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Food Chemistry - FDSC251 > U4 - a + b > Flashcards

U4 - a + b Flashcards

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1
Q

properties of a fat are a function of…

A
  1. fatty acid composition

2. fatty acid distribution

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2
Q

difference and similarity between lard and vegetable oil

A

similar fatty acid content
different distribution, causing lard to be solid
due to configurations of GS3 and GS2U in lard

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3
Q

characteristic of lard texture

A

grainy. fixed by interesterification

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4
Q

what is G2SU

A

glyceride with 2 saturated and 1 unsaturated fatty acid

oleopalmitostearin. forms large crystals and causes a grainy texture

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5
Q

when is crystal modified lard formed (CML)

A

intraesterification conditions

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6
Q

when is partially modified lard (PML) formed

A

random distribution conditions

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7
Q

when is direct interesterified lard (DIL) formed

A

directed interesterification (GS3)

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8
Q

what is interesterification

A

exchange of fatty acids on the glycerol backbone via heat and a catalyst. occurs between triglycerides

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9
Q

potential catalysts for interesterification

A

tin, lead, zinc, alkali earth metals

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10
Q

difference between interesterification and hydrogenation

A

both change the physical and chemical properties of the lipid, but interesterification doesn’t produce trans fats

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11
Q

interesterification v intraesterification

A

inter - between TGs

intra - within a TG

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12
Q

what happens when interesterification is undergone at lower temperatures ?

A

more saturated long-chain glycerides fractionally crystallize out

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13
Q

random esterification

A

interesterification carried out to equilibrium, assuming random distribution. occurs at low temperatures

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14
Q

directed interesterification

A

interesterification is directed away from its usual random end-point, allowing the fat to crystallize (GS3 crystallizes first)

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15
Q

is chemical interesterification random or directed?

A

random

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16
Q

is enzymatic interesterification random or directed?

A

directed - produces lipids with highly specific compositions for functional uses and mono/diglycerides for emulsifiers

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17
Q

catalyst used at high temperature

A

KOH and NaOH

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18
Q

catalyst used at low temperature

A

NaOCH3

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19
Q

cocoa butter melting point

A

sharp and at body temp

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20
Q

can other fats and oils be modified to produce cocoa butter?

A

yes! good because this reduces the amount of expensive cocoa butter needed

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21
Q

what can be formed as a byproduct from interesterification

A

mono and di glycerides used as emulsifiers

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22
Q

4 analytical methods for modified triglycerides

A

Iodine value
saponification value
gas chromatographic analysis
liquid chromatogroaphy

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23
Q

definition of iodine value

A

mass of iodine in g absorbed by 100g of a fat sample

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24
Q

what 2 things does IV tell us

A

degree of unsaturation and source of oil

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25
Q

IV is directly proportional with…

A

degree of unsaturation
fats are lower
oils are higher

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26
Q

IV is indirectly proportional with…

A

melting point

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27
Q

description of WIJS method

A
  1. ICl + fat –> saturated
  2. KI + ICl excess –> I2
  3. I2 titrated with NaSO3
  4. blank titration
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28
Q

how to calculate IV

A

create a ratio between the grams of iodine needed for 1 molecule of fat (taking # double bonds into account)

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29
Q

catalyst activity is represented as

A

decrease in IV per time

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30
Q

relationship between agitation and hydrogenation

A

more agitation = faster hydrogenation

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31
Q

relationship between catalyst concentration and hydrogenation

A

more catalyst = faster hydrogenation

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32
Q

what is saponification

A

hydrolysis of ester under alkaline conditions

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33
Q

what is saponification value

A

mg of KOH needed to neutralize the FAs released from hydrolyzing 1g of lipid

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34
Q

saponification value equation

A

(56.1 * (B-S) * N)/g

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35
Q

saponification is directly proportional to

A

number of fatty acids

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36
Q

saponification value is indirectly proportional to

A

chain length

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37
Q

method for gas chromatography

A
  1. extract
  2. saponify
  3. prepare methyl ester
  4. chromatograph methyl esters
  5. determine peak areas of fatty acids (retention time)
  6. compare to the response curve of known fatty acids
38
Q

G2SU means…

a. TG with 2 unsaturated fatty acids and one saturated fatty acid
b. TG with 2 short chained fatty acids and one unsaturated fatty acid
c. TG with 2 saturated fatty acids and 1 unsaturated fatty acid

A

c

39
Q

True or false

Intraesterification is an exchange of FAs among TG molecules

A

F

40
Q

the mass of iodine in grams absorbed by 100g of the sample is…

A

iodine value

41
Q

the saponification value of a fat is inversely proportional to the…

A

chain length

42
Q

The saponification value of a fat sample is

a. Directly proportional to the chain length of fatty acids in the sample
b. Inversely proportional to the chain length of fatty acids in the sample
c. Directly proportional to the number of double bonds in the sample
d. Inversely proportional to the number of double bonds in the sample

A

b

43
Q

the rate of hydrogenation reaction is measured by the change of…

a. Saponification value per minute
b. Chain length per minute
c. IV per minute

A

c

44
Q

why don’t fats have sharp melting points

A

complex mix of TGs with unique melting points. composite of these MPs

45
Q

why do fats appear solid at room temperature

A

oil trapped in a crystalline matrix

46
Q

what % of solids are neccessary to make the fat retain solid character

A

10%

47
Q

what is plasticity

A

changes in consistency as a function of temperature

48
Q

what property of fats allows them to have plasticity

A

made of a liquid in a crystalline matrix. thus, the 3D crystal network is held together by weak VDW interactions that constantly dissociate and reform

