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Fatty acid

2007 Schools Wikipedia Selection. Related subjects: Food and agriculture;
Health and medicine

      Types of Fats in Food
     * Unsaturated fat
          + Monounsaturated fat
          + Polyunsaturated fat
          + Trans fat
          + Omega: 3, 6, 9
     * Saturated fat

            See Also
     * Fatty acid
     * Essential fatty acid

   In chemistry, especially biochemistry, a fatty acid is a carboxylic
   acid often with a long unbranched aliphatic tail ( chain), which is
   either saturated or unsaturated. Carboxylic acids as short as butyric
   acid (4 carbon atoms) are considered to be fatty acids, while fatty
   acids derived from natural fats and oils may be assumed to have at
   least 8 carbon atoms, e.g. caprylic acid (octanoic acid). Most of the
   natural fatty acids have an even number of carbon atoms, because their
   biosynthesis involves acetyl-CoA, a coenzyme carrying a two-carbon-atom
   group.

   Industrially, fatty acids are produced by the hydrolysis of the ester
   linkages in a fat or biological oil (both of which are triglycerides),
   with the removal of glycerol. See oleochemicals.

Types of fatty acids

   Several fatty acid molecules
   Several fatty acid molecules

Saturated fatty acids

   Saturated fatty acids do not contain any double bonds or other
   functional groups along the chain. The term "saturated" refers to
   hydrogen, in that all carbons (apart from the carboxylic acid [-COOH]
   group) contain as many hydrogens as possible. In other words, the omega
   (ω) end contains 3 hydrogens (CH[3]-) and each carbon within the chain
   contains 2 hydrogen

   Saturated fatty acids form straight chains and, as a result, can be
   packed together very tightly, allowing living organisms to store
   chemical energy very densely. The fatty tissues of animals contain
   large amounts of long-chain saturated fatty acids. In IUPAC
   nomenclature, fatty acids have an [-oic acid] suffix. In common
   nomenclature, the suffix is usually -ic.

   The shortest descriptions of fatty acids include only the number of
   carbon atoms and double bonds in them (e.g. C18:0 or 18:0). C18:0 means
   that the carbon chain of the fatty acid consists of 18 carbon atoms and
   there are no (zero) double bonds in it, whereas C18:1 describes an
   18-carbon chain with one double bond in it. Each double bond can be
   either in a cis- or trans- conformation and in a different position
   with respect to the ends of the fatty acid, therefore, not all C18:1s,
   for example, are identical. If there is one or more double bonds in the
   fatty acid, it is no longer considered saturated, rather it makes it
   mono- or polyunsaturated.

   Most commonly occurring saturated fatty acids are:
   This is a computer generated image of Dodecanoic Acid, a fatty acid.
   Enlarge
   This is a computer generated image of Dodecanoic Acid, a fatty acid.
     * Butyric (butanoic acid): CH[3](CH[2])[2]COOH or C4:0
     * Caproic (hexanoic acid): CH[3](CH[2])[4]COOH or C6:0
     * Caprylic (octanoic acid): CH[3](CH[2])[6]COOH or C8:0
     * Capric (decanoic acid): CH[3](CH[2])[8]COOH or C10:0
     * Lauric (dodecanoic acid): CH[3](CH[2])[10]COOH or C12:0
     * Myristic (tetradecanoic acid): CH[3](CH[2])[12]COOH or C14:0
     * Palmitic (hexadecanoic acid): CH[3](CH[2])[14]COOH or C16:0
     * Stearic (octadecanoic acid): CH[3](CH[2])[16]COOH or C18:0
     * Arachidic (eicosanoic acid): CH[3](CH[2])[18]COOH or C20:0
     * Behenic (docosanoic acid): CH[3](CH[2])[20]COOH or C22:0

Unsaturated fatty acids

   Unsaturated fatty acids are of similar form, except that one or more
   alkenyl functional groups exist along the chain, with each alkene
   substituting a singly- bonded " -CH[2]-CH[2]-" part of the chain with a
   doubly-bonded "-CH=CH-" portion (that is, a carbon double bonded to
   another carbon).

