School Science Lessons
2024-04-17
Fats in food
Contents
3.9.1 Cholesterol
3.9.2 Classification of fats
3.9.3 Composition of edible oils
3.9.4 Fats in animals and plants
3.9.5 Fatty acids
3.9.6 Fatty acids, ω-3 and ω-6 fatty acids
3.9.7 Heating fats
3.9.8 Hydrogenation, cis-trans fatty acids
3.9.9 Rancidity of fats
3.9.10 Trans fats, Omega-fatty acids
3.9.1 Cholesterol
1. Cholesterol, C27H46O, modified steroid, lipid molecule, about 25% biological cell membranes, controls membrane permeability.
It is synthesized in the small intestine and liver
High cholesterol levels in the blood indicate the potential for atherosclerosis and coronary heart disease.
Cholesterol is a fat-like molecule, an alcohol, base of all steroids, e.g. sex hormones, bile acids, vitamin D and cortisone.
Cholesterol is not a fat, but a steroidal alcohol.
It has 27 carbon atoms, so it is not a terpene.
It is essential for the blood and cell membranes and is found in all the cells of the body.
It is produced in the liver and also comes from foods of animal origin.
It is the main sterol of animals, in body tissues, the brain and spinal cord, and in animal fats and oils.
It occurs naturally in Acanthus ilicifolius and Amaranthus hybridus.
Cholesterol is an animal tissue sterol, emulsifying, in date palm Phoenix, in marine red algae Rhodophyceae.
2. Cholesterol in the blood becomes coated with a phospholipid protein envelope called lipoprotein in a high density form (HDL) and a low density form (LDL).
In countries where people eat large amounts of meat and dairy products, their diets are high in cholesterol and saturated fats and so the mortality rate from heart disease is high.
In countries where diets are low in cholesterol and rich in the polyunsaturated fats found in vegetable oils and fish, the death rate from coronary disease is lower.
Vegetable oils contain phytosterols instead of cholesterol.
Isolation of ergosterol used to be used as evidence proving the addition of vegetable oil to animal products.
Atherosclerosis occurs when excess LDL cholesterol circulates in the blood, accumulates in the inner walls of the arteries to the heart and brain, and reacts with other substances to form a plaque that can
clog
those arteries.
A blood clot can form to block a narrowed artery and can cause a heart attack or stroke.
So the levels of HDL cholesterol and LDL cholesterol in the blood are measured to evaluate the risk of heart attack.
An LDL cholesterol level < 130 mg / dL is optimal for most people.
However, an LDL cholesterol level > 130 mg / dL reflects an increased risk of heart disease, so LDL cholesterol is called "bad" cholesterol.
Up to one fourth of blood cholesterol is carried by high density lipoprotein (HDL).
It is called "good" cholesterol, because it may protect against heart attack by carrying cholesterol away from the arteries and back to the liver, to be excreted from the body.
Most people can raise their HDL (good cholesterol) levels by exercising, not smoking and staying at a healthy weight.
3. Triglyceride levels < 150 mg / dL are normal.
Triglyceride levels from 150-199 are borderline high.
Levels that are borderline high or high (200 mg / dL to 499 mg / dL) may need medical treatment.
Triglyceride levels of 500 mg / dL or above are very high.
Doctors need to treat high triglycerides in people who also have high LDL cholesterol levels.
People with high triglycerides often have a high total cholesterol, a high LDL cholesterol and a low HDL cholesterol level.
People with heart disease, diabetes or who are obese are likely to have high triglycerides level, high LDL cholesterol level and a low HDL cholesterol level.
4. LPG cholesterol is a genetic variation of plasma LDL that may cause fatty deposits in arteries.
Lpa is a genetic variation of plasma LDL.
A high level of Lpa is an important risk factor for developing fatty deposits in arteries prematurely.
The way an increased Lpa contributes to disease is not understood.
The lesions in artery walls contain substances that may interact with Lpa leading to the build up of fatty deposits.
5. Cholesterol, saturated fats and heart disease, alternative views
Some people do not believe in any connection between cholesterol and heart disease:
"It's amazing how long the myths concerning the connection between saturated fats and heart disease and cholesterol can survive despite evidence to the contrary when considering the statistics and despite the serious side effects of the drugs.
