Lipids: Fats & Oils

Lipids 2006-2007

Lipids Lipids are composed of C, H, O Diverse group fats Fixed oils are esters of long-chain fatty acids and alcohols Diverse group fats Fixed oils Waxes

dehydration synthesis Fat and Fixed oil Structure: glycerol (3C alcohol) + fatty acid fatty acid = long HC “tail” with COOH group at “head” enzyme Note functional group = carboxyl dehydration synthesis

Building Fats Triacylglycerol 3 fatty acids linked to glycerol ester linkage = between OH & COOH

Dehydration synthesis enzyme enzyme enzyme

Structure of Fatty Acids The “tail” of a fatty acid is a long hydrocarbon chain, making it hydrophobic. The “head” of the molecule is a carboxyl group which is hydrophilic. Fatty acids are the main component of soap, where their tails are soluble in oily dirt and their heads are soluble in water to emulsify and wash away the oily dirt. However, when the head end is attached to glycerol to form a fat, that whole molecule is hydrophobic.

Saturated fats All C bonded to H No C=C double bonds long, straight chain most animal fats solid at room temp. contributes to cardiovascular disease (atherosclerosis) = plaque deposits

Unsaturated fats C=C double bonds in the fatty acids plant & fish fats vegetable oils liquid at room temperature The double bonded C prevent the molecules from packing tightly together

Saturated vs. unsaturated 

Chemical constants Acid Values Saponification Value Ester Value Iodine Value Unsaponifiable Matter

ACID VALUE Refers to the number of mg of KOH needed to neutralize the free acids in 1 g of oil. -High acid values occur in oils which are rancid. - Pharmaceutical oil must not have any acidity. Significance Acid value is the measure of hydrolytic rancidity. In general, it gives an indication about edibility of the lipid. Rancid زنخ

SAPONIFICATION VALUE The hydrolysis reaction of lipids (with KOH above) can be used to determine the saponification value of the oil. Saponification value is expressed as the number of mg of KOH needed to neutralize the free acids in, and to hydrolyse the esters in, 1 g of the substance (oil).

ESTER VALUE Ester value: The difference between the saponification and acid values.

IODINE VALUE Iodine value: Gives the measurement of the unsaturation of the oil. The higher the iodine number, the more unsaturated fatty acid bonds are present in a fat. Ex. linseed oil

UNSAPONIFIABLE MATTER The fraction of substances in oil & fat which is not saponified by caustic alkali, but is soluble in ordinary fat solvent is called unsaponifiable matter.

UNSAPONIFIABLE MATTER Unsaponifiable matter consists of compounds such as sterols, which remain after saponification of the triglycerides and the removal of the glycerol and soaps (by using solvents).

SIGNIFICANCE? These constants are important general tests to ensure That the oil is genuine To detect adulteration of fixed oils and fats.

ADULTERATION OF FIXED OILS -Cheap oils are often mixed with more expensive oils as a form of adulteration. -Three of the most commonly used oils are: Sesame oil Cotton seed oil Arachis oil

Examples of valuable fixed oils: Olive oil Cod-liver oil

OLIVE OIL Olive oil is the oil expressed from the ripe fruits of Olea europea (Oleaceae Family).

OLIVE OIL 1st oil expressed: Virgin oil Subsequent extractions: marc is solvent extracted – lower quality oil. Superior grades of oil: Extra-virgin, Virgin, or Refined.

OLIVE OIL: CHARACTERISTICS Olive oil: Pale yellow liquid, sometimes with a green tint. Oil has a slight odour & nice taste.

OLIVE OIL: CONSTANTS If the fruits used to produce the oil have been allowed to ferment, the acid value will be higher than is officially permitted.

OLIVE OIL: CONSTITUENTS Oils from different sources differ slightly in their constituents (composition). This result may be due to the different varieties of olive used, or to climate differences.

Type I Type II BP Limits _______________________ % % % _________________________________________ Oleic Acid 78-86 65-70 56-85 Linoleic Acid 0-7 10-15 3.5-20 Palmitic Acid 9-12 15 7.5-20 Stearic Acid 9-12 15 0.5-5.0

COD-LIVER OIL DEFINITION: Medicinal cod-liver oil is a fixed oil prepared from the fresh liver of the cod, Gadus callarias, & other Gadus spp. (Gadidae Family), under conditions which make it palatable & containing a certain amount of Vitamins.

COLLECTION & EXTRACTION Cod-livers (contain 50% oil), are removed immediately after the fish are caught & transferred to steamers & stored at low temperature.

STORAGE OF COD-LIVER OIL Cod-liver oil should be stored in well-fitted airtight containers. It should be protected from light & stored in a cool, dry place.

Rancid oils are a major source of destructive free radicals in our diet. Exposure to air, heat, and light cause oils to oxidize, become rancid, and form free radicals. Monounsaturated fats, since they have a pair of missing hydrogen atoms are somewhat vulnerable to oxidation. Polyunsaturated oils, which are missing several pairs of hydrogen atoms, are very unstable and highly reactive to oxidation.

COD-LIVER OIL: CONSTITUENTS The oil consists of glycerides of unsaturated (85%) and saturated (15%) acids. Saturated fatty acids: myristic acid, palmitic acid & traces of stearic acid.

ACTIONS & USES The medicinal properties of cod-liver oil are mainly due to the Vitamins A & D. It is widely used in underdeveloped countries for the prevention & treatment of rickets. Europe & USA: Traditionally used as a vitamin supplement. Recent research: relief of rheumatic pains & joint & muscle stiffness. Reduces blood cholesterol. Protects against CVD