PLANTS AND PEOPLE
Hugh D. Wilson 

Oils and Waxes

Base structure:
 
 

GLYCEROL        FATTY ACID
 
 

      O H H H H H H H H H H H H H H H H H H
  |    || | | | | | | | | | | | | | | | | | |
H-C-OH HO-C-C-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-H
  | ----  | | | | | | | |     | | | | | | | |
  |       H H H H H H H H     H H H H H H H H
H-C-OH 
  |
  | 
H-C-OH
  |
 
H
 
 
 
Fatty Acids - Levels of Saturation:
 
[Stearic - saturated]
 
 O H H H H H H H H H H H H H H H H H H
|| | | | | | | | | | | | | | | | | | |
HO-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H 
   | | | | | | | | | | | | | | | | | |
   H H H H H H H H H H H H H H H H H H
 
[Oleic - unsaturated]:
 
 O H H H H H H H H H H H H H H H H H H
|| | | | | | | | | | | | | | | | | | |
HO-C-C-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-C-H
   | | | | | | | |     | | | | | | | |
   H H H H H H H H     H H H H H H H H

 
[Linoleic - more unsaturated]:
 
 O H H H H H H H H H H H H H H H H H H
|| | | | | | | | | | | | | | | | | | |
HO-C-C-C-C-C-C=C-C-C=C-C-C-C-C-C-C-C-C-H 
   | | | | |     |     | | | | | | | |
   H H H H H     H     H H H H H H H H

"Oil" - insoluble in water - type expressed from plants known as GLYCERIDES - do not diffuse in air [VOLATILE OILS], thus called FIXED, NEUTRAL, FATTY or NONVOLATILE. Composed of two kinds of compounds:

GLYCEROL - a three carbon alcohol that forms the BACKBONE - is the same for all oils:

FATTY ACIDS - hydrocarbon chain with a CARBOXYL GROUP [COOH] at one end that causes it to interact chemically as an acid. They attach to the glycerol with the release of a water molecule. Different properties of oils relate to number and chemical structure of fatty acids attached to the glycerol, i.e., TRIGLYCERIDE, DI-, MONO-, also:

UNSATURATED: [MONO, DI, POLYUNSATURATED]

Double bonds can be broken by addition of reactive compounds - iodine is added to assess amount of saturation - often in mixed oils - higher the number, higher the unsaturation. - range in edible oils goes from 7 to over 200.  See info on trans fatty acids.

Those ranging above 150 are 'drying' oils [many double bonds, link together in polymerization to form films]

150-100 = 'semi-drying',
100-70 = 'nondrying'
below 70 = fats because they are solid at room temp = highly saturated.

Processing:

1. Extraction (pressing/solvents)

2. degumming (mix with water at high temp (90-120F), centrifuge - removes mucilaginous material that might have been extracted with the oil - LECITHIN [A PHOSPHOGYLCERIDE] is recovered from the water fraction - mostly from soybean and other seed oils (compare to CAFFINE as an important BY-PRODUCT)

3. bleaching - mix with FULLER'S EARTH [DIATOMACEOUS EARTH] or charcoal and filtering - removes volatile oils and pigments [gossypol]

4. deodorizing - heat with steam under a vacuum

5. winterizing - chill and filter to remove 'clouding' stuff

HYDROGENATION - bubbling hydrogen gas through unsaturated oil to increase saturation [lower the iodine value] to produce a VEGETABLE FAT [solid at rm. temp] - discovered in early 1900s and generated a new industry - margarines and 'cheese foods'.

OXIDATION - iodine value is lowered by oxygen - causes problem with taste [='rancid']. Thus, synthetic ANTIOXIDANTS [BHT, BHA, polysorbate 80] often added as 'preservatives'.

Also chain length [number of carbon atoms] and chain structure [straight or branched] determine the characteristics of vegetable oils/fats..

USES: most vegetable oils used for food, but SOAPS:

'Soap' = metal salt of fatty acid, cleaved from the glycerol molecule by a strong base - usually sodium or potassium hydroxide - produces pure glycerol and sodium or potassium salt of the fatty acids that were previously attached in the oil. These salts are strongly bipolar with reagard to charge - HYDROPHOBIC [-] vs. HYDROPHILIC [+]. This creates a film on water - one end in the water, the other [hydrophobic] sticking out - and allows particles to be attracted and removed.