   The two next carbon atoms in the chain that are bound to either side of
   the double bond can occur in a cis or trans configuration.

   cis
          A cis configuration means that the two carbons are on the same
          side of the double bond. The rigidity of the double bond freezes
          its conformation and, in the case of the cis isomer, causes the
          chain to bend and restricts the conformational freedom of the
          fatty acid. The more double bonds the chain has in the cis
          configuration, the less flexibility it has. When a chain has
          many cis bonds, it becomes quite curved in its most accessible
          conformations. For example, oleic acid, with one double bond,
          has a "kink" in it, while linoleic acid, with two double bonds,
          has a more pronounced bend. Alpha-linolenic acid, with three
          double bonds, favors a hooked shape. The effect of this is that
          in restricted environments, such as when fatty acids are part of
          a phospholipid in a lipid bilayer, or triglycerides in lipid
          droplets, cis bonds limit the ability of fatty acids to be
          closely packed and therefore could affect the melting
          temperature of the membrane or of the fat.

   trans
          A trans configuration, by contrast, means that the next two
          carbon atoms are bound to opposite sides of the double bond. As
          a result, they don't cause the chain to bend much, and their
          shape is similar to straight saturated fatty acids.

   In most naturally occurring unsaturated fatty acids, each double bond
   has 3n carbon atoms after it, for some n, and all are cis bonds. Most
   fatty acids in the trans configuration (trans fats) are not found in
   nature and are the result of human processing (eg, hydrogenation).

   The differences in geometry between the various types of unsaturated
   fatty acids, as well as between saturated and unsaturated fatty acids,
   play an important role is biological processes, and in the construction
   of biological structures (such as cell membranes).

Nomenclature

   There are two different ways to make clear where the double bonds are
   located in molecules. For example:
     * cis/trans-Delta-x or cis/trans-Δ^x: The double bond is located on
       the xth carbon-carbon bond, counting from the carboxyl terminus.
       The cis or trans notation indicates whether the molecule is
       arranged in a cis or trans conformation. In the case of a molecule
       having more than one double bond, the notation is, for example,
       cis,cis-Δ^9,Δ^12.
     * Omega-x or ω-x : A double bond is located on the xth carbon-carbon
       bond, counting from the ω, (methyl carbon) end of the chain.
       Sometimes, the symbol ω is substituted with a lowercase letter n,
       making it n-6 or n-3.

   Examples of unsaturated fatty acids:
     * Oleic acid: CH[3](CH[2])[7]CH=CH(CH[2])[7]COOH or cis-Δ^9 C18:1
     * Linoleic acid: CH[3](CH[2])[4]CH=CHCH[2]CH=CH(CH[2])[7]COOH or
       C18:2
     * Alpha-linolenic acid:
       CH[3]CH[2]CH=CHCH[2]CH=CHCH[2]CH=CH(CH[2])[7]COOH or C18:3
     * Arachidonic acid
       CH[3](CH[2])[4]CH=CHCH[2]CH=CHCH[2]CH=CHCH[2]CH=CH(CH[2])[3]COOH^
       NIST or C20:4
     * Eicosapentaenoic acid or C20:5
     * Docosahexaenoic acid or C22:6
     * Erucic acid: CH[3](CH[2])[7]CH=CH(CH[2])[11]COOH or C22:1

   Alpha-linolenic, docosahexaenoic, and eicosapentaenoic acids are
   examples of omega-3 fatty acids. Linoleic acid and arachidonic acid are
   omega-6 fatty acids. Oleic and erucic acid are omega-9 fatty acids.
   Stearic and oleic acid are both 18 C fatty acids. They differ only in
   that stearic acid is saturated with hydrogen, while oleic acid is an
   unsaturated fatty acid with two fewer hydrogens.

Essential fatty acids

   The human body can produce all but two of the fatty acids it needs.
   These two, linoleic acid and alpha-linolenic acid, are widely
   distributed in plant and fish oils. Since they cannot be made in the
   body from other substrates and must be supplied in food, they are
   called essential fatty acids. In the body, essential fatty acids are
   primarily used to produce hormone-like substances that regulate a wide
   range of functions, including blood pressure, blood clotting, blood
   lipid levels, the immune response, and the inflammation response to
   injury infection.

   Essential fatty acids are polyunsaturated fatty acids and are the
   parent compounds of the omega-6 and omega-3 fatty acid series,
   respectively. They are essential in the human diet because there is no
   synthetic mechanism for them. Humans can easily make saturated fatty
   acids or monounsaturated fatty acids with a double bond at the omega-9
   position, but do not have the enzymes necessary to introduce a double
   bond at the omega-3 or omega-6 position.

