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FDSC251 (Food chem 1) > Lipids lecture 6 > Flashcards

Lipids lecture 6 Flashcards

1
Q

what is catalyst activity?

A

decrease in iodine number per unit of time during hydrogenation under a specific set of conditions

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2
Q

what is the iodine number?

A

iodine number:

  • number of grams of iodine absorbed by 100 grams of fat
  • iodine number indicates degree of unsat of the FA residues of the glycerides (b/c unsat FA reacts with iodine)
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3
Q

what is selectivity?

A

preferentially hydrogenating more highly unsaturated FA

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4
Q

what does SR= C(18:2)/C(18:1)-12.2 mean?

A

Selectivity ratio to produce C18:0

means that stearic acid is produced 12.2 times faster from linoleic acid than from oleic acid (b/c catalyst has a higher affinity for highly unsat FA)

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5
Q

2 types of hydrogenation?

A

partial and complete

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6
Q

what are factors that affect reaction rate of hydrogenation?

A
  1. nature of substance to be hydrogenated
  2. nature and conc of catalyst
  3. rxn pressure
  4. rxn temp
  5. degreeeo f agitation
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7
Q

steps in hydrogenation of oils?

A 
1 transfer/diffusion
2 absorption
3 hydrogenation/isomerization
4 desorption
5 transfer
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8
Q

what are transfer/diffusion and adsorption critical for?

A

controlling the degree of isomerization and selectivity of rxns

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9
Q

what is transfer and diffusion?(hydrogenation)

what is it important for?

A

transfer: transferring reactants and products to and from liquid oil phase and outside surface of the catalyst
diffusion: diffusion of reactant into and out of the pores of the catalyst

both are important for controlling the degree of isomerization and selectivity of rxns

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10
Q

ratio to express selectivity?

A

K (lo) / K (o) = rate of hydrogenation of linleate relative to that of oleate

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11
Q

what determines selectivity for hydrogenation?

A
  1. geometric configuration of the catalyst

2. chemical/physical characteristics of catalyst

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12
Q

calculate iodine number of linoleic acid, C17H31COOH.

A

Molecular weight of linoleic acid = 18(12) + 32(1) + 2(16) = 280 g /mol

Molecular weight of iodine = 2(127) = 254 g/mol

Linoleic acid has 2 double bonds per molecule (from last problem).

280 grams of fat reacts with 2 x 254 g of iodine = 508 g iodine

100 grams of fat reacts with 508/280 = 181

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13
Q

0.01 moles of linoleic acid reacts with 5.1 g of iodine. Determine the number of double bonds present in the fatty acid.

A

Moles iodine = (5.1 grams)(1 mole iodine / 254 grams of iodine) = 0.020 moles I2
This implies a ratio of 0.01 mol linoleic acid : 0.020 mole I2

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14
Q

in hydrogenation of soybean oil, what does linolenic become?

what starts as the highest percent before hydrogenation?

A

linolenic –> linoleic –> oleic –> stearic

linoleic is highest percent

(refer to chart)

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15
Q

describe copper catalyst

A
  • copper-chromium (CuO 50% + Cr2O3 40% + BaO 10%)
  • high selectivity for linolenic acid (KLn / KLO = 10)
  • almost infinite selectivity for linoleate
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16
Q

hydrogenation of FA in TG is not a function of….

A

their location

whether the DB is in 1st, 2nd, or 3rd position doesn’t matter

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17
Q

what is the lifetime of a catalyst

A

how long a catalyst will remain active and useful

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18
Q

what is AOCS

what is their method of determining catalyst activity?

A

american oil chemists society

catalyst activity is determined by the time required to hydrogenate soybean oil to an IV of 80 from 120 at 350 deg F, 20psig, 0.05% catalyst conc compared to time needed using AOCS standard catalyst under the same conditions

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19
Q

does olive oil of hydrogenated soybean oil have lower IV?

A

olive oil has lower IV b/c has more monounsaturates

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20
Q

what are factors affecting hydrogenation?

A

independent variables

  1. pressure
  2. temp
  3. agitation
  4. catalyst concentration

dependent

  1. trans FA
  2. selectivity ratio
  3. hydrogenation rate
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21
Q

how does increased pressure and temp effect trans unsaturation of soybean oil?

