Starch is the major carbohydrate reserve in plant tubers and seed endosperm where it is found as granules, each typically containing several million amylopectin molecules accompanied by a much larger number of smaller amylose molecules. By far the largest source of starch is corn (maize) with other commonly used sources being wheat, potato, tapioca and rice. Amylopectin (without amylose) can be isolated from 'waxy' maize starch whereas amylose (without amylopectin) is best isolated after specifically hydrolyzing the amylopectin with pullulanase. Genetic modification of starch crops has recently led to the development of starches with improved and targeted functionality.

Starch is a white, odorless, tasteless, carbohydrate powder. It plays a vital role in the biochemistry of both plants and animals and has important commercial uses. In green plants starch is produced by photosynthesis; it is one of the chief forms in which plants store food. It is stored most abundantly in tubers (e.g., the white potato), roots (e.g., the sweet potato), seeds, and fruits; it appears in the form of grains that differ in size, shape, and markings in various plants. The plant source can usually be identified by microscopic examination of the starch grains. Starch obtained by animals from plants is stored in the animal body in the form of glycogen. Digestive processes in both plants and animals convert starch to glucose, a source of energy. Starch is one of the major nutrients in the human diet. Its presence in foods and other substances can be detected by the blue-black color produced when iodine solution is added to a sample of the material to be tested. By treatment with hot water, starch granules have been shown to consist of at least two components, known as amylopectin and amylose. Amylopectin is a branched glucose polymer; amylose is a linear glucose polymer. Commercially starch is prepared chiefly from corn and potatoes. Starch is widely used for sizing paper and textiles, for stiffening laundered fabrics, in the manufacture of food products, and in making dextrin. In addition to its other uses, cornstarch is a source of corn syrup, of which large quantities are used in making table syrup, preserves, ice cream, and other confections. Corn sugar (glucose) is also derived from cornstarch.

Starch is important because we eat it! Starch is found in potatoes, and in grains such as corn and wheat. Starch is made up of glucose repeat units.

In your body, special proteins called enzymes (which are also polymers, by the way) break starch down into glucose, so your body can burn it for energy. If you're eating a healthy diet, you get most of your energy from starch in this way. Because it is made of sugar molecules it is called a polysaccharide. It is very similar to cellulose. Starch has a few other uses other than food. It's used in pressing clothes to keep them from wrinkling. It's also used to make a foam packing. Starch is biodegradable, so starch foam packing is an environmentally-friendly alternative to styrofoam packing. But be careful!

Starch is versatile and cheap, and has many uses as thickener, water binder, emulsion stabilizer and gelling agent. Starch is often used as an inherent natural ingredient but it is also added for its functionality. It is naturally found tightly and radially packed into dehydrated granules (about one water per glucose) with origin-specific shape and size (maize, 2-30 µm; wheat, 1-45 µm; potato, 5-100 µm). The size distribution determines its swelling functionality with granules being generally either larger and lenticular (lens-like, A-starch) or smaller and spherical (B-starch) with less swelling power. Granules contain 'blocklets' of amylopectin containing both crystalline (~30%) and amorphous areas. As they absorb water, they swell, lose crystallinity and leach amylose. The higher the amylose content, the lower is the swelling power and the smaller is the gel strength for the same starch concentration. To a certain extent, however, a smaller swelling power due to high amylose content can be counteracted by a larger granule size. Although the properties of starch are naturally inconsistent, being dependent on the vagaries of agriculture, there are several suppliers of consistently uniform starches as functional ingredients.