Even Ancel Keys, (the initial experimenter), has said that there is no connection between cholesterol and heart disease.
Coconuts and butter and pasture fed beef are good for you! Just read Uffe Ravnskov's "The Cholesterol Myths."
I cannot think of any topic of debate that has more lies, half-truths, serious omissions, bad science and general intellectual dishonesty than saturated fat and cholesterol.
This I believe is down to vested interests.
Both the production of margarine and statins are highly profitable.
The only scientific study showing saturated fat in negative light was the Seven Countries done by Ancell Keys, where he in fact had data from 22 countries, but cherry picked data to show a pre-determined outcome.
This is classic bad science.
No other scientific study concurs with his finding since from the 1930's in the USA as the pre-capita consumption of traditional animal fats decreased and the consumption
of vegetable oil and margarine went up, heart disease took off and increased rapidly, so if anything, saturated fat protects against heart disease.
As it has been pointed out on the radio program, the consumption of coconuts and coconut oil is high in the Philippines and Pacific Islands.
This being the case if saturated fat causes heart, disease then heart disease should be highly prevalent in these places, but this does not appear to be the case.
What does cause heart disease is trans fat found in margarine and hardened vegetable oil.
It is a by product of partial hydrogenation.
3.9.2 Classification of fats
1. Saponification value from hydrolysis of a fats into component fatty acids, as their anions or soaps, and glycerol.
Saponification value = number of milligrams of potassium hydroxide to saponify one gram of fat (or oil).
It is a measure of the average chain length, molecular mass of the fatty acids.
2. Fat and saponification value:
Coconut oil 250-260, Butter 245-255, Lard (pig fat) 193-200, Peanut oil 185-195, Linseed oil, 189-196. 3.
Iodine value measures the number of double bonds in the fat.
Iodine reacts with the double bond.
Iodine value is the number of grams of iodine that react with 100 g of fat or oil.
Fats with low iodine values are saturated.
Fats with high iodine values are polyunsaturated.
Fat and iodine value: Coconut oil 8-10, Butter 26-45, Lard 46-66, Peanut oil 83-98, Linseed oil 170-204. 3.
3. Acid value measures how much glycerides in the fat or oil have been decomposed to free acid.
This is regulated by food standards codes.
4. Peroxide value measures the oxygen taken up by the oil to form peroxides and is a measure of the freshness of the oil.
This regulated by food standards codes.
5. Oxygen uptake.
If polyunsaturated fats are incubated at 60oC, they gain weight from oxygen uptake.
3.9.3 Composition of edible oils
Table 1.1.1
3.9.4 Fats in animals and plants
1. Fats and oils, animal fat (tallow, suet, dripping is fat from beef cattle), (lard is pig fat), soap is made from animal fat and hydroxide
Suet fat
Suet is solid fat around kidneys of cattle and sheep, to be melted to form tallow.
Suet pudding is made of suet + flour, wrapped in a cloth, then boiled.
Tallow fat
Tallow is hard fat formed from rendering suet.
It contains stearin, palmitin, olein, and is used for candles and soap.
2. Fats and oils are used to store, transport and utilize the fatty acids that an organism requires for its metabolic processes.
Energy storage in animals: fat 38 kj / g, carbohydrates 17 kj / g, protein 23 kj / g.
Fats store water and when metabolized in the body to produce energy, they also produce water, e.g. fatty hump of the camel.
Plants, fungi, yeasts and bacteria, can synthesize both fats and their component fatty acids.
Animals can synthesize most of their fatty acid needs, but they prefer to ingest plant foods and modify them to their own needs.
Only plants can synthesize linoleic and linolenic acids, but animals can increase the chain length and further increase unsaturation, e.g. fish oils, that are rich in unsaturated acids.
Saturated fatty acids are predominantly present in fats that are solid at room temperature, e.g. milk, butter and animal fats.
Saturated fats may raise the level of "bad" cholesterol leading to hardening of the arteries, high blood pressure, heart disease and strokes.
Animals produce mainly saturated fats, because their fats also have a structural support function and must not be too fluid.
Some animals can maintain a high temperature through internal heating, insulation and behaviour.
Unsaturated fatty acids may be mono-unsaturated or polyunsaturated.
