Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Food Chemistry - FDSC251 > U5 - a + b > Flashcards

U5 - a + b Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Gourmet Food flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what is autoxidation

A

free radical reaction of unsaturated fatty acids with molecular oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

true or false: autoxidation is spontaneous and self sustaining

A

true

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

effects of autoxidation (4)

A
  1. rancidity
  2. loss of functionality
  3. decrease in nutritive value
  4. spoilage - possible toxic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

there are 11 factors affecting autoxidation

A

energy (light and heat), catalysts, double bonds, enzymes, chemical oxidants, oxygen content and types of oxygen, natural antioxidants, phospholipids, fatty acids, mono and di glycerides, polymers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

3 steps of autoxidation

A

initiation propagation termination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is initiation

A

homolytic cleavage of a covalent bond, forming 2 free radicals (the electrons are split evenly)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what 2 things must occur for autoxidation to happen

A
  1. Hydrogen abstracted from fatty acid

2. molecular oxygen present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how is hydrogen abstracted from the fatty acid chain

A 
light/ionizing radiation
heat
metallic cations
enzymes
reactive singlet oxygen 
combination
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

equation for initiation

A

RH –> R. + H.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how long does a free radical last

A

nanoseconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what happens if molecular oxygen isnt present

A

lipid free radicals recombine - no harm done

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is propagation

A

reaction of the fatty acid free radical with molecular oxygen, formation of peroxy radical. self-propagation occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

equations for propagation

A

R. + O2 –> ROO.

ROO. + RH –> ROOH + R.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is termination

A

when 2 free radicals react an unreactive species is formed and the free radical chain stops

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

3 possible equations for termination

A

ROO. + H. –> ROOH
ROO. + ROO. –> ROOR + O2
ROO. + ROOR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

which of the 3 termination reactions is most probable and what does this lead to

A

hydrogen abstraction (ROO. + H. –> ROOH) leading to an accumulation of hydroperoxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

primary products of autoxidation

A

hydroperoxides (#1) and peroxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

true or false: hydroperoxides are the source of rancidity

A

false - they can degrade into what actually forms rancid odors and flavors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

source of rancidity

A

low molecular weight aldehydes, alcohols, ketones, carboxylic acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what happens if propagation is more frequent than termination

A

accumulation of hydroperoxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

are hydroperoxides stable

A

no - they degrade into low molecular weight rancidity molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what 2 methods create rancidity molecules

A
  1. monomolecular

2. bimolecular

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

when does monomolecular dominate and what is its equation

A

early in autoxidation. ROOH –> RO. + .OH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is formed in monomolecular reaction

A

alkoxy radical (RO.) and hydroxy radical (OH.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

how are aldehydes formed

A

chain scission
alkoxy radical steals an electron from the R2to form a double. forms an aldehyde and releases a free radical - propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

how are carboxylic acids formed

A

oxidation of aldehyde

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

how are alcohols indirectly formed

A

reduction of aldedhyde

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

how are alcohols directly formed

A

alkoxy radial steals a hydrogen from R3H to form an alcohol and release a free radical - propagation

29
Q

how are ketones formed

A

hydrogen is abstracted from the radical chain. this is a termination step reaction - free radicals combine; none form

30
Q

when does bimolecular reaction dominate and what is its reaction

A

when ROOH accumulates later in autoxidation. 2ROOH –> RO. + ROO. + H2O

31
Q

what do peroxy radicals prefer to do

A

abstract an H from a fatty acid

32
Q

what do alkoxy radicals prefer to do

A

decompose into aldehydes, ketones, alcohols, carboxylic acids

33
Q

what is the pace of autoxidation in relation to time>

A

slow at first, then fast. monomolecular then bimolecular, so when both alkoxy and peroxy radicals are formed the reaction can propagate more

34
Q

3 methods to evaluate autoxidation

A

peroxide value
TBA test
AV test

35
Q

definition of peroxide value

A

mEq of peroxide oxygen per 1000g fat

36
Q

what does PV measure

A

only hydroperoxides

37
Q

what is the primary autoxidation product

A

hydroperoxides

38
Q

peroxide value method and equation

A

2KI + 2ROOH –> I2 + 2KOH + 2ROH, then measure amount of I2 released by titrating with sodium thiosulfate

39
Q

when does PV rise

A

when the bimolecualar reaction starts

40
Q

when does PV fall

A

when the decomposition of peroxides outpaces their formation

41
Q

when is the use of PV limited

A

when the fat is rancid

42
Q

what must PV be correlated to in order to provide indicator of accessability

A

sensory data - taste panel

43
Q

is there a rancid flavor associated with induction period

A

no - there is no accumulation of hydroperoxides

44
Q

what is does the TBA test measure

A

a secondary breakdown product - malonaldehyde

45
Q

what is malonaldehyde production directly proportional to

A

degree of autoxidation, which is correlated to flavor defects

46
Q

what is malonaldeyde usually attached to

A

proteins since its highly reacive

47
Q

equation for TBA

A

malonaldehyde + 2TBA –> protein + red complex

48
Q

what test is performed on the products of malonaldehyde-protein breakdown

A

spectrophotometry - assess red color produced

49
Q

what can malonaldehyde be directly quantified with?

A

HPLC

50
Q

what is formation of malonaldehyde a function of

A

lipid makeup

51
Q

what reacts in AV

A

p-anisidine reacts with aldehydes

52
Q

what is measured/quantified in AV

A

UV

53
Q

To initiate an autoxidation reaction, hydrogen has to be abstracted from a fatty acid from

a. Carboxylic and
b. Methyl end
c. Double bond within the FA

A

c

54
Q

An alkyl, carbon and hydrogen chain, group singular bonded to oxygen is…

A

alkoxy radical

55
Q

Milli-equivalents of peroxide oxygen per 1000g of fat is…

A

peroxide value

56
Q

The abstraction of a hydrogen converts a fatty acid into…

a. Aldehyde
b. Ketone
c. Free radical
d. alcohol

A

c

57
Q

When a free radical reacts with molecular oxygen it will produce…

a. Peroxy radical
b. Hydroperoxide
c. Alkoxy group

A

a

58
Q

TBA test measures the concentration of…

A

malonaldehyde

59
Q

True or false: the PV increases linearly with time

A

false

60
Q

At low concentrations of hydroperoxieds, the dominant reaction is…

A

monomolecular

61
Q

Aldehydes resulting from the decomposition of the alkoxy radical can produce alcohols by…

A

reduction

62
Q

True or false: the formation of peroxides is infinite

A

false

63
Q

The peroxy radical is formed as a result of …

a. Abstraction of hydrogen from the fatty acid
b. Reaction fatty acid radical with oxygen
c. Both
d. none

A

b

64
Q

Homolytic cleavage results in the formation of…

A

free radicals

65
Q

When the two electron in a cleaved covalent bond are divided equally between the products, the reaction is called…

A

homolytic cleavage

66
Q

True or false: Autoxidation can be sustained in anaerobic conditions

A

false

67
Q

True or false: oils are bottled in dark glass containers to protect them from autoxidation

A

true - oxygen is also replaced with nitrogen

68
Q

The undesirable off-flavors and odors associated with oxidized fats and oils is called…

A

rancidity

Food Chemistry - FDSC251 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions