Tag Archives: unsaturated fatty acids

Chemical composition of olive oil

Chemical composition of olive oil: contents in brief

Olive oil constituents

Olive Oil
Fig. 1 – EVOO

From a chemical point of view, we can identify in the olive oil two fractions, depending on the behavior in the presence of heating and strong alkaline solutions (concentrated solutions of KOH or NaOH):

  • the saponifiable fraction, which represents 98-99% of the total weight, is composed of substances that form soaps in the above conditions;
  • the unsaponifiable fraction, which represents the remaining 1-2% of the total weight, is composed of substances that fail to form soaps in the above conditions.

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Saponifiable fraction of olive oil

It is composed of saturated and unsaturated fatty acids, esterified almost entirely to glycerol to form triglycerides (or triacylglycerols). To a much lesser extent, diglycerides (or diacylglycerols), monoglycerides (monoacylglycerols), and free fatty acids are also found.
Unsaturated fatty acids make up 75 to 85% of the total fatty acids. Oleic (O) and linoleic (L) acids are the most abundant ones; palmitoleic, eptadecenoic, gadoleic and alpha-linolenic (Ln) acids are present in lower/trace amounts.

Oleic Acid
Fig. 2 – IOOC and Fatty Acids

Oleic acid is the major fatty acid in olive oils. According to the rules laid down by the International Olive Oil Council (IOOC), its concentration must range from 55% to 83% of total fatty acids.
Linoleic acid is the most abundant polyunsaturated fatty acid in olive oil; its concentration must vary between 2.5% and 21% (IOOC). Because of its high degree of unsaturation, it is subject to oxidation; this means that an oil high in linoleic acid becomes rancid easily, and thus it may be stored for a shorter time.
In a Mediterranean-type diet, olive oil is the main source of fat: therefore, oleic acid, among monounsaturated fatty acids, and linoleic acid, among polyunsaturated fatty acids, are the most abundant fatty acids.
alpha-Linolenic acid must be present in very low amount, according to the IOOC standards ≤1%. It is an omega-3 polyunsaturated fatty acid, which may have health benefits. However, because of to its high degree of unsaturation (higher than that of linoleic acid), it is very susceptible to oxidation, and therefore it promotes rancidity of the olive oil that contains it.
Saturated fatty acids make up 15 to 25% of the total fatty acids.
Palmitic (P) (7.5-20%) and stearic (S) acids (0.5-5%) are the most abundant saturated fatty acids; myristic, heptadecanoic, arachidic, behenic and lignoceric acids may be present in trace amounts.

The presence of fatty acids that should be absent or present in amounts different than those found is a marker of adulteration with other vegetable oils. On this regard, particular attention is paid to myristic, arachidic, behenic, lignoceric, gadoleic and alpha-linolenic acids, whose limits are set by IOOC.

Fatty acid composition is influenced by several factors.

  • The climate.
  • The latitude.
  • The zone of production.
    Italian, Spanish and Greek olive oils are high in oleic acid and low in palmitic and linoleic acids, while Tunisian olive oils are high in palmitic and linoleic acids but lower in oleic acid. Therefore, oils can be divided into two groups:

one rich in oleic acid and low in palmitic and linoleic acids;
the other high in palmitic and linoleic acids and low in oleic acid.

  • The cultivar.
  • The degree of olive ripeness at the time of oil extraction.
    It should be noted that oleic acid is formed first in the fruit, and data seem to indicate a competitive relationship between oleic acid and palmitic, palmitoleic, and linoleic acids.

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Triglycerides of olive oil

Olive Oil
Fig. 3 – The sn Positions of Triglycerides

As previously said, fatty acids in olive oil are almost entirely present as triglycerides.
In small percentage, they are also present as diglycerides, monoglycerides, and in free form.
During triglyceride biosynthesis, thanks to the presence of specific enzymes, only about 2% of glycerol binds palmitic acid in the sn-2 position (also the percentage of stearic acid in the sn-2 position is very low); for the most part, the sn-2 position is occupied by oleic acid.
On the contrary, if we consider oils that have undergone a nonenzymatic esterification, the percentage of palmitic acid in the sn-2 position increases significantly.
Note: sn = stereospecific numbering

Among triglycerides present in significant proportions in olive oil, there are:

  • OOO: 40-59%;
  • POO: 12-20%;
  • OOL: 12.5-20%;
  • POL:  5.5-7%;
  • SOO: 3- 7%.

