Fats

– simple glycerol based lipids– compound glycerol based lipids– non-glycerol based lipids

Crude fat(Soxhlet extraction, 8 hours, petroleum ether or hexane; all the fat soluble substances of the food)– simple lipids (triacylglycerols, fats – oils)

Compound glycerol based lipids – Phosphoglycerides

glycerol + fatty acid + phosphoric acid + cholin = lecithin, glycerol + fatty acid + ethanolamine = cephalins

lecithin

–Glycolipids

glycerol + fatty acids + simple sugars (glucose, galactose etc.)The lipids of grasses contain 50-60% glycolipids, mostly galactolipids. 95% of the fatty acids is linolenic acid.

Non-glycerol based lipids•Vaxes

• long chain fatty acid + long chain alcohol• hydrophobic nature, reducing water loss • resistant to breakdown, poorly utilised

•Steroids (biologically active compounds)• cholesterol (present in all animal cells, constituent of cell

membranes, precursor of steroid hormones, and bile acids)• 7-dehydrocholesterol vitamin D3 precursor (animals)• ergosterol vitamin D2 precursor (plants, bacteria, algae)• bile acids • steroid hormones (oestrogens, androgens, progesterone,

cortisol, aldosteron, corticosteron)

•Terpenes• odour and flavour materials,• essential oils• carotenoids, • vitamins A, E and K

steroid hormones

Nutritional role of fats• Energy supplementation of diets• Quality of animal products (fat content, fatty acid

composition)• fat soluble vitamins• Essential fatty acids

– linoleic acid C18:2– α – linolenic acid C18:3– Arachidonic acid C20:4

• flavour compounds• helps in pelleting• carnivores > poultry > pig > ruminants

Common fatty acids of natural fats and oils

Acid Formula Melting point

Fatty acid composition of some common fats and oils

CIS OR TRANS FATTY ACIDS

•These terms refer to the arrangement of hydrogen atoms in unsaturated fatty acids.•Nearly all 'natural' fats contain cis fatty acids. Trans fatty acids, although unsaturated, behave in the body like saturated fatty acids. •They are present in some animal fats and dairy products and are formed during processing in margarine. •The amounts vary, being between 1-7% in butter fat but up to 35% in some margarines.

Omega-3 or n-3 and omega-6 or n-6 fatty acids

•These are terms which describe the position of double bonds within the fatty acid molecule. •These types of fatty acids are advantageous nutritionally. Linoleic acid, an essential fatty acid, which is present in vegetable oils is an n-6 acid. •N-3 fatty acids, present in vegetables and fish oils lower plasma triglycerides and have anti-clotting and anti-inflammatory properties.• α – linolenic acid is a representative of the n-3 group.

DIGESTION OF FATS

•Over 90% of the fat eaten is absorbed from the gut. •Bile is produced by the liver.•The surface of fats is enormously increased by the production of a very fine emulsion in the small intestine. •Fat is broken down by the pancreatic enzyme lipase to glycerol, fatty acids and monoglycerides.•Mixed micelles are formed. •In the cells lining the small intestine, these digestive products are resynthesized into fat, •Fats are incorporated into a shell of water-soluble protein, and enter the bloodstream as chylomicrons. •These particles contain cholesterol as well as being rich in triglycerides.

Digestion and absorption of lipids

The digestibility of fatty acids depends on the length and saturation of fatty acids

• Length of the chain – the digestion of

shorter chain fatty acids is better

• Saturation – absorption rate of

unsaturated fatty acids is higher

steraic acid

oleic acid

linoleic acid

METABOLISM AND TRANSPORT OF FATS

•Lipids are insoluble in water and cannot be carried in solution in the plasma. •The combination of lipids with proteins is called lipo protein. Lipoproteins found in the blood are classified according to their density.

CLASSIFICATION OF LIPOPROTEINS•Very low density lipoprotein (VLDL) - mainly triglyceride•Intermediate density lipoprotein (IDL) - triglyceride/cholesterol•Low density lipoprotein (LDL) - mainly cholesterol•High density lipoprotein (HDL) - phospholipid/cholesterol and the smallest•Chylomicrons-mainly triglyceride, and much the largest particle

After a meal containing fat,•chylomicrons enter the blood. •adipose tissue and skeletal muscle contain an enzyme (lipoprotein lipase) which breaks down the fat in the chylomicrons to fatty acids and glycerol. •these products are then used by the cells for energy or stored as fat.

Between meals, •the liver secretes VLDL which supply the tissues with triglycerides. •The remnants left from VLDL form IDL and then LDL. •LDL is cholesterol-rich, accounting for about 70% of the plasma cholesterol. •It is a risk factor for CHD and has been shown to be the source of cholesterol in atheroma.•If, there is more LDL in the blood than needed by the cells, it enters macrophages (white blood cells) but in an unregulated fashion. •These LDL-packed cells then become 'foam cells' and, deposited within the arterial wall, begin the development of atherosclerosis.