Mono-unsaturated fatty acids, e.g. oleic acid, are found in most animal and plant fats and oils, especially olive oil.
Unsaturated fatty acids occur mainly in oils.
Most fats and oils contain a mixture of saturated and unsaturated fatty acids, but in widely varying proportions.
An intake of fat in the diet is essential as some fatty acids are required for important functions in the body.
Fat soluble vitamins A, D, E and K must also be provided by food containing fat.
A fat free diet is not only difficult to prepare, but is also very unpalatable.
3. The so-called "bad cholesterol" is the LDL (low density lipoprotein) cholesterol used to build body cells
Excess cholesterol can form plaque on the walls of arteries to the heart and brain, causing atherosclerosis.
The "good cholesterol" is HDL (high density lipoprotein) cholesterol produced in the liver and intestines that removes excess cholesterol from atherosclerosis plaques.
It may protect from heart attack.
Electrophoresis is used to separate the LDL fraction of total cholesterol to measure the HDL and LDL levels and determine the risk factors for coronary heart disease.
4. Polyunsaturated fatty acids, e.g. linoleic acid, linolenic acid, are found mainly in vegetable oils.
Polyunsaturated fats are essential to animals as building blocks and for controlling the cholesterol content of the blood.
Plants produce mainly unsaturated oils that allow them to withstand extremes of temperature, because their fats or oils are fluid at low temperatures.
Polyunsaturated fats lower "bad" cholesterol, but also lower "good" cholesterol.
Polyunsaturated fats are found in margarine, vegetable oils and seed oils.
Some research claims that polyunsaturated fats may be are oxidized into "free radicals" that contribute to the development of some cancers and accelerate ageing.
5. Mono-unsaturated fats are the "good" fats and should make up most of the fats in a diet, up to about 30% of a diet.
Saturated fat in the diet can raise the level of blood cholesterol to increase the risk of heart disease from atherosclerosis, fatty plaques on the walls of blood vessels.
Unsaturated fat can form free radicals by lipid peroxidation, leading to cancer and accelerated ageing.
So both saturated and unsaturated fat can have health hazards!
3.9.5 Fatty acids
1. The group of saturated and unsaturated aliphatic carboxylic acids are called fatty acids and are found as esters in fats and oils.
Lower carbon fatty acids are corrosive liquids with strong odour and are soluble in water.
Higher carbon fatty acids are oily liquids with unpleasant smell and are only slightly soluble in water.
Fatty acids from C10 onwards are usually solids and are insoluble in water.
Fatty acid are aliphatic acids with chain lengths 6 to 30, and occur in all fats.
Saturated fatty acids, e.g. propionic acid, CH3CH2CO2H, and monounsaturated fatty acids, e.g. oleic acid, C18H34O2, are synthesized by the body.
Polyunsaturated fatty acids, e.g. linolenic acid, C18H30O2, must be in the diet.
Oleic acid has one double bond: CH3−(CH2)7−CH=CH−(CH2)7−COOH
2. Fats, oils and some waxes are the naturally occurring esters of long, straight chain carboxylic acids.
These esters are the materials from which soaps are made.
At room temperature, fats are solid or semi-solid and oils are liquids.
alcohol + organic acid --> ester + water glycerol + fatty acid --> fats or oils + water
All fats form from glycerol, glycerine, propan-1,2,3-triol, CH2OHCHOHCH2OH.
3. The fatty acid part of the fat differs as follows:
* in the length of the chain, which controls the molecular mass, and
* in the number and position of the double bonds, unsaturation.
4. The three main groups of fatty acids are as follows:
* Saturated fatty acids, e.g. stearic acid,
* Straight chain unsaturated fatty acids, e.g. oleic acid,
* Polyunsaturated fatty acids, e.g. linoleic acid.
5. The normal saturated fatty acids have the general formula, CH3(CH2)nCOOH,
where n is usually an even number from 2 to 24, e.g. stearic acid (n=16) lauric acid (n=10).
Milk contains short chain fatty acids, n < 10.
6. The building block for fatty acids is the acetate ion, CH3COO-.
The most important unsaturated fatty acids have 18 carbon atoms with one double bond in the middle of the chain, called mono-unsaturated fatty acids.
