There are two types of starch, straight chain starch and branched chain starch.

Straight-chain starch contains a few hundred glucose units and branched-chain starch contains a few thousand glucose units. In the natural starch straight chain of 20% to 26%, it is soluble, the rest is branched chain starch. When tested with iodine solution, straight-chain starch liquid shows blue, while branched-chain starch becomes reddish-brown when in contact with iodine.

Starch is a nutrient stored in the plant body, stored in the seeds and tubers, all types of plants in the starch content is high, rice contains starch 62% to 86%, wheat contains starch 57% to 75%, corn contains starch 65% to 72%, potato contains starch more than 90%.

Starch is an important part of food, chewing rice, etc. feel some sweetness, this is because the saliva of the amylase enzyme starch hydrolyzed into a disaccharide - maltose. After the food enters the stomach and intestines, it can also be hydrolyzed by the salivary amylase secreted by the pancreas, and the glucose formed is absorbed by the wall of the small intestine and becomes a nutrient for the body's tissues.

Partial hydrolysis of branched-chain starch produces a mixture called dextrin. Dextrins are mainly used as food additives, glues, pastes, and in the manufacture (finishing) of paper and textiles.