POP, POS, OLnL, OLnO, PLL, PLnO are present in smaller amounts.
Trilinolein (LLL) is a triglyceride that contains three molecules of linoleic acid. Its low content is an indicator of an oil of good quality.
Triglycerides containing three saturated fatty acids or three molecules of alpha-linolenic acid have not been reported.

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Diglycerides and monoglycerides of olive oil

Their presence is due to an incomplete synthesis and/or a partial hydrolysis of triglycerides.
The content of diglycerides in virgin olive oil ranges from 1% to 2.8%. 1,2-Diglycerides prevail in fresh olive oil, representing over 80% of the diglycerides. During oil storage, isomerization occurs with a progressive increase of the more stable 1-3 isomers, which after about 10 months become the major isomers.
Therefore, the ratio 1,2/1,3-diglycerides may be used as an indicator of the age of the oil.
Monoglycerides are present in amounts lower than diglycerides, <0.25%, with 1-monoglycerides far more abundant than 2-monoglycerides.

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Unsaponifiable fractions of olive oil

It is composed of a large number of different molecules, very important from a nutritional point of view, as they contribute significantly to the health effects of olive oil.
Furthermore, they are responsible for the stability and the taste of olive oil, and are also used to detect adulteration with other vegetable oils.
This fraction includes tocopherols, sterols, polyphenols, pigments, hydrocarbons, aromatic and aliphatic alcohol, triterpene acids, waxes, and minor constituents.
Their content is influenced by factors similar to those seen for fatty acid composition, such as:

  • the cultivar;
  • the degree of ripeness of the olive;
  • the zone of production;
  • the crop year and olive harvesting practices;
  • the storage time of olives;
  • the oil extraction process;
  • the storage conditions of the oil.

It should be noted that many of these compounds are not present in refined olive oils, as they are removed during the refining processes.

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Polyphenols

They make up 18 to 37% of the unsaponifiable fraction.
They are a very heterogeneous group of molecules with nutritional and organoleptic properties  (for example, oleuropein and hydroxytyrosol give oil its bitter and pungent taste).
For a more extensive discussion, see: ” Polyphenols in olive oil: variability and composition.”

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Hydrocarbons

Olive Oil
Fig. 4 – Squalene

They make up 30 to 50% of the unsaponifiable fraction.
Squalene and beta-carotene are the main molecules.
Squalene, isolated for the first time from shark liver, is the major constituent of the unsaponifiable fraction, and constitutes more than 90% of the hydrocarbons. Its concentration ranges from 200 to 7500 mg/kg of olive oil.
It is an intermediate in the biosynthesis of the four-ring structure of steroids, and it seems to be responsible of several health effects of olive oil.
In the hydrocarbon fraction of virgin olive oil, n-paraffins, diterpene and triterpene hydrocarbons, isoprenoidal polyolefins are also found.
Beta-carotene acts both as antioxidant, protecting oil during storage, and as dye (see below).

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Sterols

They are important lipids of olive oil, and are:

  • linked to many health benefits for consumers;
  • important to the quality of the oil;
  • widely used for checking its genuineness.
    On this regard, it is to underline that sterols are species-specific molecules; for example, the presence of high concentrations of brassicasterol, a sterol typically found in Brassicaceae (Cruciferae) family, such as rapeseed, indicates adulteration of olive oil with canola oil.

Four classes of sterols are present in olive oil: common sterols, 4-methylsterols, triterpene alcohols, and triterpene dialcohols. Their content ranges from 1000 mg/kg, the minimum value required by the IOOC standard, to 2000 mg/kg. The lowest values are found in refined oils because of the refining processes may cause losses up to 25%.

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Common sterols or 4α-desmethylsterols
Olive Oil
Fig. 5 – beta-Sitosterol

Common sterols are present mainly in the free and esterified form; however they have been also found as lipoproteins and sterylglucosides.
The main molecules are beta-sitosterol, which makes up 75 to 90% of the total sterol, Δ5-avenasterol, 5 to  20%, and campesterol, 4%. Other components found in lower amounts or traces are, for example, stigmasterol, 2%, cholesterol, brassicasterol, and ergosterol.