Polyunsaturated fatty acids have more double bonds between the middle double bond and the carboxyl group, COOH.
Atoms can rotate about single bonds, but not about double bonds, so two arrangements are possible called "cis" and "trans".
Most double bonds in natural fats and oils are cis, e.g. oleic acid in olive oil.
Fatty acids with the cis double bond do not pack together easily, so have a low melting point of double bond containing material, i.e. oils.
Substances made up of shorter chains also melt at lower temperatures.
Chemists describe polyunsaturated fatty acids as having more than one cis-methylene interrupted double bond.
7. The poly unsaturated fatty acids linoleic acid, linolenic acid and arachidonic acids are essential fatty acids in the diet to prevent, atheroma,
("hardening of the arteries"), and synthesize prostaglandins.
Saturated fatty acids with no double bonds are linked to the development of atheroma.
Fatty acids in plants occur as esters of glycerol or other hydroxy compound, or amides of long chain amines, e.g sphingenine.
Fatty acids have trivial and systemic names and the molecule may be saturated (no double bonds), or unsaturated (one or more double bonds).
The products called "natural oils" are not necessarily unsaturated fats.
8. Fatty acids are open chain aliphatic monocarboxylic acids derived from, or in esterified form in an animal or vegetable fat, oil or wax.
Natural fatty acids usually have an unbranched chain of 4 to 28 carbons that may be saturated or unsaturated.
All acyclic aliphatic carboxylic acids may be called fatty acids.
Carboxylic acids (fatty acids), R-(COOH)n, contain the carboxyl group -CO.OH, i.e -COOH, carbonyl group attached to an hydroxyl group, are weak acids, e.g ethanoic acid (acetic acid) CH3COOH, so the general formula is RCOOH.
An anion formed from carboxylic acid is called a carboxylate.
The carbonyl group (carboxy) is -COOH.
Oxo acids have a carboxy group and an aldehyde or ketone group in the same molecule, e.g. HC(=O)CH2CH2CH2C(=O)OH, 5-oxopentanoic acid.
Carboxylic acids, one carboxyl group (R-COOH, RC(=O)OH) (-oic acid) fatty acids, e.g. methanoic acid (formic acid) (HCOOH) ethanoic acid (acetic acid) (CH3COOH, CH3C=OOH).
Fatty acids list:
Arachidic acid, C20H40O2, in seed oils, in peanut (Arachis hypogaea)
Arachidonic acid, C20H32O2
Behenic acid Behenic acid, Docosanoic acid. C22H44O2
Chaulmoorgric acid, C18H32O2, in Chaulmoogra (Hydnocarpus wightiana)
Decanoic acid, Capric acid, C10H20O2, in chilli (Capsicum species)
Erucic acid, C22H42O2, in nasturtium (Tropaeolum majus)
Hexanoic acid, Caproic acid, C6H12O2, CH3(CH2)4COOH
Octanoic acid, Caprylic acid, C8H16O2
Hexanoic acid, Caproic acid
Lauric acid, Dodecanoic acid, C12H24O2, in coconut (Cocos nucifera)
Linoleic acid, C18H32O2, in borage (Borago officinalis)
Linolenic acid, C18H30O2, in perilla (Perilla frutescens var. crispa).
Myristic acid,Tetradecanoic acid, C14H28O2, in orris (Iris florentina)
Oleic acid, C18H34O2, C8H17CH=CH(CH2)7COOH, in Chinese date (Zizyphus jujuba)
Palmitic acid, Hexadecanoic acid, C16H32O2, in abelmosk (Abelmoschus moschatus)
Palmitoleic acid, C16H30O2, in coconut (Cocos nucifera)
Petroselenic acid, C20H40O2, in parsley (Petroselinum crispum)
Ricinoleic acid, C20H40O2, in golden shower tree (Cassia fistula)
Stearic acid, C18H36O2, CH3(CH2)16COOH, in coconut (Cocos nucifera)
Vaccenic acid, C18H34O2, in milkweed (Asclepias syriaca)
3.9.6 Fatty acids, ω-3 and ω-6 fatty acids
The ω-3 fatty acids is a family of polyunsaturated fatty acids.
