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Food Chemistry > Lipids > Flashcards

Lipids Flashcards

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1
Q

name a simple and a compound lipid

A

fatty acid, steroids, carotenoids and compound is acylglycerols, phospholipids and waxes. the two first are glycerol plus fatty acids

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2
Q

what is mandatory to declare on foods

A

fat- and part saturated fat, protein, carbohydrates, salt

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3
Q

which bond is it between glycerol and the fatty acids

A

ester bond

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4
Q

which enzyme catalyze synthesis and degradation of trigycerides

A

synthesis by acyltransferase and degradation by lipase

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5
Q

what are the 2 shortenings of omega 3

A

EPA and DHA

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6
Q

what does the n and x stand for in n:x

A

n=number of carbons and x=number of double bonds

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7
Q

T/F the shorter the chain the higher melting point

A

true

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8
Q

what is the soxhlet method

A

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

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9
Q

what is B&D

A

using chloroform:methanlon:water in the ratio 1:2:0 8 to isolate and purify lipids

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10
Q

what is the Saponification value

A

the fatty chain length

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11
Q

what’s the acid value a measure of

A

how much free fatty acids

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12
Q

iodine value?

A

a measure of the no of double bonds

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13
Q

what major compounds does the phospholipid consists of

A

Choline, phosphate, glycerol and fatty acids

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14
Q

what is Lecithin

A

a common phospolipid in egg yolk

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15
Q

for what are phospholipids good for

A

cell membrane and emulisifyers

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16
Q

T/F when fats and oils are processed phospholipids and free fatty acids are removed

A

true

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17
Q

how do you bleach an oil

A

with activated carbon

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18
Q

what is hydrogenation of lipids

A

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

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19
Q

what is the selectivity ratio (SR)

A

k2/k3 which is the ratio k2=linoleic acid to oleic and k3=oleic to stearic. high SR values are preferred

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20
Q

how to make good hydrogenation

A

have enough H and run to completion

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21
Q

what are critical conditions during hydrogenation

A

high temperature (reaction faster than H diffusion) and high catalytic conc. (difficult to saturate catalyst with h)

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22
Q

what is inter-esterification

A

a random redistribution of fatty acids on the glycerol molecule - softer melting characteristics

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23
Q

what is the effect of Benecol

A

blood cholesterol lowering effect. it’s a fatty acid ester of a plant sterol

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24
Q

what is the difference between lipolytic and oxidative rancidity

A

the first is the fatty acid lipolysis (level of free fatty acids) and the last is the reaction between oxygen and fatty acids

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25
Q

what are the food quality changes of lipid oxidation

A

rancid smell and taste, color and texture changes and reduced nutritional value

26
Q

what is created in the first and second step in lipid oxidation

A
  1. alkyl radical (a free radical took H from lipid, LH to L) and 2. peroxy radical (O2 inserted, LOO)
27
Q

what’s the primary, secondary and tertiary products of lipid oxidation

A
  1. 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)
28
Q

what are the 3 possible initiation steps for lipid oxidation

A
  1. 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
29
Q

what is the name of the biological production of hydroxyl radicals

A

Fenton reaction

30
Q

which fatty acids are most prone of lipid oxidation

A

unsaturated

31
Q

what is chain branching

A

the cleavage of hydroperoxide to secondary oxidation products. often volatile. catalyzed by iron/heme or other heavy metal

32
Q

what happens in the termination step of lipid oxidation

A

two radicals react with each other under formation of a stable product

33
Q

are lipid oxidation dangerous

A

probably not. not in the amount we eat, our senses would not let us eat super rancid

34
Q

name some good things about lipid oxidation

A

bleaching of flour, improved dough forming properties, formation of CLA in milk fat

35
Q

name some pro-oxidants

A

metals Fe and Cu, radicals, oxygenase enzymes and reducing systems

36
Q

name some preventive inhibitors of lipid oxidation

A

they either inactivate O2 (catalase, peroxidase, ascorbate, betakaroten)or metals(nucleotides, amino acids, peptides and organic acids).

37
Q

name some antioxidants

A

GSH-px and vitamins such as ascorbate, ubiquinol and Tocoferol. BAH, BHT

38
Q

how does lipid oxidation relate to aw

A

high at low aw then goes down at the lowest at aw 0.4 then goes up

39
Q

name some factors that prevent lipid oxidation

A

light, temp., mincing/oxygen, moisture and pH (lower pH faster oxidation), lipid hydrogenation

40
Q

what are the typical structure of an antioxidant

A

ring structure

41
Q

which are the 2 most common lipid oxidation measures

A

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

42
Q

what are the 3 polymorphic behaviours of fats?

A

alpha, beta prim and beta

43
Q

what is the structure of the three fat crystal structures

A

alpha can rotate freely and are unstable. beta’ is perpendicular and not as movable. beta is most stable and closely packed

44
Q

How does the bilayer look in melted form

A

the methyl terrace and chair structure

45
Q

what is the fat structure difference between alpha, beta’ and beta?

A

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

46
Q

what are the 3 most common fatty acids in cocoa butter

A

stearic acid, palmitic acid and oleic acid.

47
Q

what is the tempering of cocoa butter

A

you lower the temperature 2 times and the beta form develops just below 33 °C

48
Q

name three alternatives to cocoa butter

A

CBE - fats with similar fatty acid composition (palm oil, sheanut) CBR - hydrogenated soya oil/rapeseed oil (the easiest) CBS- fractionated palm kernel oil

49
Q

what is food dispersions

A

a system of discrete particles in a continuous phase

50
Q

what is a colloid

A

a dispersion with particle size between 10 nm and 0.1 mm

51
Q

what are surfactants

A

surface active agents which are either small amphiphilic molecules or polymers

52
Q

what is the action of an emulsifier

A

lowers the interfacial tension up to critical micelle formation where emulsifier causes micelles. it stabilizes the emulsion

53
Q

what is Bancroft’s rule

A

when making a emulsion of oil, water and emulsifier, the continuous phase will become the one in which the emulsifier is best soluble

54
Q

what is the Gibbs-Marangoni effect

A

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.

55
Q

what is the DLVO theory

A

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.

56
Q

describe coalescence

A

it’s the process by which emulsified particles merge together to form a larger particle. starch can prevent this by making liquid more viscous

57
Q

polymeric vs. electrostatic stabilization

A

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

58
Q

Is Lecithin a good emulsifier?

A

yes! it’s a phospholipid

59
Q

what is the HLB value

A

the hydrophilic/lipophilic balance. HLB = 20xMh/M. where Mh is the hydrophilic mass of the molecule and M the whole molecule

60
Q

what’s the general rule of HLB values

A

low give W/O emulsions and 7 equal and 8 and over O/W

Food Chemistry (4 decks)

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