What is starch?
Starch is a carbohydrate extracted from agricultural raw materials which is widely present in literally thousands of everyday food and non-food applications. It is the most important carbohydrate in the human diet. Because it is renewable and biodegradable it is also a perfect raw material as a substitute for fossil-fuel components in numerous chemical applications such as plastics, detergents, glues etc. For more on the food, feed and industrial uses click here. The starch molecule consists of a large number of glucose units joined by glycosidic bonds. It is produced by all vegetables as an energy store. In Europe it is extracted almost exclusively from potatoes, wheat and maize.
The starch categories
Pure starch can then be modified by a chemical, physical or enzymatic process to create ‘modified starches’, each offering differing characteristics and used widely in the food, paper, textile, oil, adhesives, fermentation and pharmaceutical industries. More on modified starches
Starch in 3 minutes
Extraction and processing
From plant to powder
Starch is the glucide reserve of plants. In Europe it is found in maize, wheat and potato from which it is extracted, as well as in many other plants: rice, barley, vegetables, manioc, sweet potato.
The formation of starch in plants is through the process of photosynthesis. This physiological mechanism makes it possible for the plants to produce and store the glucose (elementary sugar) which is necessary for their growth and reproduction.
Initially, the plant assimilates the carbon from the atmosphere and transforms it into glucose, the basic molecule. This is then used for the synthesis of the starch polymers associated with pure glucose.
Like the image of a “pearl necklace”, each plant organises and structures its macromolecules of glucose in a different way, the number of glucose units which can vary from 100 to 20,000 in each polymer. In plants, starch appears as small granules, insoluble in cold water, the size (between 3 and 100 microns) and form vary according to the origin.
The starch industry separates the components of the plant: starch, protein, cellulose envelope, soluble fractions and in the case of maize, the germ from which oil will be extracted. This first phase utilises a series of simple stages of physical separation of the components: crushing, sifting, centrifuging, etc… However the methods of manufacture are specific to each plant and the industrial tools are normally dedicated to a raw material (maize, wheat or potato in Europe). In the second stage, the starch which has been extracted in its purest form, will be used as it is after drying (this is called “native starch”) or it will be further processed, undergoing various transformations aiming either at modifying its performance (“modified starch”) or to obtain sweeteners through the process of hydrolisis.
At the end of the process the starch and derived products are delivered to customer industries in the form of powder (with an appearance similar to that of flour) or of syrups.
Solving to suit
The properties of starches are well-known, however knowledge continues to progress in the understanding of the physicochemical bases of their application.To bind, thicken, texture, stabilise and gel are some of the traditional functions of starch. Native starches are perfectly suited to a wide variety of applications, food or non-food, where their properties remain irreplaceable. Very early however, it appeared necessary, in some cases, to improve the performance of the starch and to respond to the needs of customers, giving other improved functionality or behaviour: solubility with cold water, more stable viscosity with the variations of temperature, hot fluidity, better stability… The first modified starch dates from the 19th century and other modified starches were since then developed, often in partnership with customer industries, which sought to make starches compatible with their industrial processes. In the food area, the principal modifications aim at adapting the starch to the technological constraints resulting for example from cooking, freezing/thawing, canning or sterilisation and to make them compatible with a modern food (microwavable, instant preparations, ultra high temperatures and so on). One of the objectives common to the majority of these transformations is to limit the natural tendency of starch to be retrogress. During the cooking of soup for example, the native starch is hydrated in contact with water. The starch granules expand and the “viscosity” of the solution increases giving it a particular texture.
The various modifications of starch make it possible to obtain:
- easier food preparation
- better conservation of food
- better stability of food even when heated under severe conditions (preserves for example, to ensure their sterility)
Main technical modifications:
- Cross Linking is the creation of bridges between the starch chains with specific connections. This process makes it possible to maintain inflated granules and to decrease the loss of viscosity.
Substitution gives stabilisation property to starch, mainly during cycles of freezing and thawing. This is thanks to molecules which ensure the repulsion between the starch chains, these cannot recombine. The minimisation of the starch retrogradation is thus ensured.
Starch sweeteners / Glucose syrups
A sweet choice of possibilities
The starch molecule consists of a large number of glucose units. Glucose has been essential in the food industry since the 19th century, when Europeans sought to substitute products for cane sugar which was in short supply. The industrial process of starch hydrolysis first appeared in 1811 when German scientist KIRCHOFF discovered that it was possible to give a sweetened character to starch by heating with water and sulphuric acid. Later during the 1960’s enzymatic technologies began to be used in the industry for starch hydrolysis: this interest in enzymes for use in the starch industry has increased significantly. Starch sweeteners meet the demand of sweetening mixtures and bring additional functionality to many sectors (beverages, confectionery, dairy products…), contributing to the texture, colour stability and flavour of the final product, while also remaining economic. For example, glucose syrups are used in confectionery mainly for their anti-crystallizing role, while in brewing they are especially used for their sweetening power. Glucose syrups can adapt, as with the starch from which they result, into a considerable variety of products, each developing specific properties. The hydrolysis -by the important choice of the enzymatic transformation- allows the production of very broad ranges of products with a wide spread of sweetening capacity, texture and taste.
Sugars/Sweeteners produced by the starch industry include:
Fructose-glucose syrup (term used as a legal designation for labelling purposes)* is a glucose syrup which contains more than 50% fructose on dry matter basis. The most common type contains 55% fructose, although production within Europe is minimal.
