Soya is a herbaceous annual plant with an aspect similar to the one of the black bean.
The plant with numerous branching supporting dense foliage can reach a height of 0.3 to 2 m following varieties.
The alternate leaves are 5 to 15 cm long. The bean is a pod, green before maturity and yellow to black at maturity.
The pods are self-opening at maturity and have a length of 3 to 11 cm; they contain 1 to 4 beans (usually 2 or 3).
The beans are spherical with a diameter of 5 to 10 mm, with a colour from yellowish to black brown flwg. varieties; some have even beans of oval and flattened shape. The varieties with yellow beans are the richest in oil.
Soya may be cultivated in every tropical or sub tropical country and even in most of the tempered climates.
Soya has been cultivated since very old times in China and in Manchuria, where it constitutes the basis of human food, as in Japan.

Since early of 20th. century, soya cultivation has grown considerably in USA.

The major factors to its cultivation expansion are :

• the cultivation of this plant is easily mechanically done for sowing, cultivation and harvesting;
  
• the seeds can be stored easily and without much damage;
  
• it is a very rich source of proteins;
  
• many varieties exist and can accommodate many soils and climates.

It is one of the least requiring plants in hot countries; it just needs a lot of water when reaching maturity and its optimal temperature is around 25°C. The most important factor during its maturity is the lighting duration.
Today a manual harvesting followed by flail threshing is exceptional.
Mechanisation has been largely developed and yields reach 2500 kg per hectare.

End uses

Next to its use as an oil seed, soybean has been also used :

• after meal production, it is incorporated in baby foods, biscuits, flour meal, bread, ...
  
• as a meat replacer : thanks to its proteins similar to the meat proteins, it can replace meat when missing or undesired
  
• after soaking of the beans, a milk is obtained which can be used for baby food
  
• in preparation of some cheeses, milk cream, ...
  
• after deoiling, the meal is very rich in protein (45 to 50% according to prior dehulling or not) and is highly appreciated in animal feed. It can also be used as organic fertiliser.

Composition

Soybean has the following composition :

• 9.5 to 14% of moisture
  
• 18 to 22% of oil content
  
• 39 to 47% of proteins
  
• 3 to 20% of carbon hydrate
  
• 4 to 8% of fibres
  
• 3 to 6% of ashes

The process

Precleaning
Precleaning is done in high-capacity machines with screens and aspiration channels to remove undesirable by-products from the harvest, such as stems, straw, stalks, chaff, stones, loose hulls or other cereals and seeds.

Seed drying
Beans are ideally dried to 10-10.5%
Minimum 1% drying.
Bean temperature: max.65°c
Bean storage(tempering) after drying detaches hulls and equalizes moisture between beans.

Cracking
Cracking of the beans is done to reduce the particle size.
Set up of the rolls is extremely important:
-Maximizing slicing action
-Minimizing smashing action creating fines and wear
-Mills with corrugated rolls are used

Dehulling
Dehulling is necessary when producing Hi-Pro meal with following characteristics after extraction :

Proteins : 48-50% (min 47.5%)
Lipids : approx 1%
Fibre : max 3,5%
Moisture : 12-12.5%

Hi-pro meal is the most recommanded for poultry feed.

Conditioning
Heating up with enough residence time to increase the plasticity of the cracks, and make it possible to flake them.

Vertical stack cookers and horizontal, rotary cookers are both used.

Flaking
The seeds must then be flaked to break down the walls of the oil containing cells, making it possible for the solvent to penetrate the cells and extract the oil.

The main points to watch are the steadiness of the feed to the unit, and the condition of the cylinder surfaces.

Expanding
As an option, the flakes can be expanded.

This is helping the extractibility and the desolventising of the flakes.

This apparatus is very often installed in the purpose of capacity increase of an existing plant.

Solvent Extraction

Flakes specifications:

• In the oil < 100 ppm solvent
  
• In the air vented <10gr/m³ of air
  
• In the waste water < 20ppm.

Degumming
Soybean oil contains over 2% phosphatides.They are precipit- ated by water addition and separated in the degumming process.

Wet gums can be added back to the meal in the DT, or dried to produce lecithin.

Neutralising
These unit operations reduces free fatty acids to below 0.08% and phosphorus to below 3 mg/kg. Iron and copper concentrations are reduced to below the detection limit. Coloured compounds (chlorophylloids, carotenoids) are not affected significantly, altough chlorophylloids can be reduced by 30-70% of the original concentration under certain process conditions. The concentration of sulfur compounds is reduced slightly.

Bleaching
The neutralized oil is usually golden yellow, which is not yet suitable for food purposes.It is necessary to bleach the oil so as to remove the various pigments not removed by neutralization. This is done with adsorbents in the form of bleaching earth or activated charcoal.
Soybean oil is bleached at a maximum temperature of 100°C- 105°C. The bleaching earth must be used in concentrations of 0.3-0.5% of the oil weight in chemical refining.

Deodorising
For soybean oil in chemical refining we can present some typical operating parameters:

The improved deodorisation technology has led to a perfect overall refined oil quality:

• Low residual FFA and high oxidative stability
  
• Light color, bland odor and taste
  
• Low trans and polymeric triglyceride content
  

Furthermore we are perfectly in control of the removal of minor components:

• Adjustable process conditions
• Limited thermal/oxidative degradation.
  

A special Dual Temp^® Deodoriser is also available with:

• Low temperature-long time for mild deodorising and moderate stripping and thermolytic/hydrolytic breakdown reactions
  
• High temperature-short time for stripping and heat bleaching and for controlled removal/retention of valuable minor components

Hydrogenation
Oil quality required for the hydrogenation:

• change the overall melting profile (usually to smoothen the solid fat content) or the melting point of the mixture (usually a decrease)
  
• improve the compatibility of the different triglycerides in the solid state
  
• improve the plasticity of the resulting solid by changing the (re)crystallisation properties
  
• combine the properties of mixed oils and fats
  

Fractionation
Dry fractionation is the simplest and cheapest modification process, as it is not the source of oil losses, any more than it requires supplementary post-treatment of the finished products.

Especially in today’s fast changing market, fractionation offers some serious advantages over hydrogenation and interesterification.

The very low operating costs as well as the zero oil loss and full reversibility of the process make it most attractive.


Soybean oil composition

[Top] [Home page]

15/03/2005