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4-Methylsterols

They are intermediates in the biosynthesis of sterols, and are present both in the free and esterified form. They are present in small amounts, much lower than those of common sterols and triterpene alcohols, varying between 50 and 360 mg/kg. The main molecules are obtusifoliol, cycloeucalenol, citrostadienol, and gramisterol.

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Triterpene alcohols or 4,4-dimethylsterols

They are a complex class of sterols, present both in the free and esterified form. They are found in amounts ranging from 350 to 1500 mg/kg.
The main components are beta-amyrin, 24-methylenecycloartanol, cycloartenol, and butyrospermol; other molecules present in lower/trace amounts are, for example, cyclosadol, cyclobranol, germanicol, and dammaradienol.

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Triterpene dialcohols

The main triterpene dialcohols found in olive oil are erythrodiol and uvaol.
Erythrodiol is present both in the free and esterified form; in virgin olive oil, its level varies between 19 and 69 mg/kg, and the free form is generally lower than 50 mg/kg.

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Tocopherols

They make up 2 to 3% of the unsaponifiable fraction, and include vitamin E.
Of the eight E-vitamers, alpha-tocopherol represents about 90% of tocopherols in virgin olive oil. It is present in the free form and in very variable amount, but on average higher than 100 mg/kg of olive oil. Thanks to its in vivo antioxidant properties, its presence is a protective factor for health. Alpha-tocopherol concentration seems to be related to the high levels of chlorophylls and to the concomitant requirement for deactivation of singlet oxygen.
Beta-tocopherol, delta-tocopherol, and gamma-tocopherol are usually present in low amounts.

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Pigments

In this group we find chlorophylls and carotenoids.
In olive oil, chlorophylls are present as phaeophytins, mainly  phaeophytin a (i.e. a chlorophyll from which magnesium has been removed and substituted with two hydrogen ions), and confer the characteristic green color to olive oil. They are photosensitizer molecules that contribute to the photooxidation of olive oil itself.
Beta-carotene and lutein are the main carotenoids in olive oil. Several xanthophylls are also present, such as antheraxanthin, beta-cryptoxanthin, luteoxanthin, mutatoxanthin, neoxanthin, and violaxanthin.
Olive oil’s color is the result of the presence of chlorophylls and carotenoids and of their green and yellow hues. Their presence is closely related.

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Triterpene acids

They are important components of the olive, and are present in trace amounts in the oil.
Oleanolic and maslinic acids are the main triterpene acids in virgin olive oil: they are present in the olive husk, from which they are extracted in small amount during processing.

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Aliphatic and aromatic alcohols

Fatty alcohols and diterpene alcohols are the most important ones.
Aliphatic alcohols have a number of carbon atoms between 20 and 30, and are located mostly inside the olive stones, from where they are partially extracted by milling.

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Fatty alcohols

They are linear saturated alcohols with more than 16 carbon atoms.
They are found in the free and esterified form and are present, in virgin olive oil, in amount not generally higher than 250 mg/kg.
Docosanol (C22), tetracosanol (C24), hexacosanol (C26), and octacosanol (C28) are the main fatty alcohols in olive oil, with tetracosanol and hexacosanol present in larger amounts.
Waxes, which are minor constituents of olive oil, are esters of fatty alcohols with fatty acids, mainly of palmitic acid and oleic acid. They can be used as a criterion to discriminate between different types of oils; for example, they must be present in virgin and extra virgin olive oil at levels <150 mg/kg, according to the IOOC standards.

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Diterpene alcohols

Geranylgeraniol and phytol are two acyclic diterpene alcohols, present in the free and esterified form. Among esters present in the wax fraction of extra virgin olive oil, oleate, eicosenoate , eicosanoate, docosanoate, and tetracosanoate have been found, mainly as phytyl derivatives.

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Volatile compounds

More than 280 volatile compounds have been identified in olive oil, such as hydrocarbons, the most abundant fraction, alcohols, aldehydes, ketones, esters, acids, ethers and many others. However, only about 70 of them are present at levels higher than the perception threshold beyond which they may contribute to the aroma of virgin olive oil.

