SOY PROCESSING

Soy protein concentrates

There are basically 3 processes to produce soy 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" (i.e. the residue obtained after the oil extraction, which is normally the starting material for the production of soy protein concentrates and soy protein isolates). The name "white flakes"originates from the fact that while the oil is removed by extraction, the carotenes are removed as well and the extracted residue gets a typical white colour. In this heat denaturing process the tertiary and quaternary structure of the protein 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 to make soy protein concentrates is by using isoelectric extraction conditions. These conditions are obtained by using acidified extraction water. By doing so a pH is obtained whereby the soy protein has its lowest possible solubility characteristics. After the extraction the neutral pH can be restored by neutralisation and the protein regains its original solubility characteristics and functional properties. This process results in the best tasting and most functional soy 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 soy 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 most bland tasting and nutritionally most attractive soy protein concentrates. This process is based on the (irreversible) alcoholic denaturation of the protein.

Soy protein isolates

Soy protein isolates are pure soy protein which has been isolated from their 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 gelifying properties.

The process to make soy 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 alkaline 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 unsoluble residue is then removed by centrifugation.

In the second stage of the process the supernatant liquid of stage 1 containing the protein and the "sugars" in solution is acidified to the isoelectric point of the protein (pH whereby 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 of the process the solubility of the precipitated protein is reversibly restored and they are resolubilized by neutralising after redilution with fresh water.

Finally this protein isolate solution is spray dried and packed in multilayer paper bags.

Products produced from soy protein isolates and concentrates

All the products we have been discussing up to this point can be considered as functional ingredients for the food industry and are normally sold in paperbags to this industry.

Further processing makes it possible to produce structured soybean protein products such as texturized vegetable protein (in this case extrusion technology is used) and even spun soy protein isolates have been developed which can simulate meat fiber structures. TVP is normally used as a meat "extender" and attempts have been made for the complete replacement of the meat in spun soy protein based meat "analogs".

Another possibility is making hydrolyzed soy 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.

We must not forget the soy lecithin (a hydratable fraction of the raw soybean oil, composed of phospholipids) which is widely used as an emulsifier in the chocolate industry. The main component in soy lecithin is phosphatidyl choline.

SOY FOODS

Soy foods

We will now describe the world of soyfoods, of which soy drink is only one small example. Within the individually packed consumer goods we can distinguish between traditional (Chinese and Japanese) and Western style soyfoods.

Traditional Soy foods

Traditional soyfoods can be divided in non fermented and fermented products.

The main non fermented traditional soyfood in volume is soy drink itself (also known as tonyu, which is the Japanese word for soy drink). The second most important non fermented traditional soyfood in volume is tofu, which is better known as traditional soy cheese. Tofu is coagulated soy drink. There are essentially 3 types of coagulation agents available : the most popular one in China is nigari (which is produced as a by product in the process of sea salt production from sea water; it is the magnesium chloride rich portion of the minerals contained in sea water). Calcium salts such as calcium sulphate and or calcium chloride can also be used in tofu manufacturing. More recently new formats of tofu appeared on the market : silken tofu is lower in protein than traditional pressed tofu and consists of homogeneously coagulated soy drink whereby the coagulation is done in the packaging and using glucono delta lactone als a (slow speed) coagulant.

The most popular traditional fermented soyfoods are : tempeh, shoyu and miso. Tempeh is based on fermentation of soaked soybeans which are inoculated with a Rhizopus oligosporus strain (edible mould). It is "the Camenbert of the far east" and is very popular in Indonesia.

Shoyu is better known as "soy sauce", which is very popular in China and Japan. It is produced from a mixture of soybeans and wheat and is based on the use of the Aspergillus oryzae strain.

Miso is a fermented mixture of soybean with rice or barley and is also based on the use of the Aspergillus oryzae strain. Different products with different tastes and colours are obtained due to differences in fermentation temperature, time and different salt concentrations.

Apart from the tempeh fermentation, which only takes 2 days, all the other fermentation processes for traditional fermented soyfoods take months to come to an end. Delicate flavours are produced whereby a natural hydrolyzation process takes place. During this hydrolyzation process the larger molecules (protein, carbohydrates and fats) are broken down to smaller molecules.

Second generation soyfoods

Since a few decades new, "second generation" Western style soyfoods have been developed. Most of them are based on modern process technologies. Almost all of them are based on soy drink. In the literature one can find a detailed description of all the incremental improvements that have been made when beginning with the traditional soy drink process.

Before we go into all the details of soy drink processing it seems important to mention that soybeans are a very versatile raw material out of which an endless number of products can be produced for non food applications as well as for feed and food applications.

The soybean meal, which is the by-product of soybean oil processing is largely used for animal feed applications but is also the starting raw material in the process for making soy protein concentrates and soy protein isolates. It is also the starting material to make soy flours (with 50 % of protein content), soy protein concentrates (with 65 % of protein content) and soybean protein isolates (with more than 95 % of protein content). All these so called soy protein products are used as ingredients in food applications.

