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Food Structuring > Proteins > Flashcards

Proteins Flashcards

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1
Q

Is protein solubility linear or non linear?

A

Is non linear. It is linear only for an ideal solution for example for a NaCl solution. A plateu is then reached when excess.

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2
Q

Are whey protein soluble at every pH?

A

Yes, however if heated may form aggregate which can be insoluble.

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3
Q

What is the percentage of casein and whey in milk proteins?

A

80 and 20 % respectively for casein and whey.

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4
Q

What filtration method do we use to separate cream, casein, whey and lactose/salts?

A

Microfiltration, ultrafiltration, nanofiltration and reverse osmosis respectively.

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5
Q

What are the main types of caseins?

A

alpha-s1, alpha-s2, beta and kappa.

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6
Q

What happens when caseins are phosphorylated and where does phosphorylation usually occur?

A

Phosphorylation gives a charge to caseins ranging from 0 to -2 and can low pI of caseins. Usually alpha-s1 and s2 are the most phosphorylated.

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7
Q

Why caseins forms random coils and not alpha and B sheets and so helical structure

A

Because of the presence of proline. High amount of proline can hinder alpha and b sheet formation.

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8
Q

What are the two methods to caseins isolation?

A

Filtration and precipitation

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9
Q

Are casein miscelles soluble in water?

A

Yes, because of electrostatic repulsion and presence of carbohydrate moiety on outside which is postively attracted to water. However they are not so easily soluble.

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10
Q

What are the main whey proteins?

A
  1. alpha lactoglobulin
  2. B- lactoglobulin
  3. serum albumin
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11
Q

How can one obtain more pure whey protein?

A

By nanofiltration

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12
Q

How can one enrich whey protein with more alpha lactalbumin or B lactoglobulin?

A

By chromatography + heat precipitation

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13
Q

Which one is more at risk of maillard reactions, WPI or WPC

A

WPC as it contains more lactose which can react in malliard reactions.

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14
Q

What type of proteins are whey? and gelatin?

A

Globular and fibrous respectively.

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15
Q

What is the name protein in gelatin and what structure does gelatin produce and why?

A

Main protein is tropocollagen. Gelatin form triple helix strucutre which are possible due to the presence of proline which distrupts formation of alpha helix and b sheets.

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16
Q

What is a downside of plant proteins? Hint: non protein compounds

A

Anti nutritional factors

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17
Q

What does hydrolysis of protein lead to?

A
  1. Decrease allergenicity
  2. Formation of peptides which all have its own pI.
  3. Exposure of hydrophobic groups which could lead to aggregation
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18
Q

An intact protein has a degree of hydrolysis of 0 or 100%?

A

0

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19
Q

How can one calculate degree of hydrolysis, which analytical technique would we use?

A

With OPA method which analyses number of free amino groups.

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20
Q

Describe V8 mechanism and BLP mechanism.

A

V8, called one-by-one-mechanism hydrolyses an entire protein before moving to the next
BLP, called zipper-mechanism, hydrolyses a specific bond in each protein, and then moves to next. BLP will show a faster decay in intact protein concentration.

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21
Q

What happens with heat and cooling of casein miscelles.

A

Dissociation and reassociation into new miscellar caseins. Calcium and phospate groups that were embedded can also be released.

22
Q

Will heating of globular proteins always lead to aggregation?

A

No, in diluted system this may not occur as proteins may not encounter other proteins and thus aggregate.

23
Q

Does heating lead to unfolding of proteins?

A

Not necessarily, only at temperature higher than denaturation temperature.

24
Q

What does denaturation temperature represent?

A

Temperature at which 50% of protein is unfolded and 50% is in native state. Usually this temp is around 70-80C.

25
Q

Why proteins do not denature in spray drying?

A
  1. Water evaporation cools particle and so particle does not witness actual temperature.
  2. At lower aw, denaturation temperature increases.
    However, some parts of some particles may get more heat damaged and aggregate. This can be later removed by filtration.
26
Q

What is foam stability?

A

Describe as time for 50% of the foam to collapse.

27
Q

Is there a non-linear or linear relation between the adsorbed amount of protein and surface pressure?

A

Non-linear

28
Q

Is the initial increase in surface pressure linear or non linear to protein concentration?

A

Linear.

29
Q

Does heating and exposure of hydrophobic groups always lead to faster adsorption kinetics?

A

No. For example, lysozyme heated for 30,60,90 min did not show difference in adsorption kinetics even though higher heating times showed better foaming stability and more hydrophobicity present.

30
Q

What is the effect of particle shape on foam stability?

A

Spherical shapes stabilize better while square shape can lead to dewatting and coalescence and loss of volume.

31
Q

What is the critical protein concentration?

A

The concentration where protein is in excess and drople size does not decrease any more.

32
Q

How can one differentiate between flocculates and coalescence?

A

If by adding SDS the average particle size change (decreases) then it was flocculates otherwise coalescence.

33
Q

When will flocculation occur?

A

At pH=pI

34
Q

Why algea does not show clear isoelectric point?

A

Because of the presence of polysaccharides. The negative polysaccharide can interact with postive protein and form complexes. This presence of polysaccharide can then create steric hindrance against flocculation.

35
Q

What can happen when ionic strength is increase in presence of complexes of polysaccharide protein.

A

This complexes can change and even dissociate as the charges get screened.

36
Q

Why protein are not effective thickeners?

A

Because of their small size. Polysaccharide are much more efficient.

37
Q

What are the three ways protein can aggregate?

A
  1. Heat induce folding
  2. Change pH or ionic strength
  3. Hydrolysis
38
Q

What type of gel are gelatin gels and what does their melting temperature depends on?

A

They are thermoreversible gels and Tm depends on the amount of triple helices.

39
Q

Is denaturation temperature of protein constant?

A

NO

40
Q

At what pH is denaturation temperature maximal?

A

at pH=pI

41
Q

Is aggregation an instantaneous step?

A

No

42
Q

What are the two steps for protein gelation?

A

Unfolding and aggregation

43
Q

What type of gels can be made with protein?

A

Heat set gel and cold set gel which include heating leading to aggregation but no gelation and subsequent decrease of pH to induce gel. Or gel induce by hydrolysis of proteins and decrease in pH.

44
Q

Is the gel transparent or turbid in case of proteins with linear aggregates?

A

Transparent. Turbid is in presence of branched aggragate or random aggregate.

45
Q

How can disulphide bridges increase gel strength?

A

Reshuffling of disulphide bridges after heating can occur which go from being withing the protein to be within different proteins. This will lead to increase gel strength.

46
Q

Why do hydrolysates form gels at higher pH compared to their native protein?

A

Because since their is no clear pI and more hydrophobic groups are present then gels can be induced also at higher pH.

47
Q

What is the protein conversion factor?

A

6.25.

48
Q

What does SDS do to the charges in proteins?

A

It masks them so that all protein has similar charge to mass ratio.

49
Q

What does SDS do?

A
  1. binds to proteins
  2. causes dissociation of non covalent complexes
50
Q

Why are reducing condition used in SDS-page

A

to break disulphide bridges.

51
Q

In size exclusion chromatography are large particle or small particle expelled first?

A

Larger

52
Q

Is size exclusion chromatography performed under reducing conditions?

A

No, under native condition meaning that structures such as casein micelles or any aggregates will not dissociate under these conditions.

Food Structuring (9 decks)

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