3.6 - Lipids

lipids

organic compounds

• insoluble in water

• soluble in organic solvents

• variety of different lipids found in plants & animals → all involved in biochemical or physiological functions

• chemically range from fats and oils to complex sterols

• concentrated form of stored energy

  • 1g of fat has 2.25x as much energy as 1g of carbs

lipids+

often found linked to other compounds in order to do their job

• glycolipids

• lipoproteins

• phospholipids

glycolipids

combos of carbs & lipids

• essential for normal cell processes to occur

lipoproteins

combos of lipids & proteins

• important constituents of cells

• carry cholesterol in blood

• 2 types

  • high density

  • low density

high density (HDL) lipoproteins

“good”

• absorb cholesterol & carry it to liver where it gets flushed out of body

low density (LDL) lipoproteins

“bad”

• make up majority of the body cholesterol

phospholipids

contain phosphorus & fatty acids

• are constituents of cellular membranes

sterols

range from compounds such as vitamin D to cholesterol

• important in essential functions of the body

essential fatty acids (EFAs)

nutritionally, lipids provide energy & a source of EFAs in the diet

• composed of fatty acids of varying lengths combined with a glycerol molecule

fatty acids — chains of carbon atoms

• saturated or unsaturated

saturated fatty acids

all bonds on carbon are taken up by hydrogens

unsaturated fatty acids

1 or more double bonds

• monounsaturated: 1 double bond

• polyunsaturated: more than 1 double bond

physical characteristics

fats vs oils → based on consistency at room temp.

• oils = liquid

• fats = solid

oils

composed of short chains of fatty acids or unsaturated fatty acids

fats

contain saturated or longer-chained acids

• fats found in plants & animals are generally in the triglyceride form

  • glycerol backbone with 3 fatty acids attached

digestion & metabolism

MONOGASTRICS

• primary site of fat digestion is the small intestine

  • bile & pancreatic lipase digest dietary fats

• once in the digestive tract, lipids transformed back to triglycerides

• transported to cells to be metabolized

• long-chain fats transported via the lymphatic system

• short-chain fatty acids transported via the circulating blood system

bile

• produced by liver, secreted into duodenum

• primary function: emulsify fat

  • increase surface area of fat molecules, increasing fat exposure to lipase

lipase

• produced by pancreas

• hydrolyzes (breaks down) triglyceride, yielding its component fatty acids & glycerol

  • fatty acids in glycerol are then complexed with bile & absorbed

absorption

• absorption of fatty acids is high → oils absorb more completely than fats

• adequate amounts of fats essential for the absorption of fat-soluble vitamins (A,D,E, & K)

• fats used to synthesize various compounds required by the animal, or stored in fat deposits as an energy release

• end products of energy metabolism are CO_2, H₂O, heat, & ATP

ketosis

when animals metabolize large amounts of fat to provide energy, abnormal conditions cause the energy-metabolizing process to shut down, & ketones are produced

• moderate amounts of ketones produced: can be metabolized by the animals body tissues & used as energy source

• excessive amounts of ketones produced: detrimental to animal → can be detected in urine, milk, & lungs

microbes

• microbes found in ruminants capable of altering dietary fatty acids

• common feedstuffs contain 2-8% fat, most is unsaturated

  • large proportions of unsaturated fats are resaturated by microbes in the rumen

• fat can be “protected”

  • dietary fats that have been treated in manner that protects them from microbe action prevents saturation process from occurring

  • feeding fat in this manner allows for conservation of energy → if fats can get past microbes, directly to small intestine, fat can be absorbed without energy losses

    • microbes utilize energy (to live, breath, etc.) — “charge a fee”

essential fatty acids

required but cannot be synthesized in adequate amounts

• linoleic acid (C18:2)

• linolenic acid (C18:3)

contain 18 carbons & 2/3 double bonds

• omega 6 fatty acids → 1st double bond inserted 6 carbons from the fatty acid terminal end

fish & some aquatic species require fatty acids with the 1st double bond 3 carbons from terminal end → omega 3 fatty acid

essential fatty acid functions/purpose

• integral part of the lipid-protein structure of cell membranes

• important in the structure of prostaglandins

  • hormone-like compounds required for biochemical processes to function

• from feeding perspective: deficients of EFAs do not seem to be a problem in domestic species, EXCEPT poultry

• EFAs distributed widely among most common feedstuffs

  • corn & soybean oils are excellent sources of linolenic & linoleic acids

composition of body fat

fatty acid composition of fat reflects what the animal consumes (especially in monogastrics)

• if animal is fed unsaturated fats → fat deposits become more unsaturated (if amount fed increases, amount in fat deposits increase)

• if oil is fed to poultry or swine, carcass fat becomes less saturated, is softer, has a lower melting point, dramatically changing its processing characteristics

• minor changes in the diet of ruminants do not influence body fat deposits due to the affect of rumen microbes on dietary fats

  • its possible to feed protected fat sources & alter the fatty acid comp. of adipose tissue & milk fat

carcass quality

• if monogastric animal is fed unsaturated fat, fat deposits in body become more unsaturated

  • if pigs are fed diets that are more unsaturated & get more unsaturated pork, can it be advertised as a healthier product?

    • no

      • firm belly with saturated fat → thick, white fat, holds its shape

      • very soft belly that has increased unsaturated fat content → flabby, oily, soft, doesn’t hold its firmness

firm, white, and flaky

typical appearance of animal fat that is saturated

why it matters

lipids contain 2.25x more energy as carbs → lipids are expensive → found in low levels in animal feeds → still must meet fatty acid requirements

• essential fatty acids are distributed widely in the common feedstuffs that are used

lipids summary

• critical in many compounds & functions → often linked to other compounds (ex. glycolipids, lipoproteins)

• classified by structure & physical properties→ saturated vs unsaturated; fats vs oils

• composed of fatty acids organized in triglycerides

• can be stored in adipose tissue → stored & used later

• powerful source of energy, but in low amounts in animal diets → high cost