This is the translation of an article that you will find in the Encyclopedia of the Académie d'agriculture de France :
Lecithins
Many food products
contain "lecithins", but what are they?
Food products from
the industry sometimes display "lecithins" on the
packaging, but what is this ingredient, listed by the European
classification of additives under the number E322?
Here a review of the
chemical history of food compounds will show us that the regulations
would benefit from being more in line with the definitions given
internationally by chemists.
About lecithin,
there is the same question as with the term "chlorophyll",
which was initially introduced by chemists to designate the green
material that can be extracted from green plants... before it was
discovered that it was actually a variable mixture of many compounds.
Having understood
that this green material was made of many green, blue, yellow, orange
and red pigments, chemists decided internationally to reserve the
name "chlorophylls" (in the plural) for particular
pigments, and more particularly for green pigments with a very
particular molecular structure.
The same historical
sequence can be found with many animal and plant materials. For
example, still following the work of chemists (in this case from the
18th century), the material isolated from egg white by evaporation of
water was called "albumin" for a long time, before the
progress of chemistry made it possible to understand that it was a
variable mixture, which led to the use of the word "albumins"
(in the plural), to designate particular proteins
Lecithin ? No,
lecithinS
For lecithins, they
were discovered in 1845 by the French chemist Theodore Nicolas Gobley
(1811-1876), who succeeded in extracting it from egg yolk. He created
the name from the Greek lekythos, which means "egg yolk",
and this definition persisted until 1850. The chemical nature of
lecithin remained unknown until 1874. Then the progress of chemistry
clarified the composition of the material isolated by Gobley, which
was in fact a mixture of several compounds.
Where the cacophony
sets in - and this is the breeding ground for fraud, dishonesty,
misunderstandings, etc. - is that technical or technological
publications have not kept up with the progress of chemistry, and
that one finds various definitions in these circles.
For example, some
have defined the product marketed under the name of lecithin as "a
mixture composed of polar lipids (glycolipids, phospholipids) and
triglycerides, obtained from animal or plant tissues" (we will
see later that these are the compounds). Others have designated under
this name "lipids containing phosphorus, extracted from eggs or
brain tissue". And a third definition refers to
phosphatidylcholine. According to the International Lecithin &
Phospholipids Society (ILPS, 2020), lecithin is "a complex
mixture of glycerophospholipids of plant, animal, or microbial
origin, containing varying amounts of triglycerides, fatty acids,
glycolipids, sterols, and sphingophospholipids. "Recently,
one researcher (Leonard, 2017) even provided his own definition,
naming lecithin "a group of lipid substances found in animal or
plant tissues that are essential for cell function."
In less
technological texts, we find other definitions. For example, in the
Encyclopedia Britannica (2020), we find the third of the
previous definitions, but also as a "natural" mixture
containing notable proportions of phosphatidylcholine (PC), cephalin
(phosphatidylethanolamine, PE) and phosphatidylinositol (PI).
Towards the same
clear definition for all
All this should be
swept away, because the 1905 law on the food trade imposes healthy,
marketable and... fair products: horse is not beef! However, fairness
imposes a single, common definition... which has moreover been given
very clearly by the International Union of Pure and Applied
Chemistry (IUPAC): for chemists around the world, lecithins are
"cholic esters of phosphatidic acids" (IUPAC, 2019). Since
chemists introduced the word "lecithin," they are the ones
with the definition, right?
To understand what
it means, let's start by analyzing the following representation, of a
phosphatidic acid molecule:
On such a
representation, the vertices carry carbon atoms, the letters O, H, P
indicate oxygen, hydrogen and phosphorus atoms respectively, the
segments represent bonds between atoms, and many hydrogen atoms are
omitted for clarity (and we know that there are enough of them for
each carbon atom to have a total of four bonds). That leaves R1 and
R2, which we will consider later, but, before that, let's observe
that, in the center of this structure, we find the following:
Here, we have
replaced the eliminated parts with hydrogen atoms (H)... and we find
the glycerol molecule, a "sugar" with three carbon atoms.
In the phosphatidic
acid molecule, we also find the phosphorus atom with its neighbors,
which corresponds to a phosphoric acid residue. Finally, the "R1"
and "R2" designate chains of carbon atoms linked to
hydrogen atoms; together with the doubly linked oxygen atoms, this
makes "fatty acids"... but as there are missing atoms, lost
during the assembly of the complete molecule, we should rather speak
of "fatty acid residues". In lecithins, fatty acid residues
have between 6 and 26 carbon atoms, depending on the source:
lecithins of animal origin have longer fatty acid residues, while the
number of carbon atoms is limited to about 20 for lecithins of
vegetable origin.
Finally, we
mentioned "cholic" esters of phosphatidic acids, which
means that lecithins contain a residue of a compound called
"choline":
Here, the letter N
represents a nitrogen atom.
And for the complete
lecithins, the molecules are :
Commercial names
to be revised
We have seen that
there is no ambiguity in the chemistry of lecithins... and this must
quickly change the vocabulary of the industrial world. Can we really
admit that this world designates under the name of lecithin mixtures
of phospholipids, but also of glycolipids, triglycerides, water and
sugars?
Glycolipids have
nothing to do with "cholic esters of phosphatidic acid":
they are compounds whose molecules include a lipidic part and a small
sugar. In the lipid part, two fatty acid residues are attached to a
glycerol residue, while the sugar residue is often a D-glucose,
D-galactose or inositol residue. Like phospholipids, these compounds
are present in cell membranes. The sugars leave the phospholipid
bilayer, in the aqueous solutions that bound the cell membranes.
Glycolipids are found in plant and animal tissues, but are most
abundant in photosynthesizing algae and plants.
Triglycerides, on
the other hand, have nothing to do with "cholic esters of
phosphatidic acid" either: they are the compounds that make up
oils, with a glycerol residue linked to three fatty acid residues.
By the way, why
do food products contain lecithins?
Now that we know
what lecithins really are, let's examine their usefulness by first
considering the case of chocolate making. Let's skip the roasting of
the cocoa seeds, the pressing of the roasted seeds, to produce cocoa
butter, and focus on the "conching" stage, where sugar is
added to this cocoa butter with vegetable matter added. This is
traditionally done in a heated millstone, which rotates until the
beans are reduced to very small particles, smaller than the 15
thousandths of a millimeter that remain perceptible between the
teeth. When the millstone turns like this, in the mixture, it
struggles, and consumes a considerable amount of energy, especially
because the grains of sugar are surrounded by a thin layer of
water... which does not mix well with the melted fat. As soon as
lecithins are added to the mixture, the effect is seen: the grinding
wheel starts to turn more easily, the rotation being facilitated,
because the lecithins favour the contact of the fat and the water.
In various food
products, too, lecithins have this "surfactant" role,
allowing to reduce the energy necessary for the dispersion of fat, in
the form of droplets, in an aqueous solution or conversely. Think of
the famous mayonnaise sauce, where the egg yolk provides both water
and lecithins, and where oil is dispersed and added drop by drop
(although, in this case, the proteins also provided by the egg yolk
are much more active than lecithins).
Are these lecithins
used by the food industry "dangerous", as some of those who
criticize "additives" claim? The first answer is that
lecithins are present in the cells of our body: these cells are
limited by a "membrane", which is a double layer of
phospholipids or glycolipids. Eating meat, fish, vegetables or fruit
means consuming lecithins en masse, even without the slightest
intervention of an industry that some criticize for reasons that we
will not analyze here.
References
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