   The essential fatty acids are important in several human body systems,
   including the immune system and in blood pressure regulation, since
   they are used to make compounds such as prostaglandins. The brain has
   increased amounts of linolenic and alpha-linoleic acid derivatives.
   Changes in the levels and balance of these fatty acids due to a typical
   Western diet rich in omega-6 and poor in omega-3 fatty acids is alleged
   to be associated with depression and behavioral change, including
   violence. The actual connection, if any, is still under investigation.
   Further, changing to a more natural diet, or consumption of supplements
   to compensate for a dietary imbalance, has been associated with reduced
   violent behaviour and increased attention span, but the mechanisms for
   the effect are still unclear. So far, at least three human studies have
   shown results that support this: two school studies as well as a double
   blind study in a prison.

Trans fatty acids

   A trans fatty acid (commonly shortened to trans fat) is an unsaturated
   fatty acid molecule that contains a trans double bond between carbon
   atoms, which makes the molecule less 'kinked' in comparison to fatty
   acids with cis double bonds. These bonds are characteristically
   produced during industrial hydrogenation of plant oils. Research
   suggests that increasing amounts of trans fats are, for causal reasons
   not well understood, correlate with circulatory diseases such as
   atherosclerosis and coronary heart disease, than the same amount of
   non-trans fats.

Free fatty acids

   Fatty acids can be bound or attached to other molecules, such as in
   triglycerides or phospholipids. When they are not attached to other
   molecules, they are known as "free" fatty acids.

   The uncombined fatty acids or free fatty acids may come from the
   breakdown of a triglyceride into its components (fatty acids and
   glycerol).

   Free fatty acids are an important source of fuel for many tissues since
   they can yield relatively large quantities of ATP. Many cell types can
   use either glucose or fatty acids for this purpose. However, heart and
   skeletal muscle prefer fatty acids. On the other hand, the brain cannot
   use fatty acids as a source of fuel, relying instead on glucose, or on
   ketone bodies produced by the liver from fatty acid metabolism during
   starvation, or periods of low carbohydrate intake.

Fatty acids in dietary fats

   The following table gives the fatty acid and cholesterol composition of
   some common dietary fats.
                 Saturated Monounsaturated Polyunsaturated Cholesterol Vitamin E
                  g/100g       g/100g          g/100g        mg/100g    mg/100g
  Animal fats
  Lard                40.8            43.8             9.6          93      0.00
  Butter              54.0            19.8             2.6         230      2.00
  Vegetable fats
  Coconut oil         85.2             6.6             1.7           0       .66
  Palm oil            45.3            41.6             8.3           0     33.12
  Cottonseed oil      25.5            21.3            48.1           0     42.77
  Wheat germ oil      18.8            15.9            60.7           0    136.65
  Soya oil            14.5            23.2            56.5           0     16.29
  Olive oil           14.0            69.7            11.2           0      5.10
  Corn oil            12.7            24.7            57.8           0     17.24
  Sunflower oil       11.9            20.2            63.0           0     49.0
  Safflower oil       10.2            12.6            72.1           0     40.68
  Rapeseed oil         5.3            64.3            24.8           0     22.21

Acidity

   Short chain carboxylic acids such as formic acid and acetic acid are
   miscible with water and dissociate to form reasonably strong acids (
   pK[a] 3.77 and 4.76, respectively). Longer chain fatty acids do not
   show a great change in pK[a]. Nonanoic acid, for example, has a pK[a]
   of 4.96. However, as the chain length increases the solubility of the
   fatty acids in water decreases very rapidly, so that the longer chain
   fatty acids have very little effect on the pH of a solution. The
   significance of their pK[a] values therefore only has relevance to the
   types of reactions in which they can take part.

   Even those fatty acids that are insoluble in water will dissolve in
   warm ethanol, and can be titrated with sodium hydroxide solution using
   phenolphthalein as an indicator to a pale pink endpoint. This analysis
   is used to determine the free fatty acid content of fats, i.e. the
   proportion of the triglycerides that have been hydrolyzed.

Reaction of fatty acids

   Fatty acids react just like any other carboxylic acid, which means they
   can undergo esterification and acid-base reactions. Reduction of fatty
   acids yields fatty alcohols. Unsaturated fatty acids can additionally
   undergo addition reactions, most commonly hydrogenation, which is used
   to convert vegetable oils into margarine. With partial hydrogenation,
   unsaturated fatty acids can be isomerized from cis to trans
   configuration.

Auto-oxidation and rancidity

   Fatty acids at room temperature undergo a chemical change known as
   auto-oxidation. The fatty acid breaks down into hydrocarbons, ketones,
   aldehydes, and smaller amounts of epoxides and alcohols. Heavy metals
   present at low levels in fats and oils promote auto-oxidation. Fats and
   oils often are treated with chelating agents such as citric acid.
   Retrieved from " http://en.wikipedia.org/wiki/Fatty_acid"
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