Why oils in plants? - Vegetable oils come almost exclusively from SEEDS. Stored in the ENDOSPERM (Caster Oil, Coconut), the sporophytic COTYLEDONS (Peanut, Soybean, Cotton) or the SCUTELLUM ["specialized single cotyledon of a grass embryo, adapted for the adsorption of food from the endosperm"] (Corn). Often the primary food for the embryo.

We use them for food - high caloric content (over twice the calories of starch) - SO, used for food by plants BUT not mature plant [photosynthetic], but embryo - especially those that tend to have mature embryos in the seed [usually extracted from cotyledons [Helianthus, Glycine, Gossypium, etc.]. Also sometimes found in the fruit [Olive] - possibly there to attract dispersers - a food reward.

PLANTS (overview)

Drying

Linum usitatissimum - Linaceae - LINSEED OIL - ancient element of the near eastern complex - possibly the oldest domesticated oil plant- large genus - several native to the local flora - high iodine value [204] - used today in paints and as a protective film - initial use was as an edible oil - plant also provides stem fiber = FLAX. LINOLEUM - fully oxidized vegetable oil mixed with ground cork or wood and pressed onto a felt, burlap, or canvas backing [process has been displaced by plastic floor coverings in this country]

Aleurites fordii - Euphorbiaceae - Asian Tree - Tung Oil - from seeds - India Ink, Chinese calligraphy - protective wood covering

Semi-drying

Carthamus tinctorius - Asteraceae [thistle like herb] - Safflower - eastern mediterranean - most unsaturated of the commonly used vegetable oils - has lots of LINOLEIC acid, one of the few fatty acids than cannot be synthesized by humans - - originally grown for dye pigments extrated from flowers [tinctorius] - now often found in cooking oil.

Glycine max - Originally used as forage [U.S.] and food [Asia] - now most important oil crop - most of the crop is processed for oil and 60% of all edible oil produced in this country comes from the soybean plant - processing requires cleaning because of AFLATOXINS - [Aspergillus flavus (compare with Aspergillus oryzae)] - used both the oil and the by-product of oil extraction [cake] as animal food [high protein]. Contains natural antioxidants - stores well and does not need chemical additives to protect against oxidation

Helianthus annuus - like the soybean, oil production is relative recent - USSR developed high-oil cultivars that are dwarfed to allow machine harvesting

Zea mays - oil production a by-product of starch production - thus, high oil cultivars not developed - embryo is separated during the milling process [de-germing].

Sesamum indicum - Pedaliaceae [related to Solanaceae] - SESAME OIL - origin unknown, but very early in near east - possibly originated in Ethiopia - not known from the wild - major oil plant, but mostly in old world - we know it mostly from the top of burger buns

Gossypium hirsutum - Malvaceae - as with corn, oil would not be a major product if the cotton were not an important crop, in this case for fiber - young american chemists - DAVID WESSON - experimented with purifying cotton seed oil - developed system in 1900 and marketed Wesson Oil. - also CRISCO was the first major 'vegetable lard' produced by hydrogenation of cotton seed oil [Proctor and Gamble - 1911].

Brassica napus (rape) or campestris (turnip) - used historically as both food and lubricant - unusual fatty acid - ERUCIC ACID - causes problems for food use [bad taste, possibly toxic], BUT has unusual propertities as a lubricant in that it can withstand high temps - combustion engines of the future will require oils with this capability - THUS, Brassica species are now the focus of attempts to develop high temp lubricants and other industrial oils via molecular biology.

Non-Drying

Arachis hypogaea - oil use starting by the French ca. 125 years ago - now most of the crop goes for oil - 1/4 of US crop goes for oil - prime cooking oil - 2nd only to soybean as world oil crop (see biodiesal).

Olea europea - Oleaceae - (family includes Fraxinus, Ligustrum) - very old [Crete, ca. 6k BP - not a major oil today - gourmet cooking - only one discussed that is taken from the pericarp


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