The parent ω-3-α-linolenic acid (ALA) is obtained from the diet and is polyunsaturated with 8 carbon atoms and 3 double bonds.
The long chain ω-3 fatty acids eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA, can be synthesized from dietary ALA, but in seems that EPA and DHA should be obtained from the diet containing oily fish and fish oil, as well as fortified bread and fruit juice.
ALA, EPA and DHA are important role for structural membrane lipids, in nerve tissue and the retina beside a wide range of functions in cells and tissues.
3.9.7 Heating fats
Heating fats
1. Smoke point is the temperature at which a fat breaks down into visible gaseous products and thin wisps of bluish smoke begin to rise from the surface.
Smoke point, smoking point, falls with the continued use for cooking, because the oil or fat decomposes and the free fatty acids have a lower smoke point.
So the higher the initial smoke point, the longer the fat is usable before it starts to smoke.
Smoke point of an oil or fat is an important piece of information for consumers and should be listed on food labels.
2. Flash point is the higher temperature when fat bursts of flame start.
3. Ignition temperature, is the higher temperature at which the entire surface of the frying medium becomes covered with flame.
4. P/S ratio is the ratio of polyunsaturated fatty acids to the saturated fatty acids present.
In western diets the ratio is about 0.6 and increasing it to 1.0 may reduce the risk of atherosclerosis and coronary heart disease.
Heating may not change the P/S ratio of polyunsaturated oils, but it causes formation of oxidized compounds, which tend to destroy vitamin E content and make oils unpalatable.
Changes in the peroxide value of oils after heating reveal how heating oxidizes oils.
5. Smoke point and P/S ratio, approximate values
* Safflower oil: smoke point: 246oC, P/S ratio: 6.0
* Sunflower oil: smoke point: 229oC, P/S ratio: 4.7
* Maize oil: smoke point: 229oC, P/S ratio: 3.1
* Peanut oil: smoke point: 246oC, P/S ratio: 1.9
* Soybean oil: smoke point: 256oC, P/S ratio: 3.7
* Olive oil: smoke point: 204oC, P/S ratio: 0.5
3.9.8 Hydrogenation, cis-trans fatty acids
3[CH2O(CO)(CH2)7CH==CH(CH2)7CH3] + 3H2 --> 3[CH2O(CO)(CH2)16CH]
glyceryl trioleate + hydrogen (nickel catalyst) + heat --> glyceryl tristearate
Hydrogenation means to add hydrogen to a molecule.
Unsaturated fats can be saturated by adding hydrogen to the double bonds with a nickel catalyst.
Hydrogenation converts a substance with the properties of a liquid vegetable oil into a substance with the properties of a solid animal fat.
For example, linoleic and oleic acids turn into stearic acid.
The manufacturing process may cause some hydrogenation of unsaturated fatty acids.
Processed oils such as shortenings may contain a high proportion of fats changed by hydrogenation.
In nature, most unsaturated fatty acids are cis fatty acids, i.e. the hydrogen atoms are on the same side of the double carbon bond.
In trans fatty acids the two hydrogen atoms are on opposite sides of the double bond.
Trans double bonds can occur in nature as the result of fermentation in grazing animals, so people eat them in the form of meat and dairy products.
Trans double bonds are also formed during the hydrogenation of vegetable or fish oils.
French fries (fried potato chips) donuts, and other snack foods are high in trans fatty acids.
Manufacturers may hydrogenate polyunsaturated oils to help foods stay fresh or to obtain a solid fat product, e.g. margarine.
Trans fatty acids, i.e. hydrogenated fats, tend to raise total blood cholesterol levels, and raise LDL bad cholesterol and lower HDL good cholesterol.
In some countries, governments have required fast food companies to commit to reducing trans fats in their cooking and listing trans fat content on labels.
Some fast food companies have claimed that consumers do not like the taste of products if all trans fats are eliminated.
However, apparently, if only a small proportion of trans fats are used, taste is not a problem.
In other countries, trans fats in cooking have been banned altogether by legislation.
3.9.9 Rancidity of fats
Oxygen in the air oxidizes unsaturated fats adjacent to the double bond to produce smaller easily evaporated volatile compounds with a rancid smell.
Most of the fatty acids in butter are C16 -C18, but shorter chain fatty acids are also present.