Oxidation of fats • Hydrolysis

– production of free fatty acids– not toxic, but reduced palatability

• Oxidation– it happens at the double bonds– hydropeoxides and ketones are produced – high temperature, ultraviolet light and some metal ions catalyse the

reaction– free radicals react with other fatty acids, cell membranes, sensitive

vitamins (vitamin A, D, E), carotenoids • Antioxidants

– Natural: • tocopherols (vitamin E)• ascorbic acid

– Artificial: BHA (butilated hidroxyanisol) BHT (butilated hidroxytoluen) EMQ (etoxi metilquinone)

Some parameters related to the quality of fats

Nb of peroxides Nb of free fatty acids

Nb of aldehydes

Nb of polymers

time

Nb of polymers

Rel

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s of

pro

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s

Dioxin concentration of several foods (pg/g fat)

fish oil 10,0 mother milk 34,0beef 1,8 cheese 1,4pork 0,43 egg 2,0chicken 1,7 see fish 45,0lamb 1,9 freshwater fish 2,4horse 14,0 eel 28,0goat 4,2 mussel 79,0rabbit 20,0 salmon 16,0milk 1,5 herring 46,0

Europe/USA Japan Eskimo

Arachidonic acid (n-6) 26 21 8,3Eikosapentaenoic acid (n-3) 0,5 1,6 8,0n-6:n-3 fatty acid ratio 50 12 1 cardiovascular mortality 45 1 7

Fatty acid composition of cell membrane phospholipid in different populations (%)

Modification the fatty acid profile of chicken meat

• olive oil oleic acid (Yau et al., 1991)• corn, soybean, sunflower oil linoleic acid (Scaife et al., 1990)• linseed oil linolenic acid (Manilla, 1999)• fish oil EPA, DHA (Ratnayake et al., 1989)

• n-3 long chain fatty acids incorporate mostly into the phospholipid fraction of muscle tissues

• There is a difference among muscles (more into the breast meat compared to tight)

• Feeding diets with increased vitamin E (275 IU/kg) for 3 weeks before slaughter increased the muscle vitamin E content of turkey from 1,6 mg/kg to 5 mg/kg (Sheldon, 1984).

• With broilers 100 IU/kg of vitamin E also increased the vitamin E content to the desirable level (7 mg/kg) (Lin et al., 1980)

Meats containing higher amount of polyunsaturated fatty acids, needs protection

against oxidation

n-3 fatty acid enrichment foods

No. 1. = fishOther meats (pork, poultry)

EggMilk and milk products

Health risks related to fatty acid composition CORONARY HEART DISEASE•Coronary heart disease (CHD) is the narrowing of the lumen of the coronary arteries by atheroma, a deposit which contains cholesterol. The atheroma may then be the site of a blood clot, causing further narrowing and reduction in blood supply. •CHD is a multifactorial disease and a number of risk factors have been identified, prominent among them being raised blood cholesterol. •The level of blood cholesterol is influenced by a number of factors and one of them is the percentage of dietary energy from saturated fats.

CANCERS•Some cancers are associated with a high fat intake. •The mortality from colon cancer in a population is proportional to its saturated fat intake; •The mortality from rectal cancer is proportional to the prevailing P/S ratio.

BREAST CANCER•Breast cancer mortality for a population is roughly proportional to total fat intake.

• People with familial hypercholesterolaemia have few LDL receptors.

• The blood LDL and, therefore, cholesterol level is very high and the risk of premature CHD very great.

• HDL transports excess tissue cholesterol to the liver. • HDL seems to be protective against CHD.

The blood lipids which are commonly measured are:optimal level

total serum cholesterol (fasting) 5.2-5.7 mmol/litre

LDL cholesterol 3.5-4.0 mmol/litretotal triglyceride <2.3 mmol/litre

Dietary fat affects blood lipids and blood clotting in the following ways:

•total plasma cholesterol and LDL are raised by saturated fatty acids, carbon length 12 to 16 (present in dairy products, coconut oil, meat fat) and trans fatty acids (mainly margarine);•cholesterol (highest in offal, egg yolk, mayonnaise and shell-fish) may raise total blood cholesterol but this effect is very variable and less important than that caused by fatty acids;•total plasma cholesterol and LDL are lowered by PUFA of the ω-6 series;•long-chain PUFA of the ω-3 series (fish oils) lower plasma triglycerides, and have anti-clotting and anti-inflammatory properties.

These facts, derived from epidemiological and experimental underlie the recommendations for requirement values.