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Minor components

Phospholipids are found among the minor components of olive oil; the main ones are phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol.
In the unfiltered oils, trace amounts of proteins may be found.

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References

Gunstone F.D. Vegetable oils in food technology: composition, properties and uses. 2th Edition. Wiley J. & Sons, Inc., Publication, 2011

Pasqualone A., Sikorska E., Gomes T. Influence of the exposure to light on extra virgin olive oil quality during storage. Eur Food Res Technol 2005;221:92-8. doi:10.1007/s00217-004-1126-8

Servili M., Sordini B., Esposto S., Urbani S., Veneziani G., Di Maio I., Selvaggini R. and Taticchi A. Biological activities of phenolic compounds of extra virgin olive oil. Antioxidants 2014;3:1-23. doi:10.3390/antiox3010001

Dietary trans fatty acids: industrial and natural sources

Industrial and natural sources of dietary trans fatty acids

Dietary trans fatty acids come from different sources:

  • they can come from industrial processing, being the by-product of partial hydrogenation of unsaturated vegetable oils;
  • they can be produced naturally by plants and animals.

Dietary trans fatty acids from partial hydrogenation of vegetable oils

Dietary Trans Fatty Acids: Hydrogenation Process
Fig. 1 – Hydrogenation of Oleic Acid

In industrialized countries, greater part of the consumed trans fatty acids are produced industrially (in USA about 80%), in varying amounts, during partial hydrogenation of edible oils containing unsaturated fatty acids.
Hydrogenate means to add hydrogen atoms to unsaturated sites (that is, on a double bond) on the carbon chains of fatty acids by heating vegetable oils in presence of metal catalyst and hydrogen.
During the partial hydrogenation, an incomplete saturation of the unsaturated sites on the carbon chains of unsaturated fatty acids occurs: some double bonds remain, but they may be moved in their positions on the carbon chain, producing geometrical and positional isomers (double bonds are modified in both conformation and position).
Notably, with regard to fish oil, trans fatty acid content in non-hydrogenated oils and in highly hydrogenated oils is 0,5 and 3,6%, whereas in partially hydrogenated oils is 30%.
Hydrogenation converts vegetable oils into semisolid fats for use in:

  • margarines and shortenings;
  • commercial cooking;
  • manufacturing processes.

It should be noted that partial hydrogenation largely destroys alpha-linolenic acid, the plant-based omega-3-fatty acid.
Industrial trans fatty acids (ITFA) have adverse effects on:

  • serum lipid levels (total and LDL-cholesterol);
  • endothelial cells;
  • systemic inflammation;
  • other risk factors for cardiovascular disease;
  • moreover, they are positively associated with the risk of coronary heart disease (CHD), and sudden death from cardiac causes and diabetes.

Industrial trans fatty acids are an independent cardiovascular risk factor.
Their adverse effects are seen at low level of intake: for a person consuming 2000 kcal/d, 20-60 kcal from industrial trans fatty acids, equivalent to about 2-7 g or 1-3% of the total energy intake, is enough.
So, avoidance of industrial trans fatty acids, or a consumption of less 0,5% of total daily energy intake is necessary to avoid their adverse effects (these are far stronger, on average, than those of food contaminants or pesticide residues!).

Dietary trans fatty acids from deodorization of vegetable oils

Very small amounts of trans fatty acids (less than 2 percent) are formed during deodorization of vegetable oils, a process unrelated to partial hydrogenation and necessary in the refining of edible oils. During this process trans fatty acids with more than one double bond are formed in small amounts (if the isomer contains 18 carbon atoms it is marked C18:2). These isomers are also present in fried foods and in considerable amounts in partially hydrogenated vegetable oils (e.g. soybean oil).

Dietary trans fatty acids from animals

A natural source comes from bacterial transformation of a proportion of the relatively small amounts of unsaturated fatty acids ingested by ruminants in their rumen.
They are present at low levels in meat and full fat dairy products from cows, sheep, and other ruminants (typically <5% of total fatty acids).

Dietary trans fatty acids from vegetables

Another natural source is represented by some plant species, and plant-derived foods as:

  • leeks, peas, lettuce and spinach, that contain trans-3-hexadecenoic acid;
  • rapeseed oil, that contains brassidic acid and gondoic acid.

In these sources trans fatty acids are present in small amounts.

