UNIT 1
Oils and Fats
WHAT IS OILS AND FATS
Oils and fats are organic substances that are useful in human
nutrient.
Oils and fats are distinguished by their phase. Oils are usually
liquid, while fats are solid.
Edible oils and fats are mostly produced by plants and animals.
However, they can be synthesized by chemical processes.
Oils and fats are mixtures of glyceryl esters of carboxylic acids,
compounds consisting of an aliphatic chain and a –COOH end.
Edible oils, with naturally occurring compound based on long chain
fatty acids and esters (particularly glycerides esters) as well as
derivatives such as glycerine, long chain fatty alcohols, sulfates and
sulfonates.
SOURCES OF OILS AND FATS
Fats & oils share a common molecular structure, which is represented by
the formula below:
This structural formula shows that fats and oils contain three ester
functional groups.
Fats and oils are esters of the tri-alcohol, glycerol (or glycerine). Therefore,
fats and oils are commonly called triglycerides, although a more accurate
name is triacylglycerols.
In the fatty acids, Ra, Rb, and Rc, represent groups of carbon and hydrogen
atoms in which the carbon atoms are attached to each other in an
unbranched chain.
Chemically, fats and oils are called “triglycerides.” They
are esters of glycerol, with a varying blend of fatty acids.
Fig. Chemical structure of triglyceride, pointing out fatty
acid parts and glycerol part.
FATTY ACIDS
Essentially, fatty acids are long chain hydrocarbons with
a carboxylic acid.
Fatty acids can be saturated (with hydrogen bonds) or
unsaturated (with some double bonds between carbon
atoms).
INDUSTRIAL USES
GENERAL FLOW OF OILS AND FATS PROCESSING
FLAKING
After hulling, the seeds, are reduced in size or flaked to facilitate oil
removal.
This rolling process minimizes the distance through which the free oil
must pass, but it does not necessarily rupture the walls of the oil cells.
Proper moisture content of the seeds is essential for flaking, and if the
moisture level is too low, the seeds must be conditioned to raise the
moisture to about 11%.
Seeds may be flaked by passing between two rolls mounted side-by-
side; however, they are more often flaked in a series of five stacked-
crushing rolls because a thinner flake may be achieved with the
vertical rolls.
For mechanical pressing, a thickness of 0.127–0.254 mm is common,
and for solvent extraction, flakes of not less than 0.230–0.254 mm
REMOVAL OF OIL FROM SEEDS
Expression: More pressure and more heat generation resulting more
disintegration
For seeds having high oil content
Usually Mechanical pressing method provides yields of only 65-70% of the
oil and 80% is considered very good.
Solvent extraction is a continuous chemical process for processing oil
seeds such as ground-nut, soya bean and rapeseed as opposed
physical crushing for oil extraction.
For low oil content
Meal contains less than 1% oil
For high oil content seeds, such as cottonseeds and safflower seed, usually
both expression and extraction are utilized in the recovery systems for
higher yields.
1) Hydraulic pressing:
Batch pressing was the earliest commercial method of oil
extraction.
Hydraulic equipment replaced the mechanical operations and
the method became known as hydraulic pressing.
In open presses, oilseed meals were wrapped in cloths and
placed between plates, which were then gradually compressed
to squeeze the oil from the seeds.
Box-type presses were most often used for cottonseed, and this
method was fairly labor intensive.
2) Screw Pressing
With this system, pressure is gradually applied to the flakes as
a screw conveys them from the feed end to the discharge end of
the expeller barrel.
About 3–4% oil remains in the cake that results from screw
pressing.
this type of presses exert 680–1089 atm (5–8 tons per square
inch) pressure on the flakes.
3) Direct Solvent
This process is based on the use of a nonpolar solvent, specifically hexane,
to dissolve the oil without removing proteins and other compounds.
The flakes are mixed with hexane in a batch or continuous operation.
The resulting oil-solvent micelle and the residual meal are heated to
evaporate the solvent, which is collected and reused. Solvent extraction
yields about 11.5% more oil than does the screw-press method, and 1% or
less oil remains in the meal.
4) Prepress Solvent Extraction
With prepress solvent extraction, cottonseeds are pressed to remove most of
the oil and then the oil remaining in the press-cake is extracted with
solvent. This solvent extraction operates on a reduced volume of feed stock
(i.e., press-cake, as opposed to full-fat flakes) and, therefore, requires a
modest size extractor with modest amounts of desolventizer and solvent.
METHODS OF EXTRACTING VEGETABLE OILS
Fig. Vegetable oil extraction methods
PROCESS DESCRIPTION
ASSIGNMENT
Briefly explain the types of extractor used in
solvent extraction of oil.
Write advantages and disadvantages of
mechanical pressing method and solvent
extraction method.