The acid from rancid butter is 1,3-butadiene: CH2=CH-CH=CH2, a butane with two double bonds, bivinyl butyric acid: C3H7COOH.
Cheeses made from milk with more short chain fatty acids have a stronger smell.
Margarine rarely becomes rancid, because the longer chain fatty acids must first be broken before the short chain, rancid smelling compounds form.
Purchased fats and oils have added antioxidants to prevent rancid compounds from forming.
The same short chain acids in rancid butter are present in human perspiration.
3.9.10 Trans fats, Omega-fatty acids
1. Trans fats are trans isomer (E-isomer) fatty acids.
Fatty acids, together with glycerine, are the building blocks of all fats and oils.
Trans fatty acids are unsaturated but, unlike the "good" unsaturated fatty acids found in fish and vegetable oils, behave similarly to saturated fats in the body and have similar health issues.
Trans fats can be found naturally in meat and milk from certain animals and as a product of fats and oils altered by industrial processes, such as hydrogenation.
2. Hydrogenation is widely used to solidify liquid vegetable oils to make products such as margarine and shortenings and involves adding hydrogen to the oils.
Trans fats are not formed through deep frying food in vegetable oils.
However, manufactured fats such as margarine spreads, fats used in deep frying and fats used in pastry dough, are likely to contain some trans fats, because they improve the firmness of the product and the products are less likely to be damaged by oxidation, or heat.
Trans fats make cooking oils more stable.
3. Some fats are good for us and can help reduce the "bad" type of cholesterol that causes a lot of health problems.
These good fats include polyunsaturated, monounsaturated fats, omega-3 fatty acids, omega-6 fatty acids or omega-9 fatty acids.
Both trans fats and saturated fats increases the level of "bad" cholesterol, with trans fats also decreasing the level of "good" cholesterol.
This can cause a number of serious health problems.
4. Studies have shown that Australians consume relatively low amounts of trans fatty acids compared with people in other countries.
However, the amount of saturated fats consumed by Australians is of greater concern so the amount of total fat and the amount of saturated fat must be declared on all food labels.
The amount of trans fat in food must be declared on the label if a nutrition claim is made about cholesterol, polyunsaturated, monounsaturated fats, omega-3 fatty acids, omega-6 fatty acids or omega-9 fatty acids.
5. Omega-fatty acids
16.3.8.4 Unsaturated fatty acids
Omega-3 fatty acids cannot be manufactured in the body.
The omega-3 fatty acids group have the first double bond between the third and fourth carbon atoms counting from the right, i.e. from the methyl group.
Omega-3 fatty acids, C60H92O6, N-3 polyunsaturated fatty acid, first unsaturated bond in the third position from the omega carbon, (the carbon atom of the methyl group at the end of the hydrocarbon chain), e.g. Linolenic acid, α-linolenic acid, C18H30O2,
CH3(CH2)CH=CH(CH2)CH=CH(CH2)CH=CH(CH2)7COOH.
Omega-3 fatty acids may reduce serum triglycerides, prevent insulin resistance, improve lipid profile, prolong bleeding times, reduce platelet counts, and decrease platelet adhesiveness, e.g. Alpha-linoleic acid, C18H30O2, in seed oils, (rapeseed), and e.g. Eicosapenaenoic acid, C20H30O2, in cod liver oil.
Omega-6 fatty acids,C38H64O4, N-3 polyunsaturated fatty acid, first unsaturated bond in the sixth position from the omega carbon, e.g. Linolenic acid, C18H32O2, in grapeseed oil.
Omega-9 fatty acids, avocado oil is 70% omega-9 fatty acid, e.g. Oleic acid, C18H34O2 in olive oil and macadamia oil, e.g.Erucic acid Erucic acid
6. Fish oil is a dietary source of omega-3 fatty acids to improve muscle activity and cell growth.
Fish oil contains two omega-3 fatty acids, docosahexaenoic acid, (DHA), C22H32O2, and eicosapentaenoic, (EPA), C20H30O2.
A diet rich in eicosapentaenoic acid lowers serum lipid concentration, reduces incidence of cardiovascular disorders, prevents platelet aggregation.
Fish oils can be in the diet by consuming salmon, mackerel, mussels, and oysters.