A

as pressure INCREASES, trans FA DECREASES

as temp INCREASES, trans FA INCREASES

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22
Q

how does pressure, temp and catalyst conc effect selectivity ratio?

A

as pressure INCREASES, selectivity ratio DECREASES

as temp INCREASES, selectivity ratio INCREASES

as catalyst conc INCREASES, sr INCREASES

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23
Q

how does agitation, pressure, temp affect selectivity ratio?

A

as agitation INCREASES, sr DECREASES

as pressure INCREASES, sr INCREASES

as temp INCREASES, sr INCREASES

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24
Q

how does agitation and catalyst conc affect rate of hydrogenation?

A

as catalyst conc increases, H rate increases

as agitation increases, H rate increases

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25
Q

another use for interesterification

A

production of monoglycerides used as emulsifiers

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26
Q

analytical methods for modified TG?

A

saponification value

iodine value

gas chromatographic analysis for FA

liquid chromatography

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27
Q

what is the saponification value?

A

number of milligrams (mg) of potassium hydroxide (KOH) to saponify 1 g of the fat/oil sample.

expressed by weight, not moles (b/c the substance is not always known or pure)

28
Q

what is saponification?

A

hydrolysis of ester under alkaline conditions

29
Q

how to determine saponification value?

A
  1. Weigh 5 g of fat in 250-mL Erlenmeyer.
  2. Add 50 ml KOH (0.5 N) to Erlenmeyer.
  3. Boil to saponify fat.
  4. Titrate with HCl (0.5 N) using phenolphthalein.
  5. Conduct blank determination.

Saponification value = 56.1 × (B – S) × normality of HCl / g of sample

B = mL of HCl required by blank to reach phenolphthalein endpoint.

S = mL of HCl required by sample to reach phenolphthalein endpoint.

Molecular weight of KOH = 56.1

30
Q

how to calculate AMW of a simple TG?

A

AMW = 41 + 3 x (MWFA -1)

31
Q

how to calculate AMW of simple and mixed type TG (has 2 FA: R1 and R2)?

A

AMWTG = 41 + 3 x [(xR1 x MWFAR1 + xR2 x MWFAR2 ) -1]

32
Q

steps of GC analysis for FA?

A
  1. Extract fat.
  2. Saponify (hydrolysis under basic condition).
  3. Prepare methyl esters (CH3ONa).
  4. Chromatograph methyl esters.
  5. Determine peak areas of fatty acids.
    Fatty acids are identified by retention time.
  6. Compare with response curve of fatty acid standards.
33
Q

what does higher IV usually indicate?

A

oils and lower value fats

34
Q

approximate IVs of animal fats, non drying oils, semi drying oils, drying oils?

A

Animal fats (butter, dripping, lard): IV = 30 – 70

Non-drying oils (olive, almond): IV = 80 - 110

Semi-drying oils (cottonseed, sesame, soya): IV = 80 - 140

Drying oils (linseed, sunflower): IV = 120 - 200

35
Q

what methods are used to determine IV?

A

Wijs or Hanus methods

36
Q

describe Wijs method?

A

DB + ICl –> Cl-CH-CH-I

ICl + KI –> KCl + I2

I2 + 2 Na2S2O3 –> Na2S4O6 + 2 NaI
+KI

37
Q

oils that prefer beta type?

beta prime type?

A 
beta:
Coconut oil 
Corn oil 
Olive oil 
Lard
Palm kernel oil
beta prime:
Cottonseed oil 
Herring oil 
Menhaden oil 
Milk fat
Palm oil
38
Q

what are important characteristics of shortenings?

what do they depend on?

A
  1. incorporation of air, plasticity and consistency
  2. solid-liquid ratio

depends on:

  1. polymorphic forms of the fats
  2. method of prep
39
Q

what does plasticity, consistency, solid liquid ratio depend on?

A

melting range

needs proper tempering to form mixed crystals needed for a broad melting range

40
Q

what size air bubbles do beta prime have vs beta?

