Further to Phil and Sadoun's recent postings, here's an extract from The
Olive Book (Canterbury University Press, 1999) by yours truly (and now being
reprinted!).

"Olive oil is mostly (98.5 to 99.5 percent) triglycerides ‹ molecules made
up of three fatty acids (long chain hydrocarbons with an acid "bit" on the
end) linked together by another molecule called glycerol. There are also
some of these fatty acids floating around without linking up with glycerol.
These are the free fatty acids, and they determine the overall acidity of
the oil. The majority of the fatty acids in olive oil have 18 carbon atoms
in their chain, and the single biggest component, oleic acid, has one double
bond in its chain ‹ making it a "monounsaturated" fatty acid. No double
bonds and the fatty acid is "saturated", more than one and it¹s
"polyunsaturated".

Oleic acid makes up between 55 and 83 percent of the oil The next most
common fatty acid is linoleic acid at between 3.5 and 21 percent. It also
has 18 carbon atoms, but two double bonds, and so is a polyunsaturate. The
"next" acid in the sequence, linolenic acid, has three double bonds, but is
usually present at levels of under one percent. Both of these last two acids
are important because they supply the chemical precursors for a group of
hormones called the prostaglandins. These are used by the body to control a
huge variety of functions, including things like sex, inflammation, blood
pressure and blood clotting.

Other fatty acids present in olive oil include palmitic acid (7.5% to 20%,
16 carbon atoms, no double bonds, in shorthand 16:0), which is the
predominant saturated fat in the oil, palmitoleic (0.3%-3.5%, 16:1), and
stearic acid (0.5%-5.0%, 18:0). There are seven others, but all appear in
very low concentrations.

The rest of the oil ‹ the 0.5 to 1.5 percent that isn¹t triglycerides or
free fatty acids, is made up of a mixture of pigments, antioxidants and
volatile and aroma compounds. The pigments are principally chlorophyll,
which is green, and carotene, which is red, and mixtures of the two give oil
its characteristic range of colours. The antioxidants, manly tocopherols and
polyphenols are very important, as we¹ll see, and include oleuropein, the
bitter substance that gradually disappears as fruits ripen. The aroma
compounds may be present in very small amounts, but add greatly to the
flavour content of the oil. Any refining process gets rid of these."

The IOOC has a "standard" for the levels of the various constituents of oil
quoted by Guido. If anyone really wants it, I'll dig it out and post it...

--
Gareth Renowden, Limestone Hills, New Zealand
Words, olives and truffles
Office +64 (0)3 355 9552 Home +64 (0)3 314 9921
Mobile 025 790 070
"I knew she carried a snorkel in her handbag, but would she use it?"(Sir
Henry)