Oilseeds conservation

Introduction

For efficient extraction, should be retained oilseeds against some biological and physicochemical factors that may affect the quality and quantity of oil extracted.

Factors altering

The seeds are the subject of several changes:

• altered by micro-organisms in the presence of moisture;
• alteration by the action of enzymes;
• alteration by the action of air

Microorganisms

a) Mold:

Mold can develop most often in the presence of air and preferably in the hot and humid atmospheres.

Their action is seen as much more than the humidity of the environment is higher but for some molds, it is already below 20% relative humidity, which corresponds to a moisture content of 3 to 4%.

Some say toxigenic fungi can secrete mycotoxins as the case of Aspergillus flavus secret that aflatoxin B1 has a carcinogenic effect daunting. This secretion does not generally in the oil during extraction thereof by hexane and is therefore in the cake.

b) The yeasts:

Their development occurs over a relative humidity above 88% (ie a water content of 19.5%) mainly on carbohydrates present in the seeds.

c) Bacteria:

They can grow at a_w>0.9, but generally the extracted oils are stable at the time of microbiological conditions intrinsic oils do not promote microbial growth.

Alteration by enzymes

The enzymes can trigger the hydrolysis of triglycerides, resulting in an additional loss in oil: the party will be driven subsequently hydrolysed with soap formed during treatment with soda.

Alteration by air

The unsaturated components are particularly sensitive to oxidation even at ordinary temperatures and more so when the temperature is higher. It is formed hydroxy derivatives and their reactions, added to others, contributing to a rise in temperature within the silo.

The air acts to assist the development of aerobic microorganisms and provides water for the hydrolysis of lipids in the seed.

Finally, in addition to its oxidizing action, the air allows the proliferation of insects.

Temperature and humidity

We have seen that these factors affect the growth of microorganisms and the interactions within the seed. Generally, water content not to exceed suitable for conservation of seeds is 4 to 5%.

Insects

Insects are one of the biggest scourges that affect the seeds at various stages from harvesting to crushing, they attack the seeds for food and reduce the dust and broken kernels.

Criteria and methods of conservation

Knowing the causes and factors of weathering, one can compensate for the alteration of seeds using some technological operations detailed below.

Screening before treatment

If we can not avoid broken seeds during the various manipulations, it is necessary to sieve to remove broken and Farinette because they have a much higher acidity than the whole seed which increases losses during saponification and requires larger quantities of soda ash to neutralize.

Drying

Drying is to lower the maximum moisture content, possibly to the limit where microorganisms can grow. One technique is to send sound to the mass of seeds, introduced within the silo, a stream of air resulting in a drying training.

Conservation in confined space

The seeds eventually subdued and properly dried, are placed in hermetically sealed silos. As long as the air remains in the interstitial spaces, the seeds continue to absorb oxygen to convert CO₂, and gradually disappear microorganisms and insects.

Conservation in CO₂

This process involves replacing all the air of the silo by which carbon dioxide is injected in sufficient quantity. In these conditions all the insects disappear along with all the phenomena of chemical and biological transformation.

Note however that the seed loses its vitality and its germination decreases significantly when the storage is for a long time.

The amount of CO₂ needed for a batch of seeds determined, depends on the nature of these seeds, for the following reasons:

• it depends on the intergranular space, which varies depending on size of seeds.
• it depends on the oil content of seeds, this oil with a high absorbency of CO₂.
• it is a function of water content in which CO₂ is partially soluble.
• it is a function of temperature: the solubility of CO₂ is inversely proportional to the increase of temperature.

Process of cold

The principle of the process is as follows: It breathes through the silo, a current of air. It is saturated with water vapor, and then leaving the silo, it is cooled by a refrigerating machine to a temperature where water vapor condenses driven.

This process reduces the moisture in the air storage, and therefore limit the microbial growth and especially mold capable of compromising the safety of seeds.

Materials used for the construction of silos

Concrete is more or less porous, it must be smeared with a coating that makes it impervious walls. The coating should have no effect on seed quality in contact. The best solution is to use steel silos, there are different models. The outer surface is protected against weather by a suitable protective coating. It may also, for the same use of wooden silos.