Lipids: Waxes and Triacylglycerols

Vocabulary and chemical properties of waxes and triacylglycerols (fats and oils), including reactions such as hydrogenation, hydrolysis, and saponification.

Waxes

Esters of saturated fatty acids and long-chain alcohols, each containing from $14$ to $30$ carbon atoms, that serve as coatings to prevent water loss by leaves of plants.

Beeswax

A wax with the formula $CH_3(CH_2)<em>{14} ext{-C-O-}(CH_2)</em>{29} ext{-}CH_3$ sourced from honeycombs and used in candles, shoe polish, and wax paper.

Carnauba wax

A wax with the formula $CH_3(CH_2)<em>{24} ext{-C-O-}(CH_2)</em>{29} ext{-}CH_3$ sourced from the Brazilian palm tree used for furniture, cars, floors, shoes, and cosmetics.

Jojoba wax

A wax with the formula $CH_3(CH_2)<em>{18} ext{-C-O-}(CH_2)</em>{19} ext{-}CH_3$ sourced from the Jojoba bush used in candles, soaps, and cosmetics.

Triacylglycerols (triglycerides)

The major form of energy storage for animals, consisting of esters of glycerol (a trihydroxy alcohol) and three fatty acids.

Glyceryl tristearate

Also known by the common name tristearin, this triacylglycerol is formed when three stearic acids react with glycerol.

Mixed Triacylglycerols

Triacylglycerols that contain different fatty acids, such as a combination of stearic, oleic, and palmitic acids.

Fat

A substance that is usually solid at room temperature and typically comes from animal sources such as meat, whole milk, butter, and cheese.

Oil

A substance that is usually liquid at room temperature and is typically obtained from plant sources such as olive, peanut, corn, cottonseed, safflower seed, and sunflower seed.

Hydrogenation

A reaction where hydrogen gas is bubbled through heated oil in the presence of a nickel ($Ni$) catalyst to convert double bonds in unsaturated fatty acids into carbon–carbon single bonds.

Trans fatty acids

Fatty acids with bulky groups on opposite sides of the $C=C$ bond that can form during partial hydrogenation; they raise LDL-cholesterol and lower HDL-cholesterol.

Hydrolysis

The process where triacylglycerols split into glycerol and three fatty acids, requiring a strong acid such as $HCl$ or $H_2SO_4$, or digestive enzymes called lipases.

Saponification

The reaction of a fat with a strong base ($NaOH$ or $KOH$) in the presence of heat to produce glycerol and the salts of fatty acids (soap).

Esterification (Lipid Reaction)

The reaction where three fatty acids and glycerol combine to produce triacylglycerol and three water ($H_2O$) molecules.