The oil and fat products used for edible purposes can be divided into two distinct classes:

-liquid oils, such as olive oil, peanut oil, soybean oil, or sunflower oil; and -plastic fats, such as lard, shortening, butter, and margarine.

Fat and Oil Processing

Crude fat and oil derived from plant and animal sources are subjected to several commercial refining processes before the final products reach the consumer market.

During these processes, water, carbohydrates, proteins, pigments, as well as phospholipids, free fatty acids, sterols, waxes and tocopherols are removed.

In general, fat and oil undergo four processing steps:     1.    Extraction     2.    Refining (Neutralization or Degumming)    3.    Bleaching     4.    Deodorization

Fat and Oil Extraction

RenderingMechanical pressingSolvent extraction

Rendering

more often employed for the extraction of fats from animal tissues. 

oil-bearing tissues are chopped into small pieces and boiled in water  the oil floats to the surface of the water and skimmed 

water, carbohydrates, proteins, and phospholipids remain in the aqueous phase and are removed from the oil 

degumming is also performed during this step to remove excess phospholipids

the separated proteins are often used as animal feeds or fertilizers.

Mechanical Pressing

often used to extract oil from seeds and nuts 

shells or hulls of the plant materials are removed and the kernels or meats are grinded to rupture the cellular structures 

the coarse meal is then heated and pressed in hydraulic or screw presses to extract the oil

In some cases, oil is pressed without heating.  Such oil is known as cold-pressed or virgin oil.  It contains the least amount of impurities and is often of edible quality without further refining.

For seeds or nuts containing a higher oil content than soybeans it became customary to press the material in screw presses to remove a large proportion of the oil before extraction. Since this prepressing also ruptures the cellular structures of oil-bearing materials, most of the residual oil is easily removed with solvents

Solvent Extraction

For seeds or nuts containing a higher oil content, not all of the oil is removed during pressing. 

Organic solvents such as petroleum ether and hexane can be added to the pressed cake to recover the residual oil.  The oil-sovent solution will then be separated from the meal. 

Finally, the solvent is evaporated from the oil.

In general, fat and oil undergo four processing steps:     1.    Extraction     2.    Refining (Neutralization or Degumming)    3.    Bleaching     4.    Deodorization

Refining (Neutralization or Degumming)

Free fatty acids, phospholipids, pigments, and waxes in the extracted oil lead to undesirable properties of the final products.  Many of these impurities can be removed by treating fats at 40º to 85º C with caustic soda (sodium hydroxide) or soda ash (sodium carbonate).   

In general, fat and oil undergo four processing steps:     1.    Extraction     2.    Refining (Neutralization or Degumming)    3.    Bleaching     4.    Deodorization

Bleaching

Bleaching The major purpose of bleaching is the removal or undesire color materials in the oil. 

Heated oil (~85 oC) may be treated with various bleaching agents such as fuller's earth, activated carbon, or activated clays.

Many impurities, including chlorophyll and carotenoid pigments, are adsorbed onto such agents and removed by filtration.

However, bleaching also promotes lipid oxidation since some

natural antioxidants are removed together with the impurities.

In general, fat and oil undergo four processing steps:     1.    Extraction     2.    Refining (Neutralization or Degumming)    3.    Bleaching     4.    Deodorization

Deodorization Deodorization is the final step in the refining of oils.

Deodorization involves the use of steam distillation under reduced pressure. 

In Europe, a deodorization temperature of 175 - 205º C is common, but in the United States, higher temperatures of 235 - 250º C are usually employed.

Volatile compounds with undesirable odors and tastes can be driven off, resulting a odorless product.  The oil produced is referred to as "refined oil" and is ready to be consumed or for the manufacture of other products.  About 0.01 percent of citric acid is often added during this step to

inactivate pro-oxidant metals such as iron or copper.

FoodPercentages of Trans-Fatty Acids

Butter 3.6

Soft Margarine, High in PUFA 5.2

Soft Margarine, Low in PUFA 9.1

Hard Margarine 12.4

Vegetable Oils, Including Safflower, Sunflower, and Soy 0.0

Beefburger, Fried or Grilled 0.8

Chocolate Cake with Icing 7.1

Trans fat has both the benefits and drawbacks of a saturated fat.

- It has a longer shelf life than regular vegetable fat and is solid at room temperature.

-Trans fat tends to raise "bad" LDL- cholesterol and lower "good" HDL-cholesterol, although not as much as saturated fat.

-Trans fat is found in margarine, baked goods such as doughnuts and Danish pastry, deep-fried foods like fried chicken and French-fried potatoes, snack chips, imitation cheese, and confectionary fats.

These processes are used to modify physical properties of an oil or fat such as melting point and consistency.

Polymerization of oils

Polymerization of oils

Peroxide valueAnisidine valueThiobarbituric value

High saponification value means….

Iodine Value

High iodine value means…..

High AV means…….

Free fatty acid value

Example: Tripalmitin sample has an AV of 0.025. What is the free fatty acid value?

Peroxide value (PV)

Anisidine value

Measure……