The soya bean meal, the by-product of soya bean oil processing, is largely used for animal feed applications. It is also the starting material to make soya flours (with 50 % of protein content), soya protein concentrates (65 % of protein content) and soya bean protein isolates (more than 95 % of protein content). All these so-called soya protein products are used as ingredients in food applications.
Soya flour exists in 4 different formats :
- Enzyme-active full fat soya bean flour: mainly used in white bread for improving the colour of the bread crumb (due to the whitening effect of the oxydation of the carotenes resulting from the enzyme activity of the lipoxygenase enzyme)
- toasted full fat soya bean flour: mainly used in bakery applications such as cookies for reducing the breaking losses
- enzyme active defatted soyabean flour: also in bread applications
- toasted defatted soya bean flour: in bakery and meat applications
Soya protein concentrates
There are basically 3 ways to produce soya protein concentrates. They all use a different "protein immobilising principle". Indeed the trick is to make the protein insoluble during the extraction of the other water-soluble components (i.e. the oligosaccharides).
- One way of doing this is by heat treatment of the "white flakes" (the residue obtained after the oil extraction, which is normally the starting material for the production of soya protein concentrates and soya protein isolates). The name "white flakes" comes from the fact that while the oil is being removed by extraction, the carotenes are removed as well and the extracted residue gets a
typical white colour. During the heating of the white flakes, the tertiary and quaternary structures of the proteins are changed and they become water insoluble before the extraction process begins. This process is no longer used today because the protein has lost (irreversibly) most of its functional properties and because of the microbiological problems encountered in the process. - The second way is by using iso-electric extraction conditions, obtained by using acidified extraction water. This gives soya protein a pH with the lowest possible solubility characteristics. After the extraction the neutral pH can be restored by neutralisation and the protein regains its original solubility and functional
properties. This process results in the best tasting and most functional soya protein concentrates that have found applications in the preparations of fat emulsions for use in emulsified meat preparations for example. - The third process for making soya protein concentrates is the process that uses alcohol water mixtures for the extraction of the oligosaccharides.
This is the most popular process because it results in the blandest tasting and nutritionally most attractive soya protein concentrates. This process is based on the (irreversible) alcoholic denaturation of the protein.
Soya protein isolates
Soya protein isolates are pure soya protein that has been isolated from its original cellular matrix. The oligosaccharides (low molecular "sugars") as well as the polysaccharides (cell wall material) have been selectively removed from the meal after the fat extraction. These highly purified products are also used in meat applications for their water binding and jellifying properties.
Making soya protein isolates is a 3-step process : The starting material is again the "white flakes".
In the first stage, the flakes are slurried with water under alcaline conditions so that the protein (which become more soluble under these conditions of pH) as well as the oligosaccharides can go into solution. The polysaccharide containing insoluble residue is then removed by centrifugation.
In the second stage, the supernatant liquid of stage 1 containing the protein and the "sugars" in solution is acidified to the iso electric point of the protein (pH where their solubility is minimal). This results in the precipitation of the protein, which can be separated from the oligosaccharide containing supernatant.
In the third stage, the solubility of the precipitated proteins is reversibly restored and they are resolubilized by neutralising after redilution with fresh water.
Finally, the protein isolate solution is spray dried and packed in multilayer paper bags.
Soya protein isolates and concentrates in food
Isolates and concentrates can be considered as functional ingredients for the food industry and are normally sold in paper bags to this industry.
Further processing makes it possible to produce structured soya bean protein products such as textured vegetable protein (using extrusion technology) and even spun soya protein isolates have been developed which can simulate meat fibre structures. TVP is normally used as a meat "extender" and attempts have been made to completely replace the meat in spun soya protein-based meat "analogues".
Another possibility is making hydrolyzed soya protein: when low degrees of hydrolyzation are used, highly functional foaming agents can be obtained and when a high degree of hydrolyzation is used, typical HVP's (hydrolyzed vegetable protein) are obtained, which are used in soups and sauces as flavour enhancers.
