Processing of edible Oil and Fat

REFINING• Refining produces an edible oil with characteristics that consumers desire

such as bland flavor and odor, clear appearance, light color, stability to oxidation and suitability for frying.• In a refining process comprising the following steps:

1. Lecithin removal2. Degumming3. Free fatty acid removal4. Bleaching5. Deodorization

• The following precautionary measures are taken during refining in order to avoid undesirable autoxidation and polymerization reactions:

1. Absence of oxygen2. Avoidance of heavy metal contaminations3. Maintaining the processing temperature as low and duration as

short as possible.

1.Removal of lecithin

• This processing step is special importance for soybean oils .

• Water (2-3%) is added to crude oil, thereby enriching the phospholipids in the oil/water interface.

• The emulsion thus formed is heated up to 80 nd then separated or clarified by centrifugation.

2.Degumming

• Finely dispersed protein and carbohydrate are coagulated in oil by addition of phosphoric acid ( 0.1 % of oil weight ).

• A filtering aid is then added and the oil is clarified by filteration.

3.Removal of Free Fatty Acids( deacidification ) • The removal of fatty acids with 15 % sodium hydroxide (alkali refining)

is most frequently used method.• Technically , this is not very simple since fat hydrolysis has to be

avoided and , moreover , the sodium soap which tends to forms\ stable emulsions , has to be washed out by hot water. • After vacuum drying , the fat or oil may contain only about 0.05 %

free fatty acids and 60 to 70 ppm of sodium soaps.• When fat or oil is treated with diluted phosphoric acid , the content of

sodium soaps decreases to 20 ppm and part of the trace heavy-metal ions is removed.

4.Bleaching

• In order to remove the plant pigment (chlorophyll , carotenoids ) and autoxidation products, the fat or oil is stirred for 30 min in the presence of Al-silicates ( bleaching or Fuller’s earth ) in a vacuum at 90.

• The bleached oil is removed from the adsorbent by filteration .

• The retained by the absorbent can be recovered by hexane extraction and recycled into refining process.

5.Deodorization

• Deodorization is esentially vacuum steam distillation ( 190-230 0.5-10 mbar ) .

• The volatile compounds , together with undesirable odorants present in the fat or oil , are separated in refining steps

• Deodorization takes place min 20 in to 6 h depending on the type of fat or oil and the content of volatile compounds.

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