What is water soluble in

Natural starch occurs as a reserve carbohydrate in tubers, roots, fruits, seeds and in the pulp of plants, for example in potatoes or grain seeds.
Soluble starch is a man-made product that is made by heating and swelling natural starch. The resulting starch paste is filtered off with alcohol. In the case of experimentation instructions, one must pay attention to whether starch is required which is soluble or natural starch like corn starch. The starch types have different properties.

Solubility in water as a physical property of natural starch can only be stated to a limited extent, as this depends heavily on the pretreatment. Natural starch is hardly soluble in water. Aqueous starch solutions are obtained with hot water, which solidify to a gel on cooling and form a starch paste. The production of wallpaper paste is based on this principle. In contrast to natural starch, the methyl cellulose in the wallpaper paste is pasted with cold water. Diluted, cold caustic soda and ammonia solution also cause the starch to swell.

In contrast to simple sugars, there is no reduction with Fehling's solution. With iodine-potassium iodide solution, however, a blue or purple color appears when heated. The strength verification serves to verify multiple sugars and starch.

A blue or purple coloration occurs when the strength is detected.

Natural starch is a mixture of two polysaccharides: amylose and amylopectin. Amylose can be thought of as a chain-like molecule in which many glucose rings are linked together. The amylose chains build up in a spiral helix with six glucose units per turn. Chains with up to 1400 glucose units are formed.

Amylose helical shape

Soluble starch mainly contains amylose (see> Cellulose). Corn and pea starch contain high levels of amylose. In amylopectin, the amylose chains are branched with one another. Such molecules are sometimes made up of up to a million atoms. There is a lot of amylopectin in potato, wheat or rice starch.


An amylopectin molecule is made up of amylose chains that also branch out.

Under the influence of dilute acids or enzymes such as amylase and maltase, these chains can be split open so that glucose is obtained again. During digestion, this process already takes place in the saliva. For this reason, a piece of white bread tastes sweet after a while if you chew on it for a long time.

The production of the reserve substance starch is an essential basis of the plant metabolism. During photosynthesis, plants generate starch under the influence of sunlight and with the help of the leaf-green pigment chlorophyll from the carbon dioxide in the air, which also creates oxygen. This process is known as assimilation:

Carbon dioxide + water Oxygen + starch ΔH = +2830 kJ / mole

The plant can convert the starch obtained into glucose and use it as an energy supplier. Reserve starch is deposited in the tubers of potatoes or in the seeds of cereal grains. The starch granules stored there contain amylopectin as a coating substance and amylose inside.
The natural starch is obtained from the flour of corn, potatoes, wheat or rice. The potatoes are grated to tear the cell walls and the starch granules are washed out. The proteins are separated off by slurrying, whereby the heavier starch grains sink to the bottom. The coarse cell components are separated off with a sieve, the starch granules settle in a milky suspension. They are dried at a maximum of 30 ° C and, when ground, make a fine flour.

To obtain the soluble starch, the cornstarch obtained is swollen at 90 ° C to form a starch paste. The starch paste is filtered off and the filtrate is separated off with alcohol. While amylopectin is responsible for the swelling, the main soluble starch that is obtained is amylose.
Starch is an important ingredient in high-carbohydrate foods. It is used as a binding and thickening agent for sauces. As a renewable raw material, starch is used to manufacture environmentally friendly plastics, pastes, adhesives, fillers, biodegradable detergents, dextrin, sorbitol, yeast, glucose or glucose syrup. You can use it to make biodegradable disposable tableware. Starch is used in the household as a stiffening agent for laundry, for example to stiffen shirt collars. In medicine, starch is a basis for ointments, suppositories and tablets. Starch is suitable as a binder for paints. It is also needed in beer production. Starch can even be used to make explosives based on starch nitrates.


Potatoes are not only suitable for eating, but also for biodegradable disposable dishes.

Further information
Carbohydrates in the organic dictionary
Cellulose as a polymer
Experiment: making a biodegradable film from starch