A vegetable oil is a
triglyceride extracted from a plant. Such oils have been part of human culture
for millennia.The term "vegetable oil" can be narrowly defined as referring
only to plant oils that are liquid at room temperature, or broadly defined
without regard to a substance's state of matter at a given temperature. For
this reason, vegetable oils that are solid at room temperature are sometimes
called vegetable fats. Vegetable oils are composed of triglycerides, as
contrasted with waxes which lack glycerin in their structure. Although many
plant parts may yield oil, in commercial practice, oil is extracted primarily
from seeds.
On food packaging,
the term "vegetable oil" is often used in ingredients lists instead
of specifying the exact plant being used.
Uses of triglyceride
vegetable oil
Oils extracted from
plants have been used since ancient times and in many cultures. As an example,
in a 4,000-year-old kitchen unearthed in Indiana's Charlestown State Park,
archaeologist Bob McCullough of Indiana University-Purdue University Fort Wayne
found evidence that natives used large slabs of rock to crush hickory nuts,
then boiled them in water to extract the oil.
Culinary uses
Many vegetable oils
are consumed directly, or indirectly as ingredients in food – a role that they
share with some animal fats, including butter and ghee. The oils serve a number
of purposes in this role:
Shortening – to give pastry a crumbly
texture.
Texture – oils can serve to make other
ingredients stick together less.
Flavor – while less-flavorful oils command
premium prices[citation needed], some oils, such as olive, sesame, or almond
oil, may be chosen specifically for the flavor they impart.
Flavor base – oils can also
"carry" flavors of other ingredients, since many flavors are present
in chemicals that are soluble in oil.
Secondly, oils can be
heated and used to cook other foods. Oils suitable for this objective must have
a high flash point. Such oils include the major cooking oils – soybean, canola,
sunflower, safflower, peanut, cottonseed, etc. Tropical oils, such as coconut,
palm, and rice bran oils, are particularly valued in Asian cultures for high
temperature cooking, because of their unusually high flash point.
Hydrogenated oils
Unsaturated vegetable
oils can be transformed through partial or complete "hydrogenation"
into oils of higher melting point. The hydrogenation process involves
"sparging" the oil at high temperature and pressure with hydrogen in
the presence of a catalyst, typically a powdered nickel compound. As each
carbon–carbon double-bond is chemically reduced to a single bond, two hydrogen
atoms each form single bonds with the two carbon atoms. The elimination of
double bonds by adding hydrogen atoms is called saturation; as the degree of
saturation increases, the oil progresses toward being fully hydrogenated. An
oil may be hydrogenated to increase resistance to rancidity (oxidation) or to
change its physical characteristics. As the degree of saturation increases, the
oil's viscosity and melting point increase.
The use of
hydrogenated oils in foods has never been completely satisfactory. Because the
center arm of the triglyceride is shielded somewhat by the end fatty acids,
most of the hydrogenation occurs on the end fatty acids, thus making the
resulting fat more brittle[citation needed]. A margarine made from naturally
more saturated oils will be more plastic (more "spreadable") than a
margarine made from hydrogenated soy oil[citation needed]. While full
hydrogenation produces largely saturated fatty acids, partial hydrogenation
results in the transformation of unsaturated cis fatty acids to trans fatty
acids in the oil mixture due to the heat used in hydrogenation. Partially
hydrogenated oils and their trans fats have been linked to an increased risk of
mortality from coronary heart disease (CHD)., among other increased health
risks.
In the US, the
Standard of Identity for a product labeled as "vegetable oil margarine"
specifies only canola, safflower, sunflower, corn, soybean, or peanut oil may be
used. Products not labeled "vegetable oil margarine" do not have that
restriction.
Industrial uses
Vegetable oils are
used as an ingredient or component in many manufactured products.
Many vegetable oils
are used to make soaps, skin products, candles, perfumes and other personal
care and cosmetic products. Some oils are particularly suitable as drying oils,
and are used in making paints and other wood treatment products. Dammar oil (a
mixture of linseed oil and dammar resin), for example, is used almost
exclusively in treating the hulls of wooden boats. Vegetable oils are
increasingly being used in the electrical industry as insulators as vegetable
oils are not toxic to the environment, biodegradable if spilled and have high
flash and fire points. However, vegetable oils are less stable chemically, so
they are generally used in systems where they are not exposed to oxygen, and
they are more expensive than crude oil distillate. Synthetic tetraesters, which
are similar to vegetable oils but with four fatty acid chains compared to the
normal three found in a natural ester, are manufactured by Fischer
esterification. Tetraesters generally have high stability to oxidation and have
found use as engine lubricants. Vegetable oil is being used to produce
biodegradable hydraulic fluid and
lubricant.
