Food Chem Exam 2: Lipids

What are lipids?

Fats and oils, soluble in organic, non-polar solvents

True or false? Fats are solid at room temp.

True

True or false? Oils are solid at room temp.

False

What is the simplest lipid and what is its general formula?

Fatty acids, R-COOH

How do fatty acids differ?

Length of hydrocarbon tail, degree of unsaturation, double bond position, essentiality

Are most fatty acids CIS or TRANS (in relation to isomerism)?

Cis (lower melting point)

What is a glycerol?

Three fatty acids linked together

What two types of molecules link to form an ester?

Glycerols and fatty acids

What kind of functional group does a glycerol & fatty acid form?

Ester

How does melting point change with fatty acids?

Lowers with less Carbons

Lowers with increased degree of saturation

What is the least stable polymorphic form of crystals in fat?

Alpha crystals

What is the desired type of fat crystal in chocolate?

Beta crystal

What is the desired type of fat crystal in margarine

Beta prime crystal

What are the three ingredients for hydrogenation?

Nickel, hydrogen, and pressure

What is interesterificatin?

Fatty acid rearrangement

What is lipid oxidation?

Series of chemical rxns initiated when Oxygen interacts w/ unsaturated lipids

What are the primary reaction products of lipid oxidation?

Peroxides and conjugated dienes

What are the secondary reaction products of lipid oxidation?

aldehydes, ketones, alcohols, hydrocarbons

What is an alternative way to create solid fats from oils apart from hydrogenation?

Interesterification

What is needed for lipid oxidation to take place?

Unsaturated fatty acids and oxygen

Which radical is created at both the initiation and propagation steps of lipid oxidation reaction?

Alkyl radical

What factors increase oxidation rate?

lipid type, oxygen, pro-oxidants, light, heat

What factors decrease oxidation rate?

Antioxidants, chelating agents

What is an antioxidant?

Free radical scavengers, lower energy of free radicals so that they are less reactive

Can polyphenols also work as antioxidants? True or false?

True

What does alpha-tocopherol do as an antioxidant?

Gives Hydrogen away to free radical without becoming a free radical itself (because of aromatic ring)

What is hydrolytic rancidity?

Uptake of a water molecule that is usually promoted by action of lipase, or by alkaline heat

What happens to triglyceride molecule during lipolysis?

Yields three fatty acids and one triglyceride

What is the most common phospholipid?

Lecithin

What is an amphiphilic molecule?

A molecule that has polar & non-polar regions

What does HLB mean?

Hydrophilic-Lipophilic Balance

Most emulsifiers are not hydrophilic, true or false?

False

What is the formula for HLB?

7 + sum (hydrophilic groups) - sum (hydrophobic groups)