Oil Extraction and Processing Questions and Answers

Answer: C

Correct answer: Phospholipids

Degumming removes phospholipids, also called phosphatides or gums. Water is mixed into the warm crude oil so that the hydratable phosphatides swell, become insoluble in oil, and can be separated by centrifuge.

Removing them matters because they would otherwise settle in storage, foul heat-exchange surfaces and darken the oil during deodorisation. The recovered gums are a saleable product - soya lecithin comes from exactly this stream. Colour is removed by bleaching, odour by deodorisation and free fatty acids by neutralisation, each in its own step.

Answer: D

Caustic soda converts the free acids to soaps that are separated by centrifuge, and the loss includes some neutral oil carried with them. Physical refining strips the acids by steam distillation instead and avoids the soapstock altogether.

Answer: A

Bleaching earth or activated carbon is mixed with the oil under vacuum and then filtered out, carrying the impurities with it. It also removes peroxides and traces of metals that would otherwise catalyse oxidation later.

Answer: B

Volatile aldehydes, ketones and remaining free fatty acids are stripped off by steam at low absolute pressure, which keeps the required temperature down. It is the last major step and largely determines the oil's flavour and shelf life.

Answer: C

The oil is chilled slowly so the high-melting fractions crystallise and can be filtered off, leaving a product that stays clear in a refrigerator. Sunflower and rice bran oils need it particularly because of their wax content.

Answer: D

Correct answer: Hydrolytic deterioration

Free fatty acids arise when triglycerides are split by water, usually with lipase as the catalyst, so their level records how much hydrolysis the oil has undergone. It is a history of storage conditions: damp seed, delayed processing and warm storage all raise it.

Oxidative deterioration is a separate pathway measured by peroxide value for the primary stage and anisidine value for the secondary. Free fatty acids matter commercially as well as technically, since every point of acidity must be neutralised, and neutralisation removes some neutral oil along with it.

Answer: A

Correct answer: The extent of primary oxidation

Peroxide value measures hydroperoxides, the first products formed when oxygen attacks the unsaturated fatty acid chains. It is therefore an index of primary oxidation and an early warning of rancidity to come.

It has a limitation worth knowing: hydroperoxides are unstable and decompose into aldehydes and ketones, so a badly deteriorated oil can show a falling peroxide value as oxidation proceeds. That is why it is read alongside anisidine value, which measures those secondary products. Hydrolytic deterioration is measured by free fatty acid content instead.

Answer: B

Correct answer: The degree of unsaturation

Iodine value is the mass of iodine, in grams, that will add to 100 grams of oil. Halogen adds across carbon-carbon double bonds, so the number is a direct measure of unsaturation.

It sorts oils into families - coconut around 8, groundnut near 90, soybean around 130, linseed above 170 - and predicts their behaviour: high values mean liquid at room temperature and prone to oxidation, low values mean solid and stable. Saponification value measures average chain length instead, and oxidation is measured by peroxide value.

Answer: C

Correct answer: Lipase raises free fatty acids quickly

Milling breaks the bran cells and brings a very active lipase into contact with the oil. Hydrolysis begins at once, and free fatty acids can rise by several per cent a day - a rate no other common oilseed approaches.

The consequence is commercial. High acidity means heavy refining losses, since every point of acid must be neutralised and neutral oil is lost with it, so bran left standing may become fit only for industrial use. The remedy is either immediate extraction or stabilisation of the bran by heat to denature the enzyme.

Answer: D

A seed carrying forty per cent oil floods a solvent extractor and drains poorly, so most of the oil is pressed out first and only the remainder is extracted. Low-oil seeds such as soybean go straight to direct extraction.