Soy flour exist in 4 different formats :
* enzyme active full fat soybean flour : mainly used in white bread for improving the colour of the bread crumb (due to the whitening effect of the oxidation of the carotenes resulting from the enzyme activity of the lipoxygenase enzyme)
* toasted full fat soybean flour : mainly used in bakery applications such as biscuits (cookies) for reducing the breaking losses
* enzyme active defatted soybean flour : also in bread applications
* toasted defatted soybean flour : in bakery and meat applications

Soy protein concentrates are products derived from soybean meal after extraction of the soybean oligosaccharides (raffinose and stachyose). They are used in meat applications for their emulsification properties.

Just to mention a few non food applications : soybean oil is used today in newspaper printing inks and soybean protein has been used for making biodegradable plastic materials in the past. New research activity has started in this field recently.

Soy processing in ALPRO

ALPRO has revolutionized these processes by developing a world exclusive process which has resulted in an unbeatable base drink with unprecedented sensorial quality.

We will now first discuss the traditional process.

* Whole beans are cleaned and soaked with water overnight.
* The soaking water which has not been taken up by the beans is withdrawn to drain.
* The swollen beans are then wet milled with fresh water to produce a fine slurry.
* Next step is to separate all the unsoluble material (cell wall debris, consisting of polysaccharides of the pectinic type) from the soluble material (protein, sugars and minerals). This is traditionally done with a cheese cloth. The unsoluble material (called okara) is removed and used for animal feed or in bread baking.
* The resulting soluble material is a milky emulsion better known as tonyu, which is the Japanese word for soy drink.

Traditional soy drink has a typical beany taste, which is accepted by the Chinese but which has never been accepted by the Western palate. The reason why the soy drink has this bitter and astringent taste, is the result of uncontrolled enzyme activity. The oxidation reactions catalysed by the lipoxygenase enzyme system, whereby oxygen reacts with the double bonds of the poly-unsaturated fatty acids are not under control in this process.

One of the first improvements which have been brought about to this traditional process was the simple principle of hot grinding. The technology was developed at the Cornell university in the late 60's by Hand et al. It consisted of milling the soaked beans with hot water (above 80ºC). By doing so the enzyme lipoxygenase which is rather heat labile is partly destroyed and the damage it can do is significantly limited.

In the 70's another improvement was brought about by researchers of the University of Illinois (Nelson, Wei and Steinberg) which consisted of blanching the beans before they were wet milled. The idea behind this process was to eliminate all lipoxygenase enzyme activity before the cells were damaged during wet milling. In this process whole beans were used and sodium bicarbonate was added to the blanch water to tenderize the beans. The slurry was subsequently high pressure homogenized and the inventors claimed a high yield. The problem was that they tried to keep all the components of the bean in the drink (whereby no okara was removed). The mouth feel of this "Illinois soy drink" was very chalky and sandy.

It was in the next decade, i.e. in the 80's that ALPRO developed it's own process for soy drink production. The basic process concept has been kept secret until today and has helped ALPRO to become the market leader in the European market.

Other dairy analog products have been developed from this basic soy drink since, such as yofu.

Yofu is a yoghurt like product made by fermentation of the soy drink with the classical yoghurt strains (Lactobacillus bulgaricus and Streptococcus thermophilus). It exists in different flavours as all kind of fruit preparations can be added after the fermentation process.

Ice dessert is another product which ALPRO has launched very recently.

An alternative for dairy cream has also been developed which contains 18 % of added soybean oil in which soybean lecithin has been used as an emulsifier.

It is worth mentioning that soy drink substitutes have been developed based on the use of "reconstituted soy drink" which are based on soy protein isolates. It is important to stress the fact that these "engineered soy drinks" are based on the principles of "mixing components together to obtain the end product" and of "adding back the nutrients" instead of "keeping the nutrients in the product". These soy protein isolate based soy drinks are normally composed of isolates with added refined soybean oil to which an emulsifier (mostly soya lecithin) is added; a stabilizer is also used to avoid creaming problems.

ALPRO soy drink is naturally produced from the soybeans and therefore it contains all the naturally present nutrients.

We will now explain the processing steps from the beans to the oil.

As soybeans contain only approximately 20 % of oil it is not economically attractive to produce the oil mechanically by using continuous presses. Only very small amounts of organic "virgin" soybean oil is produced that way, but it remains very expensive and is therefore not used very much. The only way to produce soybean oil from the beans in an economical way is by extraction. In order to extract the oil the beans are first cracked into small pieces (each bean is broken into 8 pieces on average) and after heating these pieces they are flaked between flaking rolls. By doing so all the cellular structures are damaged and the oil can now be extracted. The raw soybean oil is then hydrated whereby the soy lecithin is separated by centrifuges. This process is also called degumming. The degummed oil can then be further purified by deodorising under vacuum (whereby the volatile off flavours are removed) and by using adsorption techniques (removal of the non volatile off flavours and colouring compounds). Finally the so called refined soybean oil is obtained.

The refined soybean oil is mainly used as such in salads and inmayonnaises. It is normally further processed by winterisation (removal of the haze resulting from the presence of more saturated triglycerides) before filling. If the oil was not winterised the consumer would be confused when the oil would become opaque after cooling in winter. This "winter salad oil" remains clear when stored cold.

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The page was last updated Wednesday, 07-May-2008 23:57:11 GMT