49
Q

solid-to-liquid ratio is a function of

A

temperature

50
Q

plasticity of a function of

A

solid to liquid ratio

51
Q

what is the plastic range

A

the state a fat is in when it can be deformed readily

52
Q

the plastic range is a function of (2 things)

A

fatty acid composition and distribution

53
Q

difference between margarine and butter

A

margarine - wide plastic range. butter - small plastic range

54
Q

what is polymorphism

A

TGs able to change from one crystal form into another

55
Q

alpha form

A

thin,leaf-like crystals
melting fat the quickly cooling
random packing arrangement
unstable

56
Q

beta prime form

A

remelting and slowly cooling
small and uniform crystals
desirable structure

57
Q

beta form

A

remelting and cooling very slowly
dense, large crystals
large and grainy

58
Q

analytical methods for studying polymorphism

A

x-ray diffraction analysis
microscopic analysis
IR spectroscopic analysis
thermal analysis

59
Q

how to determine solid fat content

A

dilatometry

60
Q

what is dilatometry

A

measurement of the change in specific volume per unit of temperature change

61
Q

dilatometry process

A

measuring the fat expansion as a function of temperature in a reservoir

62
Q

dilatometry curve is a combination of what 3 curves

A
  1. thermal expansion of solid fat
  2. expansion due to change in state
  3. thermal expansion of liquid only
    these 3 are consecutive
63
Q

solid fat index formula

A

x/y * 100 (x is at a certain temperature)

64
Q

how to determine solid fat content

A

NMR - nuclear magnetic resonance

65
Q

NMR process

A
  1. place fat in magnetic field
  2. radiofrequency (RF) pulse delivered perpendicular to field
  3. the H nuclei spins
  4. detect free induction decay (FID) - relaxiation process . since solids relax faster than liquids, comparing the FID time determines the SFC
66
Q

what method is preferred? NMR or dilatometry

A

NMR

67
Q

consitstency

A

apparent hardness at a specific temperature

68
Q

beta prime in shortening

A 
large amount of small air bubbles. 
smaller crystals
whiter, creamier, more tender, smoother
uniform and glossy
better volume and texture of baked goods
69
Q

beta in shortening

A

small amounts of large air bubbles
large clustered crystals
waxy/grainy

70
Q

what crystals are present in natural lard? rearranged? how does the molecular arrangement change

A

natural - beta. more palmatic acid at postion 2

rearranged - beta prime

71
Q

what kind of mixture is margarine

A

water-in-oil emulsion

72
Q

what oils are present in margarine

A

soybean (beta) and hydrogenated cottonseed (beta prime)

73
Q

blending these 2 oils into margarine is desirable because…

A

produces a high polyunsaturated and low/none trans containing product. good spreadability and high temp stability

74
Q

what is tempering

A

process of transforming to the proper polymorphic form

75
Q

what must processors be mindful of when tempering?

A

removing the heat of transformation so that melting and over-transforming dont occur

76
Q

difference between hydrogenated palm kernel oil and randomized hydrogenated palm kernal oil. result of mixing

A

hydrogenated palm kernel oil - hard butter; melts at a higher temp; waxy mouthfeel

randomized hydrogenated palm kernal oil - melts at a lower temp

mixing creates a hard butter that melts in your mouth

77
Q

cocoa butter

A

short melting range
mostly disaturated TGs
polymorphism state determines texture at temperatures

78
Q

small beta crystals in cocoa butter

A

glossy texture. beta prime

79
Q

large, clustered beta crystals

A

chocolate bloom. white spots and dull surface appearance

80
Q

2 examples of oil-in-water emulsions

A

mayo and salad dressing

81
Q

what properties do emulsions have in food products

A

more viscous
more opaque
fatty sensation masked

82
Q

True or false: fat can provide the body with vitamin C

A

false

83
Q

a crunchy chocolate is obtained when cocoa butter forms

a. Small alpha crystals
b. Small beta prime crystals
c. Small beta crystals
d. Large beta crystals

A

c

84
Q

butter has a sharp fat content curve which means

a. It melts quickly
b. It releases flavors quickly
c. None
d. Both

A

d

85
Q

The preferred crystal type in margarine is…

a. Alpha crystals because it gives better spreadability
b. Beta prime crystals because it give better spreadability and creamy mouthfeel
c. Beta crystals because they give a desirable degree of solidness

A

b

86
Q

fats don’t have sharp melting points because

a. Consist of different TGs with different MPs
b. Have a 3D network of crystals delaying the melting of some fat crystals
c. None
d. Both

A

a

87
Q

Interesterified TGs can be fractionated by controlling the …

A

temp

88
Q

The change in consistency as a function of temperature is…

A

plasticity

89
Q

True or false: Beta prime crystals are preferred for chocolate

A

false; beta

90
Q

The technique that is based on the measurement of the change in specific volume per unit temperature is called…

A

dilatometry

91
Q

When fat is cooled quickly it forms thin, leaf-like crystals. This forms…

A

alpha crystals

Food Chemistry - FDSC251 (10 decks)

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