“Homemade”dietary trans fatty acids

They are produced at home during frying with vegetable oils.

Isomers of dietary trans fatty acids

Dietary Trans Fatty Acids: ITFA
Fig. 2 – ITFA

The most important cluster of trans fatty acids both animal and industrial origin is isomers containing 18 carbon atoms  plus one double bond (C18:1) whose position varies between the Δ6 and Δ16 carbon atoms of molecule.
Even if the same trans fatty acids are largely present in industrial trans fatty acids and in trans fatty acids from ruminants, there is a considerable quantitative difference between individual molecules in the two different sources.
The most common isomers in both sources are those with double bond in position between Δ9 and Δ11, but Δ11-C18:1 or vaccenic acid represents over 60% of the trans C18:1 isomers in ruminant trans fatty acids, whereas in industrial ones  Δ9-C18:1 or elaidic acid comprises 15-20%, and Δ10-C18:1 and Δ11-C18:1 over 20% each others.

References

Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

Lemaitre R.N., King I.B., Raghunathan T.E. et al. Cell membrane trans-fatty acids and the risk of primary cardiac arrest. Circulation 2002;105:697-01 [Abstract]

Lichtenstein A. H., Ausman L., Jalbert S.M , Schaefer E.J. Effect of different forms of dietary hydrogenated fats on serum lipoprotein cholesterol levels. N Engl J Med 1999;340:1933-40 [Abstract]

Lopez-Garcia E., Schulze M.B., Meigs J.B., Manson JA.E, Rifai N., Stampfer M.J., Willett W.C. and Hu F.B. Consumption of trans fatty acids is related to plasma biomarkers of inflammation and endothelial dysfunction. J Nutr 2005;135:562-66 [Abstract]

Mozaffarian D. Commentary: Ruminant trans fatty acids and coronary heart disease-cause for concern? Int J Epidemiol 2008;37:182-84 [Extract]

Mozaffarian D., Katan M.B., Ascherio A., Stampfer M.J., Willett W.C. Trans fatty acids and cardiovascular disease. N Engl J Med 2006;354:1601-13 [Abstract]

Oomen C.M., Ocke M.C., Feskens E.J., van Erp-Baart M.A., Kok F.J., Kromhout D. Association between trans fatty acid intake and 10-year risk of coronary heart disease in the Zutphen Elderly Study: a prospective population-based study. The Lancet 2001;357:746-51 [Abstract]

Willett W. and Mozaffarian D. Ruminant or industrial sources of trans fatty acids: public health issue or food label skirmish? Am J Clin Nutr 2008;87:515-6 [PDF]

Trans fatty acids: definition and chemistry

What are trans fatty acids?

Trans fatty acids (TFA) or partially hydrogenated fatty acids are unsaturated fatty acids, a class of lipids, with at least one a double bond in the trans configuration.
They may result from:

In industrialized countries, the greater part of the consumed trans fatty acids are produced industrially, in varying amounts, during partial hydrogenation of edible oils containing monounsaturated and polyunsaturated fatty acids.
Note: partially hydrogenated vegetable oils were developed in the United States in 1903 as a cheaper alternative to animal fats.

While ruminant trans fatty acids, in amounts actually consumed in diets, are not harmful for human health, consumption of industrial partially hydrogenated fatty acids has neither apparent benefit nor intrinsic value, above their caloric contribution: from human health standpoint they are only harmful.

Chemical structure of trans fatty acids

Fatty acids

Fatty acids are made up by carbon (from the “smallest”, formic acid, containing only one carbon atom, up to fatty acids with over 30 carbon atoms), hydrogen and oxygen atoms linked to form a carboxylic group (the “hydrophilic head” of the molecule) that continues in a more or less long chain of carbon atoms linked each other by chemical bonds that may be single or double (the “hydrophobic tail”). Hydrogen atoms are linked to carbon and oxygen atoms.
Fatty acids are defined:

  • saturated, if chemical bonds between carbon atoms of the chain are all simple;
  • monounsaturated, if a double bond is present in the chain;
  • polyunsaturated, if two or more double bonds are present between single bonds of the chain.

Monounsaturated fatty acids and polyunsaturated fatty acids can be defined as unsaturated.

