Lipids Flashcards
name a simple and a compound lipid
fatty acid, steroids, carotenoids and compound is acylglycerols, phospholipids and waxes. the two first are glycerol plus fatty acids
what is mandatory to declare on foods
fat- and part saturated fat, protein, carbohydrates, salt
which bond is it between glycerol and the fatty acids
ester bond
which enzyme catalyze synthesis and degradation of trigycerides
synthesis by acyltransferase and degradation by lipase
what are the 2 shortenings of omega 3
EPA and DHA
what does the n and x stand for in n:x
n=number of carbons and x=number of double bonds
T/F the shorter the chain the higher melting point
true
what is the soxhlet method
it extract oil and fat from solid materials by repeated washing with an organic solvent, usually hexane or petroleum ether. but it is not good to extract membrane lipids like those in algae
what is B&D
using chloroform:methanlon:water in the ratio 1:2:0 8 to isolate and purify lipids
what is the Saponification value
the fatty chain length
what’s the acid value a measure of
how much free fatty acids
iodine value?
a measure of the no of double bonds
what major compounds does the phospholipid consists of
Choline, phosphate, glycerol and fatty acids
what is Lecithin
a common phospolipid in egg yolk
for what are phospholipids good for
cell membrane and emulisifyers
T/F when fats and oils are processed phospholipids and free fatty acids are removed
true
how do you bleach an oil
with activated carbon
what is hydrogenation of lipids
the conversion of liquid oil to semisolid or plastic fats. it improves oxidative stability. the principle is: mixing oil with catalyst (Ni), heat to 140-220 then agitation of H2 under high pressure
what is the selectivity ratio (SR)
k2/k3 which is the ratio k2=linoleic acid to oleic and k3=oleic to stearic. high SR values are preferred
how to make good hydrogenation
have enough H and run to completion
what are critical conditions during hydrogenation
high temperature (reaction faster than H diffusion) and high catalytic conc. (difficult to saturate catalyst with h)
what is inter-esterification
a random redistribution of fatty acids on the glycerol molecule - softer melting characteristics
what is the effect of Benecol
blood cholesterol lowering effect. it’s a fatty acid ester of a plant sterol
what is the difference between lipolytic and oxidative rancidity
the first is the fatty acid lipolysis (level of free fatty acids) and the last is the reaction between oxygen and fatty acids
what are the food quality changes of lipid oxidation
rancid smell and taste, color and texture changes and reduced nutritional value
what is created in the first and second step in lipid oxidation
- alkyl radical (a free radical took H from lipid, LH to L) and 2. peroxy radical (O2 inserted, LOO)
what’s the primary, secondary and tertiary products of lipid oxidation
- hydroperoxide (LOOH) H from another LH and 2. aldehydes and ketones.. that are volatiles and taste and 3. interaction products that give color and texture changes(in protein products only)
what are the 3 possible initiation steps for lipid oxidation
- singlet oxygen (by light) O2 + LH to Peroxy radical 2. initiator (OH, LO, LOO, activated heme, Fe) i.e a compound that can remove a H from a fatty acid to fatty acid radical L 3. enzyme catalyzed (lipoxygenase) to form peroxy radical
what is the name of the biological production of hydroxyl radicals
Fenton reaction
which fatty acids are most prone of lipid oxidation
unsaturated
what is chain branching
the cleavage of hydroperoxide to secondary oxidation products. often volatile. catalyzed by iron/heme or other heavy metal
what happens in the termination step of lipid oxidation
two radicals react with each other under formation of a stable product
are lipid oxidation dangerous
probably not. not in the amount we eat, our senses would not let us eat super rancid
name some good things about lipid oxidation
bleaching of flour, improved dough forming properties, formation of CLA in milk fat
name some pro-oxidants
metals Fe and Cu, radicals, oxygenase enzymes and reducing systems
name some preventive inhibitors of lipid oxidation
they either inactivate O2 (catalase, peroxidase, ascorbate, betakaroten)or metals(nucleotides, amino acids, peptides and organic acids).
name some antioxidants
GSH-px and vitamins such as ascorbate, ubiquinol and Tocoferol. BAH, BHT
how does lipid oxidation relate to aw
high at low aw then goes down at the lowest at aw 0.4 then goes up
name some factors that prevent lipid oxidation
light, temp., mincing/oxygen, moisture and pH (lower pH faster oxidation), lipid hydrogenation
what are the typical structure of an antioxidant
ring structure
which are the 2 most common lipid oxidation measures
peroxide value: measures the conc. of peroxide. the hydroperoxides oxidize Fe2+ to Fe3+ that further reacts with ammonium cyanate and forms red complex. TBA-test: TBA reacts with products formed when hydroperoxides decompose. that forms a pink complex
what are the 3 polymorphic behaviours of fats?
alpha, beta prim and beta
what is the structure of the three fat crystal structures
alpha can rotate freely and are unstable. beta’ is perpendicular and not as movable. beta is most stable and closely packed
How does the bilayer look in melted form
the methyl terrace and chair structure
what is the fat structure difference between alpha, beta’ and beta?
two fatty acids on top of each other in 1 and in beta there are three which make it more densely packed. more even fatty acid lengths give a more even methyl terrace
what are the 3 most common fatty acids in cocoa butter
stearic acid, palmitic acid and oleic acid.
what is the tempering of cocoa butter
you lower the temperature 2 times and the beta form develops just below 33 °C
name three alternatives to cocoa butter
CBE - fats with similar fatty acid composition (palm oil, sheanut) CBR - hydrogenated soya oil/rapeseed oil (the easiest) CBS- fractionated palm kernel oil
what is food dispersions
a system of discrete particles in a continuous phase
what is a colloid
a dispersion with particle size between 10 nm and 0.1 mm
what are surfactants
surface active agents which are either small amphiphilic molecules or polymers
what is the action of an emulsifier
lowers the interfacial tension up to critical micelle formation where emulsifier causes micelles. it stabilizes the emulsion
what is Bancroft’s rule
when making a emulsion of oil, water and emulsifier, the continuous phase will become the one in which the emulsifier is best soluble
what is the Gibbs-Marangoni effect
when two droplets approach each other the contious phase is forced out and the surfactant is dragged along the droplets surface. this results in a surfactant gradient that will force droplets apart.
what is the DLVO theory
The resulting force w is a measure on the stability of the colloid. there is a van der Waals attraction force within droplets and electrostatic repulsion force between them.
describe coalescence
it’s the process by which emulsified particles merge together to form a larger particle. starch can prevent this by making liquid more viscous
polymeric vs. electrostatic stabilization
polymeric: insensitive to pH, electrolytes and good freeze stability BUT need large amounts of emulsifier to cover droplet. electrostatic: pH dependent, aggregation can occur at high electrolyte conc. small amounts needed. poor freeze stability
Is Lecithin a good emulsifier?
yes! it’s a phospholipid
what is the HLB value
the hydrophilic/lipophilic balance. HLB = 20xMh/M. where Mh is the hydrophilic mass of the molecule and M the whole molecule
what’s the general rule of HLB values
low give W/O emulsions and 7 equal and 8 and over O/W