One limiting factor
in industrial uses of vegetable oils is that all such oils eventually
chemically decompose, turning rancid. Oils that are more stable, such as ben
oil or mineral oil, are preferred for some industrial uses.
Vegetable-based oils,
like castor oil, have been used as medicine and as lubricants for a long time.
Castor oil has numerous industrial uses, primarily due to the presence of
hydroxyl groups on the fatty acid chains. Castor oil, and other vegetable oils
which have been chemically modified to contain hydroxyl groups, are becoming
increasingly important in the production of polyurethane plastic for many applications.
These modified vegetable oils are known as natural oil polyols.
Pet food additive
Vegetable oil is used
in production of some pet foods. AAFCO defines vegetable oil, in this context,
as the product of vegetable origin obtained by extracting the oil from seeds or
fruits which are processed for edible purposes. In some poorer grade pet foods,
the oil is listed only as "vegetable oil", without specifying the
particular oil.
Fuel
Vegetable oils are
also used to make biodiesel, which can be used like conventional diesel. Some
vegetable oil blends are used in unmodified vehicles but straight vegetable
oil, also known as pure plant oil, needs specially prepared vehicles which have
a method of heating the oil to reduce its viscosity. The vegetable oil economy
is growing and the availability of biodiesel around the world is increasing.
The NNFCC estimate
that the total net greenhouse gas savings when using vegetable oils in place of
fossil fuel-based alternatives for fuel production, range from 18 to 100%.
Production
The production
process of vegetable oil involves the removal of oil from plant components,
typically seeds. This can be done via mechanical extraction using an oil mill
or chemical extraction using a solvent. The extracted oil can then be purified
and, if required, refined or chemically altered.
Mechanical extraction
Oils can also be
removed via mechanical extraction, termed "crushing" or
"pressing." This method is typically used to produce the more
traditional oils (e.g., olive, coconut etc.), and it is preferred by most
"health-food" customers in the United States and in Europe.[citation
needed] There are several different types of mechanical extraction.
Expeller-pressing extraction is common, though the screw press, ram press, and
Ghani (powered mortar and pestle) are also used. Oilseed presses are commonly
used in developing countries, among people for whom other extraction methods
would be prohibitively expensive; the Ghani is primarily used in India. The
amount of oil extracted using these methods varies widely, as shown in the following
table for extracting mowrah butter in India:
Method Percentage extracted
Ghani[15] 20–30%
Expellers 34–37%
Solvent 40–43%
Solvent extraction
The processing
vegetable oil in commercial applications is commonly done by chemical
extraction, using solvent extracts, which produces higher yields and is quicker
and less expensive. The most common solvent is petroleum-derived hexane. This
technique is used for most of the "newer" industrial oils such as
soybean and corn oils.
Supercritical carbon
dioxide can be used as a non-toxic alternative to other solvents.
Hydrogenation
Oils may be partially
hydrogenated to produce various ingredient oils. Lightly hydrogenated oils have
very similar physical characteristics to regular soy oil, but are more
resistant to becoming rancid. Margarine oils need to be mostly solid at 32 °C
(90 °F) so that the margarine does not melt in warm rooms, yet it needs to be
completely liquid at 37 °C (98 °F), so that it doesn't leave a
"lardy" taste in the mouth.
Hardening vegetable
oil is done by raising a blend of vegetable oil and a catalyst in near-vacuum
to very high temperatures, and introducing hydrogen. This causes the carbon
atoms of the oil to break double-bonds with other carbons, each carbon forming
a new single-bond with a hydrogen atom. Adding these hydrogen atoms to the oil
makes it more solid, raises the smoke point, and makes the oil more stable.
