Knowledge Base Starch
Starch (amylum) is a complex carbohydrate, a polysaccharide to be precise, that is made up of a large number of linked glucose molecules (so-called monosaccharides).
Plants store energy in a variety of forms: sugar beet and sugar cane, for example, store energy in the form of disaccharides (glucose-fructose molecules), while corn, potato, wheat and tapioca store it in the form of starches (glucose molecules).
Starch is an important means of storing glucose and therefore one of the most important means of storing energy for land plants and green algae.
Starch is generally stored in plant cells in the form of organized grains of various sizes and shapes, depending on the species of plant.
Starch is made up of
- 10-30 % amylose, which is unbranched chains of linked glucose molecules in a helical structure
- 70-90 % amylopectins which, due to multiple linkages between the glucose molecules, have a more complex, branched structure
How is starch produced?
In our latitudes, starch is mainly obtained from corn, wheat or potatoes. Other important sources of starch are rice and manioc (tapioca).
The principle of extracting starch from plants can be explained in simple terms as follows:
- The parts of plants containing the starch are chopped into such small pieces that cells containing starch are also destroyed.
- The starch is then “rinsed” out of the cells before being separated out by means of filtration and centrifugal processes.
- This also includes the separation out of cellular structures. The starch is finally dried.
Native starch is obtained in the form of a white powder.
The properties of starch
The most important property of starch is its ability to gelatinize. When a mixture of starch and water is heated, the starch is able to physically bind an amount of water equivalent to many times its own weight. The starch swells and gelatinizes. The starch paste has different characteristics depending on its source plant (potato, wheat, corn, etc.). Starch paste not only forms coagulated gluten but is also used as the basis for all sorts of bread and baked products. At lower temperatures the previously gelatinized starch slowly reforms.
This effect is known as retrogradation and is due to the amylose contained in the starch which, due to its chemical structure, is not able to bind water as effectively as amylopectin. Retrogradation is the process which takes place when bread goes stale.
What are starch and starch-based products used for?
- Native starch is a powder obtained from plants containing starch. It is used as a thickening agent and a stabilizer. Good examples of this include custard, desserts, sauces and many forms of instant foods.
Modified starches are obtained from native starches as a result of physical, enzymatic or chemical processing methods. Wet and dry chemical processes, drum drying and extrusion methods are all used. The properties of native starch such as its freeze-thaw stability, acid or alkali resistance or even its shear stability can be changed by means of these processes. Depending on the raw materials used starch is used for different applications. Native and modified starches can, for example, be used as ingredients in the production of foodstuffs, but also for technical purposes (in the textile, paper, cosmetic, pharmaceutical and construction industries).
- Starch saccharification products are formed by separating starch into its constituent sugar components. In this way, sugar can be obtained not only from sugar beet but also from starch-rich plants such as corn or potatoes. Starch saccharification products are largely used for sweetening carbonated soft drinks, ice cream, jams, confectionary, etc.
Starch saccharification products include:
- Maltodextrins are unlike native starch in that they are easily soluble in water and do not retrograde. Maltodextrins are used to add calories to diet and tonic products or as carrier substances for dry aromas. They also thicken instant meals such as soups and powdered drinks to make them more filling without appearing thickened.
- Glucose syrups (including starch syrup, isoglucose, corn syrup, corn sugar, etc.) have a higher degree of saccharification than maltodextrin and are therefore more effective sweeteners. If glucose syrups are subjected to an isomerization process, some of the glucose they contain is converted into fructose to create glucose-fructose syrups (isoglucose). These syrups have greater sweetening strength due to the higher proportion of fructose, nearly on a par with crystallized sugar, and are therefore used in carbonated soft drinks and confectionary.
- Glucose, also known as dextrose, is a monosaccharide that is produced by crystallizing highly sweetened glucose syrups.
What nutritional role does starch play?
In addition to proteins and fats, carbohydrates are the most important sources of human nutrition and energy. 1g of carbohydrate (such as starch) provides as much energy as 1 g of protein, namely 4 kcal (17 kJ).
In comparison to carbohydrates, the energy content of 1 g of fat is 9 kcal (37 kJ), meaning that fats provide considerably more energy than either proteins or carbohydrates. Carbohydrates consumed as food are broken down or converted in the human body into glucose. Only unbound glucose molecules can be absorbed into the body through the wall of the intestines.
Glucose is generally preferred by the body as a source of energy and it is particularly important for supplying the brain, kidneys and red blood cells with energy.
According to the D-A-CH recommendations on nutrition published by the German (DGE), Austrian (ÖGE) and Swiss (SGE/SVE) nutritional agencies, 50% - 55% of our daily energy requirements should be provided by carbohydrates.
The main emphasis here should be placed on complex carbohydrates such as starch. These complex carbohydrates, which are particularly common in potatoes and cereal products, are absorbed by the body more slowly and therefore have a positive effect on the rate at which insulin is secreted and blood sugar concentrations rise.
It is also interesting to note that hard-to-digest starches also exist. These so-called resistant starches are therefore classified as roughage – substances which cannot be broken down by human enzymes, but which are partially broken down by bacteria in the bowels. Roughage plays a number of important roles in the digestive tract and also has positive effects on the metabolism.