A

beta prime: large amount of small air bubbles

beta: small amount of large air bubbles

41
Q

describe beta prime crystal shortening

A

Small crystals

Whiter, creamier, more tender, smoother texture

Uniform and glossy texture

42
Q

describe beta crystal shortening

A

Large clustered crystals

A waxy or grainy texture

43
Q

role of beta prime crystal shortening in baking?

A

incorporation of an abundant quantity of small air bubbles in batters for good volume,
texture and tenderness of baked goods.

44
Q

natural vs rearranged lard?

A

natural: palmitic acid is at 2 pos (64%)
rearr: palm acid at 2 pos (24%)

45
Q

steps of lard conversion from beta to beta prime?

A

Interesterification

Interesterification and hydrogenation

Winterization (destearinization)

Addition of cottonseed oil and/or tallow flakes (beta- prime)

46
Q

define plasticity

A

changes in consistency as a function of temperature.

47
Q

define consistency

A

apparent hardness at a temperature

48
Q

oils in margarine?

A

soybean (Beta) and hydrogenated cottonseed oil (beta prime)

49
Q

what happens when beta prime becomes beta in chocolate?

A

white spots and dull surface

50
Q

what is tempering?

A

A process which permits transformation to the proper polymorphic form.

During crystallization, the heat of transformation must be removed to avoid melting and a later conversion into large beta crystal.

51
Q

how does the FA chain length affect MP of TG?

A

Melting point of TG increases as FA chain length increases

52
Q

is natural and randomized lard beta or beta’ ?

A

natural: beta
randomized: beta’

53
Q

what does randomization of lard improve?

A

plastic range

makes it a better shortening than natural lard

54
Q

how to produce High polyunsaturated content and low-to-zero trans-acid containing margarines?

A

by interesterifying a blend of liquid oil and a fully hydrogenated oil.

55
Q

describe hydrogenated palm kernal oil

A

hard butter melting at 46 C and produces a waxy feel in the mouth.

On randomization, its melting point is reduced to 35 C. By blending hydrogenated palm kernel oiland its randomized product, a whole series of hard butters with highly desirable melting qualities (rapid melt in mouth) are obtained

56
Q

what happens to SCI of Hydrogenated Soybean Oil and Palm Stearine when temp increases? Before and after interesterification?

A

SCI decreases as temp increases

before: more gradual

57
Q

what happens to SCI of cocoa butter when temp increases?

how does SCI compare before and after interesterification?

A

SCI decreases

before interesterification: sharper decrease

after: more gradual decrease

58
Q

major uses of fats?

A

shortenings

margarines

confectionary fats

59
Q

role of shortening in baking?

A

reduces elasticity of dough

makes pastry more tender/ flaky

60
Q

fats w/ higher levels of unsat FA have… ____ shortening power

A

greater shortening power

61
Q

what does lard shortening properties depend on?

A

dominant crystal form

solid fat content

62
Q

describe margarine

A

water(~20%)-in-oil emulsions, with some milk solids, which have extensively replaced butter.

may consist of:
hydrogenated fats
• mixture of hydrogenated fat(s) and unhydrogenated oil(s)
• mixture of interesterified fat(s) and unhydrogenated oil(s), or
• mixture of unhydrogenated fats.

63
Q

how is margarine made?

A

High polyunsaturated content and low-to-zero trans-acid containing margarines are produced by interesterifying a blend of liquid oil and a fully hydrogenated oil.
Mixture is fed into a scraped-surface heat exchanger, which partially solidifies the material.
Product may be tempered to allow for crystallization in a manner that gives good plasticity and spreadability.

64
Q

properties of confectonary fats

A

Has narrow melting point range and contains about 80% disaturated triglycerides:
20% SOS - stearic, oleic and stearic 55% POS - palmitic, oleic and stearic
5% POP - palmitic, oleic and palmitic
advantage:
-solifidies fast = can be used as enrobing fats but melts at body temp

65
Q

describe emulsions

properties of emulsions?

A

Emulsifiers stabilize and reduce the interfacial tension between the hydrophilic and hydrophobic constituents

properties: must have both hydrophilic and hydrophobic groups in its molecular structure. to reduce surface tension (seen on MonoGC and phospholipids)

66
Q

properties of emulsions after emulsified

A

more viscous, opaque and thefattysensationis masked.

FDSC251 (Food chem 1) (8 decks)

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