Hydrogenated
vegetable oils differ in two major ways from other oils which are equally
saturated. During hydrogenation, it is easier for hydrogen to come into contact
with the fatty acids on the end of the triglyceride, and less easy for them to
come into contact with the center fatty acid. This makes the resulting fat more
brittle than a tropical oil; soy margarines are less
"spreadable"[compared to?]. The other difference is that trans fatty
acids (often called trans fat) are formed in the hydrogenation reactor, and may
amount to as much as 40 percent by weight of a partially hydrogenated oil.
Hydrogenated oils, especially partially hydrogenated oils with their higher
amounts of trans fatty acids are increasingly thought to be unhealthy.
Sparging
In the processing of
edible oils, the oil is heated under vacuum to near the smoke point, and water
is introduced at the bottom of the oil. The water immediately is converted to
steam, which bubbles through the oil, carrying with it any chemicals which are
water-soluble. The steam sparging removes impurities that can impart unwanted
flavors and odors to the oil.
Particular oils
For a more
comprehensive list, see List of vegetable oils.
The following
triglyceride vegetable oils account for almost all worldwide production, by
volume. All are used as both cooking oils and as SVO or to make biodiesel.
According to the USDA, the total world consumption of major vegetable oils in
2007/08 was:[17]
Oil source World consumption
(million metric tons)
Notes
Palm 41.31 The
most widely produced tropical oil, also used to make biofuel
Soybean 41.28 Accounts for about half of worldwide edible oil production
Rapeseed 18.24 One of the most widely used cooking oils, canola is a variety
(cultivar) of rapeseed
Sunflower seed 9.91 A common cooking oil, also used to make biodiesel
Peanut 4.82 Mild-flavored cooking oil
Cottonseed 4.99 A
major food oil, often used in industrial food processing
Palm kernel 4.85 From
the seed of the African palm tree
Coconut 3.48 Used in soaps and cooking
Olive 2.84 Used
in cooking, cosmetics, soaps and as a fuel for traditional oil lamps
Note that these
figures include industrial and animal feed use. The majority of European
rapeseed oil production is used to produce biodiesel, or used directly as fuel
in diesel cars which may require modification to heat the oil to reduce its
higher viscosity. The suitability of the fuel should come as little surprise,
as Rudolf Diesel originally designed his engine to run on peanut oil.
Other significant
triglyceride oils include:
Corn oil, one of the most common cooking
oils. As of 2006 the US produced about 1.09 million metric tons of corn oil, which is used for cooking oil,
salad dressing, margarine, mayonnaise, prepared goods like spaghetti sauce and
baking mixes, and to fry prepared foods like potato chips and French fries.
Grape seed oil, used in cooking and
cosmetics
Hazelnut and other nut oils
Linseed oil, from flax seeds
Rice bran oil, from rice grains
Safflower oil, a flavorless and colorless
cooking oil
Sesame oil, used as a cooking oil, and as a
massage oil, particularly in India
Composition of fats
Vegetable oils
Type Processing
Treatment Saturated
fatty acids[19] Mono-
unsaturated
fatty acids[19] Polyunsaturated fatty acids Oleic acid
(ω-9) Smoke point
Total poly[19] linolenic acid
(ω-3) Linoleic acid
(ω-6)
Canola (rapeseed) - 7.365
63.276 28.142 9-11 19-21 -
400 °F (204 °C)[20]
Coconut - 91.00
6.000 3.000
- 2
6 350 °F (177 °C)[20]
Corn - 12.948
27.576 54.677
1 58
28 450 °F (232 °C)[21]
Cottonseed - 25.900
17.800 51.900
1 54
19 420 °F (216 °C)[21]
Flaxseed/Linseed
(European) - 6 - 9 10 -
22 68 - 89 56 - 71 12 - 18 10 - 22 225
°F (107 °C)
Olive - 14.00
72.00 14.00
<1.5 9–20 - 380 °F (193 °C)[20]
Palm - 49.300
37.000 9.300
- 10
40 455 °F (235 °C)[23]
Peanut - 16.900 46.200 32.000 -
32 48 437 °F
(225 °C)[21]
Safflower (>70%
linoleic) - 8.00 15.00 75.00 - -
- 410 °F (210 °C)[20]
Safflower (high
oleic) - 7.541 75.221 12.820 -
- - 410
°F (210 °C)[20]
Soybean - 15.650
22.783 57.740
7 50
24 460 °F (238 °C)
Sunflower (<60%
linoleic) - 10.100 45.400 40.100 0.200 39.800
45.300 440
°F (227 °C)
Sunflower (>70%
oleic) - 9.859 83.689 3.798 - -
- 440 °F (227 °C)
Cottonseed
(hydrogenated) Hydrogenated 93.600 1.529
.587 .287
Palm (hydrogenated) Hydrogenated 47.500
40.600 7.500
Soybean
(hydrogenated) Hydrogenated 21.100 73.700
.400 .096
Values as percent (%)
by weight of total fat.
