Proteins Flashcards
(52 cards)
Is protein solubility linear or non linear?
Is non linear. It is linear only for an ideal solution for example for a NaCl solution. A plateu is then reached when excess.
Are whey protein soluble at every pH?
Yes, however if heated may form aggregate which can be insoluble.
What is the percentage of casein and whey in milk proteins?
80 and 20 % respectively for casein and whey.
What filtration method do we use to separate cream, casein, whey and lactose/salts?
Microfiltration, ultrafiltration, nanofiltration and reverse osmosis respectively.
What are the main types of caseins?
alpha-s1, alpha-s2, beta and kappa.
What happens when caseins are phosphorylated and where does phosphorylation usually occur?
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.
Why caseins forms random coils and not alpha and B sheets and so helical structure
Because of the presence of proline. High amount of proline can hinder alpha and b sheet formation.
What are the two methods to caseins isolation?
Filtration and precipitation
Are casein miscelles soluble in water?
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.
What are the main whey proteins?
- alpha lactoglobulin
- B- lactoglobulin
- serum albumin
How can one obtain more pure whey protein?
By nanofiltration
How can one enrich whey protein with more alpha lactalbumin or B lactoglobulin?
By chromatography + heat precipitation
Which one is more at risk of maillard reactions, WPI or WPC
WPC as it contains more lactose which can react in malliard reactions.
What type of proteins are whey? and gelatin?
Globular and fibrous respectively.
What is the name protein in gelatin and what structure does gelatin produce and why?
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.
What is a downside of plant proteins? Hint: non protein compounds
Anti nutritional factors
What does hydrolysis of protein lead to?
- Decrease allergenicity
- Formation of peptides which all have its own pI.
- Exposure of hydrophobic groups which could lead to aggregation
An intact protein has a degree of hydrolysis of 0 or 100%?
0
How can one calculate degree of hydrolysis, which analytical technique would we use?
With OPA method which analyses number of free amino groups.
Describe V8 mechanism and BLP mechanism.
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.
What happens with heat and cooling of casein miscelles.
Dissociation and reassociation into new miscellar caseins. Calcium and phospate groups that were embedded can also be released.
Will heating of globular proteins always lead to aggregation?
No, in diluted system this may not occur as proteins may not encounter other proteins and thus aggregate.
Does heating lead to unfolding of proteins?
Not necessarily, only at temperature higher than denaturation temperature.
What does denaturation temperature represent?
Temperature at which 50% of protein is unfolded and 50% is in native state. Usually this temp is around 70-80C.
