1 Starch properties and products
1.1 What is starch?
Starch (the basic chemical formula of the starch molecule is (C6H10O5)n) is the storable form of energy produced by all green plants. Plants store starch in different organs (fruit, seeds, rhizomes and tubers) to prepare for the next growing season. Main crops with high starch content are potatoes, maize, sorghum, wheat, rye, triticale, barley, peas, rice and tapioca.
Starch, also called amylum, is a polysaccharide of glucose. Starch is stored in the plants as granules composed of amylose and amylopectin (amylose has a high tendency to retrograde and produce tough gels and strong films, whereas amylopectin, in an aqueous dispersion, is more stable and produces soft gels and weak films).
Starch molecules produced by each plant have specific structures and compositions (for instance the length of glucose chains or the amylase/amylopectin ratio), and the protein content of the storage organs may vary significantly. Therefore, starch can have different industrial uses depending on the agricultural raw material from which it was extracted.
1.2 The different technical stages of starch supply chains
The starch supply chain can be divided into three main technical stages.
Starch supply chains are composed of three main stages:
A starch supply chain is always based on agricultural production of plants with high starch content. The type of agricultural raw materials processed is different depending on the agricultural production potential of the geographical areas. Historically, potatoes were used in northern Europe, while maize and wheat were more commonly processed into starch in southern EU regions or nearby ports (where cereals are imported) and in North America. Rice and manioc are commonly used in Asia.
The second stage is starch manufacturing, which consists of extracting starch and separating it from the other molecules existing in the storage organ of the plants. Starch manufacturers extract native starch, but they also process it. They may therefore also produce modified or hydrolysed starches, which may constitute a very large range of starch products (further described in the next §). The extraction of starch from agricultural raw materials also produces industrial residues (effluents) and several by-products or co-products such as cellulose and proteins, etc. These products can be high-value products, such as gluten in the case of wheat, and can therefore greatly contribute to the viability of the starch processing units.
The third stage is undertaken by the end-user industries that process these starch products. These manufacturers belong to a large number of sectors such as the food sector, non-food sectors and animal feeding stuff.
These three stages may be more or less incorporated into the same companies.
1.3 Starch products
The starch molecule can be extracted and sold as such (native starch), but it can also undergo several processing operations in order to improve its proprieties and enlarge the range of its uses. Three main groups of starch products can be distinguished:
– Native starch is the starch chain extracted from raw material, in its original form. It can either be dried (powder) or not (liquid starch).
– Modified starches are starches modified by a chemical, physical or enzymatic process. They include:
Substituted starches: esters and ethers of starch, or cross-linked starches that are more or less resistant to gelatinisation.
Starch degradation or conversion made through oxidation, acid hydrolysis, dextrinisation or enzyme conversion etc. Starch degradation or conversion reduces starch viscosity and allows the use of starch with higher solids content. It increases water solubility, controls gel strength and can alter starch stability.
Physical modification: for instance, pregelatinisation of starch.
– Hydrolysed starches (Sweeteners): the starch chain can be broken into smaller glucose chains via hydrolysis. The more a starch chain is broken, the smaller the glucose chains are (this is measured by the Dextrose Equivalent (DE), which is the percentage of freed glucose molecules on a dry basis).
1.4 Interest of the various starch raw materials for manufacturers and end-users
Each agricultural raw material has specificities that impose the technological process applied for extracting starch, the range of starch products that can be processed and the final outlets.
– At the agricultural stage:it must be underlined that because starch potatoes have a high water content, it is not profitable to transport them. Moreover, they cannot be stored for a long period (potato starch concentration decreases during storage, particularly when subject to freezing temperatures in winter and higher temperatures in spring). However, potatoes have a significantly higher starch yield per hectare than cereals in the EU (see table below). This explains why historically in Europe starch was mainly produced from potatoes.
– At the processing stage:
The technology: industrial equipment and technology differ depending on the agricultural raw material. Switching from one raw material to another (especially from potatoes to cereals) requires major changes in equipment; therefore the choice of raw material is virtually irreversible.
The cost: the starch potato processing campaign is short, and the starch mills run only for a few months a year because potatoes cannot be stored. Starch potato plants produce a large quantity of residual water that the manufacturers have to dispose of. On the contrary, due to storage and transport factors, cereal starch manufacturers can run their plant all year long and produce fewer residues.
The products: it must be underlined that native starch properties differ according to the raw material. However, if starch is modified or hydrolysed, then the properties of the starch products no longer depend on the raw material from which it was extracted. In this case, manufacturers choose the most profitable raw material. For instance, wheat would be preferred to produce glucose syrup because the wheat starch chain is short and can be easily broken. In contrast, potato starch would be preferred in its native form because it has a longer starch chain, very regular starch granules and high purity.
The co-products: the co-products depend on the type of raw material used. For instance, starch wheat extraction produces gluten, which is a high value protein. Starch potato extraction also produces proteins, but in a smaller quantity, and they are sold at a low priceeven though it was recently discover that they may have promising properties.
– At the end-user stage: end-users prefer certain types of native starches depending on their uses. Compared to cereal starch, potato starch is considered as a high-quality native starch. Native starches produced from other tubers such as manioc starch have properties close to those of potato native starch. However, for several uses, native starches can be substituted for one other, even though they have distinct properties.
2 Uses of Starch products
The different uses of the starch products are presented in the table below.
Source: European Commission: http://ec.europa.eu/index_en.htm