High fructose corn syrup (HFCS)(term not used in the EU but only in the US and in some other regions in the world for a GFS or FGS). It is most commonly 42% or 55% fructose containing syrup. The use of HFCS developed more in the US than in the EU because in Europe since 1970 a production quota is in place for glucose syrups including more than 10% fructose, in the framework of the Common Agricultural Policy.
Dextrose (term used as a legal designation for labelling purposes)* is a purified and crystallised glucose.
Fructose (term used as a legal designation for labelling purposes)* is a purified and crystallised fructose.
Maltodextrins (they are not defined in the “EU sugars directive”). An EU starch industry definition exists published in Starch 43,6,247 (1991) that describes them as nutritive saccharides consisting of glucose and its oligomers and polymers, with a dextrose equivalent (DE) of less than 20. They are prepared as white powders or concentrated solutions by the partial hydrolysis of gelatinized food starches.
Polyols are low caloric alternative sweeteners. Some of them are produced using starch as a raw material. Those which use starch as a raw material are:
Sorbitol is purified sorbitol obtained by reduction (hydrogenation) of glucose. Sorbitol is found in fruits such as apples or pears.
Sorbitol syrup is formed by reduction of glucose syrup and composed of sorbitol, mannitol and hydrogenated saccharides.
Maltitol and maltitol syrup. Likewise, while maltitol is purified amtitol (reduced matose), maltitol syrup is mainly composed of maltitol with sorbitol and hydrogenated oligo- and polysaccharides.
Polyglycitol syrup consists mainly of maltitol and sorbitol and lesser amounts of hydrogenated oligo- and polysaccharides and maltrotriitol. It is manufactured by the hydrogenation of a mixture of starch hydrolysates consisting of glucose, maltose and higher glucose oligomers. Similar to the catalytic hydrogenation process used for the manfufacture of maltitol syrup.
Mannitol is purified mannitol (reduced mannose) produced by hydrogenation of sugar solutions containing glucose and/or fructose.
Erythritol is purified (reduced erythrose, a 4-carbon sugar). It is obtained by fermentation starting from glucose. It is found in fruits such as pears, melons and grapes, as well as foods such as mushrooms and fermentation-derived foods such as wine, soy sauce and cheese.
Colouring caramels are liquids or solids with a brown dark colour, water soluble, obtained by a controlled action of heat on food sugars. The principal use is the colouring of foodstuffs. They improve the appearance of products, giving some colour and eliminating the colour variations. The use of colouring caramel began around 1840 in a broad range of products, such as alcoholic drinks (beers, liquors, brandies, rum, whisky), carbonated beverages, (colas…), soups and sauces, vinegars and condiments, preserves, dairy ice creams, bakery products, biscuit factory and confectionery and pharmaceutical products. Aromatic caramels are liquids or solids with a brown dark colour, water soluble, obtained by a controlled action of heat on food sugars. The principal use is the colouring of foodstuffs. They improve the appearance of products, giving some colour and eliminating the colour variations. The use of colouring caramel began around 1840 in a broad range of products, such as alcoholic drinks (beers, liquors, brandies, rum, whisky), carbonated beverages, (colas…), soups and sauces, vinegars and condiments, preserves, dairy ice creams, bakery products, biscuit factory and confectionery and pharmaceutical products.
*For the terms mentioned above as being used as legal designation, the so-called EU “sugars directive” (Directive 2001/111/EC) provides a definition and specifications.
Gluten feeding people and animals
The job of the starch manufacturer is to extract starch from cereals or from potato in its purest form. Among the other components of cereals and potato, all of importance and use, proteins are of particular interest as both nutritional and functional additions for animal feed as well as for human consumption.
According to the raw materials, proteins have specific qualities and uses:
Maize proteins are developed in animal nutrition in 2 forms:
purified maize protein or maize gluten
with draffs as maize gluten feed
wheat gluten (wheat protein purified) is used:
- or approximately 20% in animal nutrition
and for 80% in human nutrition
proteins of potato are developed in animal nutrition in 2 forms:
- purified proteins
- pulps enriched in proteins
Wheat gluten and human consumption:
Rehydrated gently, vital wheat gluten has the capacity to form a continuous extensible and airtight elastic network. It is the only protein with this property, which is called visco-elasticity.
If a flour does not contain enough gluten, the bread breaks down, has little volume, and its crumb is irregular. Millers use either wheat, rich in proteins, or directly gluten in order to improve the quality of baking of flour.
Thanks to its properties of visco-elasticity and binding, gluten also improves resistance in puff and frozen pastries. It ensures good handling, and also cohesion of meat preparations . Wheat proteins offer high nutritional value , and can be used either as a basic ingredient, or combined with other vegetable proteins. A pure and concentrated source of proteins, they form a perfect substrate for hydrolysis in the preparation of soya sauces and vegetable protein hydrolysates.
90% of gluten is used in applications which traditionally employed wheat flour.
Proteins and animal nutrition:
The proteins coming from the starch industry are purified and standardised proteins. They are vegetable proteins with each one having particular characteristics. Thus they are useful, in addition to their nutritional properties, for particular applications within animal nutrition.
Thanks to their good nutritional balance resulting from an excellent distribution of the amino acids, potato proteins are part of the composition of high added value food, intended for calves ( milk substitute), or for piglets.
The specific richness of maize proteins in yellow pigments makes them highly interesting in certain food products (influence on the colour of eggs). They are also increasingly used in dry food for dogs and cats.
Wheat gluten is used both for its nutritional properties (higher digestibility) and as a binder, for the cohesion which it gives particularly in aquatic feed or in meat analogues for pets food.
Hydrolysed protein is used as the first choice source of protein in food for calves and piglets.