Cis and trans isomers

Trans Fatty Acids
Fig. 1 – Cis and Trans Isomers

Carbon-carbon double bonds show planar conformation and so they can be considered as plans whose opposite sides carbon chain attaches and continues.
“The entry” and “the exit” of the carbon chain from the plain may occur on the same side of the plan, and in this case double bond is defined in cis configuration, or on opposite side, and in that case it is defined in trans configuration.
Unsaturated fatty acids most commonly have their double bonds in cis configuration; the other, less common, configuration is trans.
Unsaturated fatty acids with at least one double bond in trans configuration are called trans fatty acids.
Cis bond causes a bend in the fatty acids chain, whereas the geometry of trans bond straightens the fatty acid chain, imparting a structure more similar to that of saturated fatty acids.
Bent molecules can’t pack together easily but linear ones can do it and this gives the fats in which they are a higher melting point. Heightening the melting point of fats means that it is possible to convert them from liquid form to semi-solids and solids; for this reason fats containing a greater part of saturated fatty acids, or the geometrically similar partially hydrogenated fatty acids, are solid at room temperature (partially hydrogenated fatty acids tend to be less solid than saturated fats).

In industrially trans fatty acids-containing fats, cyclic monomers as well as intramolecular linear dimmers are also present.

References

Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Ascherio A., Katan M.B., Zock P.L., Stampfer M.J., Willett W.C. Trans fatty acids and coronary heart disease. N Engl J Med 1999;340:1994-8 [Abstract]

 Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

Mozaffarian D. Commentary: Ruminant trans fatty acids and coronary heart disease-cause for concern? Int J Epidemiol 2008;37:182-84 [Extract]

Mozaffarian D., Katan M.B., Ascherio A., Stampfer M.J., Willett W.C. Trans fatty acids and cardiovascular disease. N Engl J Med 2006;354:1601-13 [Abstract]

Stender S., Dyerberg J. The influence of trans fatty acids on health. Fourth edition 2003 (from Danish Nutrition Council; publ. no. 34)

Willett W. and Mozaffarian D. Ruminant or industrial sources of trans fatty acids: public health issue or food label skirmish? Am J Clin Nutr 2008;87:515-6 [PDF]

Artificial trans fats: businness and health

The hydrogenation of vegetable oils

The process of hydrogenation was first discovered in 1897 by French Nobel prize in Chemistry (jointly with fellow Frenchman Victor Grignard) Paul Sabatier using a nickel catalyst.
Partially hydrogenated vegetable oils were developed in 1903 by a German chemist, Wilhelm Normann who files British patent on “Process for converting unsaturated fatty acids or their glycerides into saturated compounds” and the term trans fatty acids or trans fats (they are produced  during partial hydrogenation of edible oils containing monounsaturated and polyunsaturated fatty acids) appeared for the first time in the Remark column of the 5th edition of the “Standard Tables of Food Composition” in Japan.

Partially hydrogenated vegetable oils were developed as a cheaper alternative to animal fats.
Moreover, they:

  • contribute to the hardness of fat in which they are who can be semi-solids and solids (they are used to make margarine or shortening with a melting point, consistency and “mouth feel” similar to those of butter);
  • have a long shelf life at room temperature;
  • have flavor stability and be stable during frying.

Note: per year in USA 6-8 billion pounds of hydrogenated vegetable oil are produced.

