Cotton Seed

Hundreds of De Smet plants are processing cotton.


Origin

Cotton belongs to the Gossypium sort.

We find :
- the Asian group (Gossypium Negraceum et Gossypium Arboreum) which gives a cotton with short fibres (14-25 mm). They are cultivated in Persia, Asia Minor, Greece and Turkey.
- the American group (Gossypium Barbadense, Gossypium Peruvianum, Gossypium Hirsutum) which gives the cotton with long fibres. They are cultivated in the USA, Central Africa, Egypt, Republic of Congo, Central America, India and Turkestan.

Cotton is an annual herbaceous type of which the fruit gives a down, which constitutes the cotton itself. The stem is ramose with a height of 0.6 to 2 m (sometimes up to 6 m). The leaves are more or less large, with a petiole with 3 to 5 triangular lobes. Flowers, growing at axilla of the leave supported by long peduncles, are of ivory, red or yellow colour. The pods or fruits, hard at maturity, have the shape of a capsule which self opens at maturity and contain 3 to 7 oily seeds on which are adhering some white silks and a down (lint) of grey white or green colour.

The cultures yield 4000 to 1000 kg of seeds per hectare. The harvest is done in several passes according to maturity, and manually, with scissors or mechanically. The capsules are put for a few days to dry and the ginning machine then separates the seed used in the oil industry from the fibres, which are pressed in big balls by hydraulic press.

The cotton fibre from ginning represents about 30-35% of the total seed weight and is used for textiles, flannels, padding or cotton wool, etc...

The seed itself without long fibres is still covered by short fibres called ‘lints’ adhering to the shell. They are removed in delinting, usually performed in two successive cuts.


Composition

An undelinted seed composition is about :

• 8-10% of lint
• 18-22% of oil
  
• 30-35% of meal
  
• 30-35% of hulls

Crude cotton oil
It is a semi-siccative oil and its main characteristics are :

• 46-54% of linoleic acid
  
• 18-24% of oleic acid
  
• 0.8-1% of palmitoleic acid
  
• 22-26% of palmitic acid
  
• 1-3% of stearic acid
  
• 0.2-0.4 of arachidic acid
  
• 0.2% of behenic acid
  
• 0.5-1% of myristic acid
  
• Iodine Value : 100-115
  
• saponification value : 192-200
  
• melting point : -2/+2°C
  
• titer : 38-32°C
  
• unsaponifiables : 1.5%

Process

Before extraction, the cottonseed is more or less decorticated.
80% of lint are usually removed and serve in industries of carpets and of lower quality textiles and after chemical transformation, in industries of cellulose, collodion, cellulose acetate, ...
Decortication removes about 80% of total remaining hulls and lint weight.
To give an idea, 100 kg of cotton (with 20% of oil, 10% of lint and 35% of hulls) give :
- 8 kg of lint
- 28 kg of hulls with 1.6 kg of lint
- 62 kg of decorticated seeds with 32% of oil and 56.5% of meal.

The above values vary according to varieties.

Delinting and decorticating the cotton are jobs on their own.
Pre-pressing may treat decorticated cottonseeds after a preparation, which includes corrugated rolls, flaking and cooking (with increase of moisture to 18% before reduction to 6-8%).
The cake is then cracked, cooked and flaked before solvent extraction.

Direct solvent extraction is possible to extract the oil from partially decorticated seeds after preparation by cracking, cooking and flaking followed by a crisping by quick cooling.
Today, expanding which gives a better extractability in direct solvent extraction preferably does seed preparation.

Crude cotton oil is very sensitive and its colour is normally high due to gossypol and its taste is very specific.

Crude cotton oil has a red colour, more or less strong, not only according to the variety and the seed conditions but also to the process used for its production. The seed does contain a specific colour pigment, gossypol, which combines more or less completely with proteins especially during the cooking and moistening steps. The rest of unbound gossypol is called ‘free gossypol’ and is distributed between oil and meal.

Neutralising with caustic soda requires a lot of excess and normally a re-refining step to eliminate the colour. Of course, it results in heavy neutral oil losses by saponification.

Miscella refining is particularly recommended on this kind of oil. And it is much more applicable on direct solvent extraction as all the oil is already in miscella phase.
The refined oil from miscella refining is then bleached and deodorised easily.
Winterising can apply if necessary.

For fat uses, the oil is hydrogenated.

The cottonseeds may contain from 1 to 3% of gossypol, which is distributed in microscopic glands that one can observe by cutting the seed with a razor blade.
Ruminants do not have any problem with the free gossypol but the other animals feel toxic effects (like growing shortage) when they do eat those meals which contain a free gossypol level above 0.0.18%

In cooking, the free gossypol bounds with lysine (protein) and it diminishes the toxic effects on non-ruminants, but unfortunately detrimentally to the nutritional value of the meal.


End uses

Linters: Carpets - Low quality Textile – Cellulose – Collodion - Cellulose acetate
Hulls: Fertiliser – Used as Fuel
Meal: The protein content is 18-30% on undecorticated meal while it is of 35-45% on decorticated.
Oil: Salad oil – Cooking Oils – Ghee – Margarine - Shortening