Seed oils

The most common seed oils

Seed oils are oils obtained from fruits or seeds of plants and trees other than the olive tree. These products are used first of all in the food sector, but they are also used in cosmetics (wheat germ, avocado oil ...), in the chemical industry (especially in the paint industry), and in the pharmaceutical industry (eg as a vehicle for some drugs, in the preparation of infusions for parenteral nutrition, etc.)

In-depth articles:

Flaxseed oil Grapeseed oil Coconut oil Palm and palm kernel oil Corn oil Sunflower seed oil Seeds of sesame seeds Wheat germ oil Jojoba oil Hempseed oil Castor oil Evening primrose seeds Avocado oil Soybean oil Rice oil Safflower oil Rape oil Peanut oil Walnut oil Macadamia oil Argan oil

In addition to the olive tree, numerous other plant species have seeds (70%) or fruits (30%) with an oil content that makes extraction convenient. Let's see the main ones;

PLANT	PART USED	PRODUCTS
Sunflower	Whole seed	Edible oil, margarine
Peanut	Whole seed	Edible oil, margarine
Safflower	Whole seed	Edible oil, margarine
Soy	Whole seed	Edible oil, margarine, baked goods
rape	Whole seed	Edible oil, margarine
Coconut	Fruit	Margarine, bakery products, cosmetics
Palm tree	Fruit (pulp)	Margarine, bakery products, cosmetics
Corn	Germ	Edible oil, margarine
Wheat	Germ	Dietary products, cosmetics
grapeseed	Seed	Edible oil, margarine

Because of the extensive production of herbaceous crops and greater productivity and yield, seed oils are less expensive than olive oil and, although with lower organoleptic characteristics, are suitable for raw consumption. Generally they are not suitable for frying, since the high temperature decomposes them quickly; however, there are exceptions, such as peanut oil and selected variatàs with a higher oleic acid content.

Oil extraction from seeds

The initial phases of the production process are preparatory, since all these foods derive from the soil and can therefore be contaminated by soil and leaves; consequently it is necessary to perform a preliminary washing and sieving. Once the clean seed is obtained, shelling and / or decortication and / or a depellicolation are performed, depending on the type of seed we are considering. Peanut, for example, must be shelled and pitted.

At this point, grinding and / or rolling is performed. For seeds with a high lipid content, a grinding is performed in order to reduce the seed into fragments, which must however be quite thick; in fact if the seeds are reduced to flour, then they tend to knead when they are pressed to obtain the oil. Lamination, on the other hand, is mainly carried out on seeds with a lower lipid content, which are reduced to very similar flakes to facilitate solvent entry and subsequent extraction.

The heating / conditioning phase follows. Generally these ground or rolled seeds are treated with wet steam, which makes them softer, facilitating the extraction of the oil and increasing its yield.

At this point the process is divided.

If we have a seed with a high lipid content we perform an initial pressing, with continuous presses similar to those seen for olive oil. From this process a crude oil is obtained which must be rectified; all seed oils must be rectified, since the simple extraction leads to product defects: either because it has too strong colors (palm oil is brown), or because it has unpleasant flavors or adores, or for high acidity.

The panel that remains from this pressing, ie the solid material, is crushed and subjected to a solvent extraction, as it still contains a minimum percentage of non-extractable oil by simple pressing. The same applies to seeds that have a low lipid concentration or are very small, such as cotton, for which it is impossible to press. Similarly to what happens for pomace, in these cases it then passes directly to solvent extraction. The most widely used solvent is hexane, through a process similar to that seen for pomace. Hexane dissolves the lipid component, and the product obtained is subjected to distillation in order to separate the solvent and reuse it for the extraction of seed oil. The product obtained is obviously a crude oil which must then be rectified.

Solvent extraction can also be performed in continuous or discontinuous systems.

In discontinuous ones the maceration of the material in hexane is used, in those it continues the countercurrent passage of the seeds and the hexane.