The war on artificial trans fats

Trans Fats
Fig. 1 – Shortening

The first hydrogenated oil was cottonseed oil in USA in 1911 to produce vegetable shortening.
So, before this date, the only trans fats in human diet were those derived from ruminants.
In the 1930’s partial hydrogenation became popular with the development of margarine; through hydrogenation, oils such as soybean, safflower and cottonseed oil, which are rich in unsaturated fatty acids, are converted to margarines and vegetable shortenings.
Until 1985 no adverse effects of trans fats on human health was demonstrated and in 1975 Procter & Gamble study shows no effect of partially hydrogenated fats on cholesterol.
Their use in fast food preparation grow up from 1980’s when the role of dietary saturated fats in increasing cardiac risk began clear; it was led a successful campaign to get McDonald’s to switch from beef tallow to vegetable oil for frying its French fries. Meanwhile, studies began to raise concerns about their effects on health: on 1985 in USA Food and Drug Administration (FDA) concludes that trans fats and monounsaturated fat oleic acid affect serum cholesterol level similarly but from the second half of 1985 their harmful began clear and the final proof comes from both controlled feeding trials and prospective epidemiologic studies.
After June 1996 they were eliminated from margarine sold in Australia, which before contributed about 50% of the dietary intake of trans fatty acids in such country.
On March 11, 2003 the Danish government, after a debate started in 1994 and two new reports in 2001 and 2003, decided to phase out the use of industrially produced trans fats (ITFA) in food before the end of 2003; two years later, however, the European Commission asked Denmark to withdraw this law, which was not accepted on the EU level, unfortunately.
Canada is considering legislation to eliminate industrially produced trans fats from food supplies.
On 2003 FDA ruled that food labels (for conventional foods and supplements) show trans fat content beginning January 1, 2006. Notably, this ruling is the first substantive change to food labeling since the requirement for per-serving food labels information was added in 1990.
On 2005 the US Department of Agriculture made a minimized intake of trans fats a key recommendation of the new food-pyramid guidelines.
On 2006 American Heart Association recommends to limit their intake to 1% of daily calorie consumption and suggests food manufacturers and restaurants switch to other fats.
On 2006 New York City Board of Health announces trans fat ban in its 40.000 restaurants within July 1, 2008.

References

Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Ascherio A., Katan M.B., Zock P.L., Stampfer M.J., Willett W.C. Trans fatty acids and coronary heart disease. N Engl J Med 1999;340:1994-8 [Abstract]

Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

Eckel R.H., Borra S., Lichtenstein A.H., Yin-Piazza D.Y. Understanding the Complexity of Trans fatty acid reduction in the American diet. American Heart Association trans fat conference 2006 report of the trans fat conference planning group. Circulation 2007;115:2231-46; originally published online Apr 10, 2007 [Abstract]

Mozaffarian D., Jacobson M.F., Greenstein J.S. Food Reformulations to reduce trans fatty acids. N Eng J Med 2010;362:2037-39 [PDF]

Okie S. New York to trans fats: you’re out! N Engl J Med 2007;356:2017-21 [PDF]

Stender S., Astrup A., Dyerberg J. What went in when trans went out?. N Engl J Med 2009;361:314-16 [PDF]

Stender S., Dyerberg J. and Astrup A. Consumer protection through a legislative ban on industrially produced trans fatty acids in foods in Denmark. Scand J Food Nutr 2006;50:155-60 [Abstract]

Stender S., Dyerberg J. The influence of trans fatty acids on health. Fourth edition 2003 (from Danish Nutrition Council; publ. no. 34)

Long chain fatty acid synthesis

Fatty acid synthesis

Fatty Acid Synthesis
Fig. 1 – Long Chain Fatty Acids

When excess calories are consumed from carbohydrates or proteins, such surplus is used to synthesize fatty acids and then triacylglycerols, while it doesn’t occur if the excess come from fats.

De novo fatty acid synthesis in plants and animals

De novo fatty acid synthesis is largely similar among plants and animals.
It occurs in chloroplasts of photosynthetic cells of higher plants, and in cytosol of animal cells by the concerted action of two enzymes: acetyl CoA carboxylase and fatty acid synthase.
Fatty acid synthase is a multienzyme complex that catalyzes a repeating four-step sequence by which the fatty acyl chain is extended by two carbons, at the carboxyl end, every each passage through the cycle; this four-step process is the same in all organisms.
In animals, the primary site for lipid metabolism is liver, not the adipose tissue.  However, adipose tissue is  a major organ system in which fatty acid synthesis occurs, though in humans it is less active than in many other animal species.

Fatty Acid Synthesis
Fig. 2 – Palmitic Acid Synthesis

Although myristic, lauric and a trace of stearic acids may also be produced, in animals and plants the main product of these reactions is palmitic acid.
It should be noted that in certain plants, such as palm and coconut, chain termination occurs earlier than palmitic acid release: up to 90% of the fatty acids produced and then present in the oils of these plants are between 8 (caprylic acid) and 14 (myristic acid) carbons long (palmitic acid: 16 carbon atoms).

