How to preserve nutrients while preparing food?

1. When peeling skin of vegetables do peel as thinly as possible. The nutrients in fruits and vegetables are concentrated just below the skin.

2. Do not cut vegetables into very small cubes as the surface area f vegetables interact with oxygen and destroy vitamins

3. Do not soak vegetables in water to prevent discoloration (browning). 40% of water soluble vitamins are lost during soaking. If you must soak, use the soaked water t knead dough and prepare soup and gravies.

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Traditional Ghani Technology

Ghani technology is the traditional method of extraction of oil from oil seeds like sesame, mustard, rapeseed etc. by use of simple technology. In this technology, oilseeds are held in scoped circular pit in the center of mortar made of stone or wood. In it works a stout upright pestle which descends from tip curved or angled piece. The pestle rests in a scooped out hollow that also permits pestle to rotate. Today the single angled piece takes the form of two shorter pieces chained together. The bottom of lower angled piece is attached to a load beam. One end of load beam rides around the outside of barrel while other is yoked to animal. The load beam is weighted down either with heavy stones or even seated operator. As the animal moves in circular ambit, the pestle rotates exerting lateral pressure on the upper chest of the pit, first pulverizing the oilseed and then crushing out its oil. Read more

Rendering and Hot Water Extraction

Rendering is the process of extraction of fat from animal tissue by application of heat. Rendering is also called trying. During rendering fat cells are ruptured, expelled and water evaporated. The accompanying connective tissues are separated as solid residue called cracklings. Rendering can be done by following two methods;

  1. Wet rendering
  2. Dry rendering

Wet rendering:

Fig: Autoclave for wet rendering

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Manufacture of edible oil: Solvent extraction

Material containing low amount of oil such as oilseed cake (meal) and rice bran are suitable for solvent extraction. Hexane is most widely used solvent and this process can extract oil form feed until oil present in feed is reduced to 0.5 % or less.


Perforated basket attached in conveyor belts holds the feed. Fresh warm solvent is sprayed from the top. Hexane is used as solvent whose boiling point is nearly 60°C. The basket moves up carrying the feed which is extracted through screen at the bottom of basket. The residue is treated with fresh solvent and finally defatted cake is obtained. The half miscella is recirculated through pump and again comes in contact with solvent. The full miscella is evaporated, refined, bleached and deodorized to obtain refined bleached and deodorized (RBD) oil.


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Manufacture of edible oil: Screw press method

Extraction of fat from different sources like oilseeds, nuts, oil containing fruits, animal fat are different and use different techniques.

  1. Animal fat is extracted by rendering technique that uses heating (moist/dry) fatty tissue.
  2. Oil from oilseeds and nuts is extracted by using mechanical expellers (screw press) that can extract 90 – 95 % oil in seed.
  3. Oil from oil cakes and bran is extracted by solvent extraction using hexane as solvent.
  4. Oil from flesh of fruits is extracted by using hot water extraction technique where flesh of fruit is macerated in hot water and extracted oil can be recovered by settling or centrifugation method.

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