History in North
America
While olive oil and
other pressed oils have been around for millennia, Procter & Gamble
researchers were innovators when they started selling cottonseed oil as a
creamed shortening, in 1911. Ginning mills were happy to have someone haul away
the cotton seeds. Procter & Gamble researchers learned how to extract the
oil, refine it, partially hydrogenate it (causing it to be solid at room
temperature and thus mimic natural lard), and can it under nitrogen gas.
Compared to the rendered lard Procter & Gamble was already selling to
consumers, Crisco was cheaper, easier to stir into a recipe, and could be
stored at room temperature for two years without turning rancid. (Procter &
Gamble sold their fats and oils brands – Jif and Crisco – to The J.M. Smucker
Co. in 2002.)
Soybeans were an
exciting new crop from China in the 1930s. Soy was protein-rich, and the medium
viscosity oil was high in polyunsaturates. Henry Ford established a soybean
research laboratory, developed soybean plastics and a soy-based synthetic wool,
and built a car "almost entirely" out of soybeans.[24] Roger Drackett
had a successful new product with Windex, but he invested heavily in soybean
research, seeing it as a smart investment. By the 1950s and 1960s, soybean oil
had become the most popular vegetable oil in the US.
In the mid-1970s,
Canadian researchers developed a low-erucic-acid rapeseed cultivar. Because the
word "rape" was not considered optimal for marketing, they coined the
name "canola" (from "Canada Oil low acid"). The U.S. Food
and Drug Administration approved use of the canola name in January 1985, and
U.S. farmers started planting large areas that spring. Canola oil is lower in
saturated fats, and higher in monounsaturates and is a better source of omega-3
fats than other popular oils. Canola is very thin (unlike corn oil) and
flavorless (unlike olive oil), so it largely succeeds by displacing soy oil,
just as soy oil largely succeeded by displacing cottonseed oil.
Used oil
A large quantity of
used vegetable oil is produced and recycled, mainly from industrial deep fryers
in potato processing plants, snack food factories and fast food restaurants.
Recycled oil has
numerous uses, including use as a direct fuel, as well as in the production of
biodiesel, soap, animal feed, pet food, detergent, and cosmetics. It's traded
as the commodity, yellow grease.
Since 2002, an
increasing number of European Union countries have prohibited the inclusion of
recycled vegetable oil from catering in animal feed. Used cooking oils from
food manufacturing, however, as well as fresh or unused cooking oil, continue
to be used in animal feed.
Negative health
effects
Hydrogenated oils
have been shown to cause what is commonly termed the "double deadly
effect", raising the level of LDLs and decreasing the level of HDLs in the
blood, increasing the risk of blood clotting inside blood vessels.
A high consumption of
oxidized polyunsaturated fatty acids (PUFAs), which are found in most types of
vegetable oil (e.g. soybean oil, corn oil – the most consumed in USA, sunflower
oil, etc.) may increase the likelihood that postmenopausal women will develop breast
cancer. A similar effect was observed on prostate cancer and skin cancer in
mice.
Vegetables oils high
in polyunsaturated fatty acids cause inflammation of the cells and may lead to
a digestive disease and eventually cancer. The main reason is that the
polyunsaturated fatty acids in vegetable oils autooxidize during food
processing when exposed to oxygen and/or UV radiation; resulting in the
autoproduction of inflammatory peroxides and hydroperoxides from polyunsaturated
fatty acids.
Product labeling
There is increasing
concern[by whom?] that the product labeling that includes "vegetable
fat" or "vegetable oil" in its list of ingredients masks the
identity of the fats or oils present. This has been made more pressing as
concerns have been raised over the social and environmental impact of palm oil
in particular, especially given the predominance of palm oil.
From 13 December 2014
all food products produced in the European Union will be legally required to
indicate the specific vegetable oil used in their manufacture, following the
introduction of the Food Information to Consumers Regulation
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