Synthesis of long chain saturated and unsaturated fatty acids

Fatty Acid Synthesis
Fig. 3 – Palmitic Acid Metabolism

Palmitic acid is the commonest saturated fatty acid in plant and animal lipids, but generally it is not present in very large proportions because it may be undergo into several metabolic pathways.
In fact:

  • it is the precursor of stearic acid;
  • it may be desaturated (insertion of a double bond into fatty acid chain) to palmitoleic acid, the precursor of all fatty acids of omega-7 or n-7 family, in a reaction catalyzed by Δ9-desaturase, an ubiquitous enzyme in both plant and animal kingdoms and the most active lipid enzyme in mammalian tissues, the same enzyme that catalyzes the desaturation of stearic acid to oleic acid (see below).
    Note: Δ9- desaturase inserts double bounds in the 9-10 position of the fatty acid carbon chain, position numbered from the carboxyl end of the molecule, and:

if the substrate is palmitic acid, the double bond will appear between n-7 and n-8 position of the chain (in this case numbered from the methyl end of the molecule), so producing palmitoleic acid, the founder of omega-7 series;
numbering-atoms-palmitic-acid

if the substrate is stearic acid, the double bond will appear between n-9 and n-10 position of the chain and oleic acid will be produced.
numbering-atoms-stearic-acid

  • It may be esterified into complex lipids.

Of course, in plants and animals there are fatty acids longer and/or more unsaturated than these just seen thanks to modification systems (again desaturation and elongation) that catalyze reactions of fatty acid synthesis that are organism- tissue- and cell- specific.

Fatty Acid Synthesis
Fig. 4 – Stearic Acid Metabolism

For example, stearic acid may be:

  • elongated to arachidic, behenic and lignoceric acids, all saturated fatty acids, in reactions catalyzed by elongases.
    Again, chain elongation occurs, both in mitochondria and in the smooth endoplasmic reticulum, by the addition of two carbon atom units at a time at the carboxylic end of the fatty acid through the action of fatty acid elongation systems (particularly long and very long saturated fatty acids, from 18 to 24 carbon atoms, are synthesized only on cytosolic face of the smooth endoplasmic reticulum);
  • desaturated, as seen, to oleic acid, an omega-9 or n-9 fatty acid, in a reaction catalyzed by Δ9-desaturase. Several researchers have postulated that the reason for which stearic acid is not hypercholesterolemic is its rapid conversion to oleic acid.
Fatty Acid Synthesis
Fig. 5 – Oleic Acid Metabolism

Oleic acid is the start point for the synthesis of many other unsaturated fatty acids by reactions of elongation and/or desaturation.

In fact:

Omega-3 and omega-6 PUFA synthesis

Fatty Acid Synthesis
Fig. 6 – Omega-3 and Omega-6 Synthesis

Animal tissues can desaturate fatty acids in the 9-10 position of the chain, thanks to the presence of Δ9 desaturase; as previously seen, if the substrate of the reaction is palmitic acid, the double bond will appear between n-7 and n-8 position, with stearic acid between n-9 and n-10 position, so leading to formation respectively of palmitoleic acid and oleic acid.
Animals lack Δ12- and Δ15-desaturases, enzymes able to desaturate carbon carbon bonds beyond the 9-10 position of the chain. For these reason, they can’t produce de novo omega-3 and omega-6 PUFA (which have double bonds also beyond the 9-10 position), that are so essential fatty acids.
Δ12- and Δ15-desaturases are present in plants; though many land plants lack Δ15-desaturase, also called omega-3 desaturase, planktons and aquatic plants in colder water possess it and produce abundant amounts of the omega-3 fatty acids.

References

Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Bender D.A. “Benders’ dictionary of nutrition and food technology”. 2006, 8th Edition. Woodhead Publishing. Oxford

Burr G. and Burr M. A new deficiency disease produced by the rigid exclusion of fat from the diet. J Biol Chem 1929;82:345-67 [Full Text]

Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

Cozzani I. e Dainese E. “Biochimica degli alimenti e della nutrizione”. Piccin Editore, 2006

Rosenthal M.D., Glew R.H. Mediacal biochemistry. Human metabolism in health and disease. John Wiley & Sons, Inc. 2009

Stipanuk M.H.. Biochemical and physiological aspects of human nutrition. W.B. Saunders Company-An imprint of Elsevier Science, 2000