you consume starch grains with a quicker cook time and greater swelling ability.

Food and Non-Food Uses

Starch grains are used for a number of purposes. These grains are often added to foods to create a paste, sauce or gelatin texture. For example, starch grains are added to gum, pudding, yogurt, dressings, creams and certain candies. Additionally, starch grains are used to make pill capsules because starch easily disintegrates and allows absorption of the medication. Starch grains are also added to non-food products, such as spray starch, wallpaper, cosmetics, detergents, glues, paints and cardboard.

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