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Food Protiens > lecture 7 > Flashcards

lecture 7 Flashcards

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1
Q

what is acytlation?

A

a rxn where an acetyl group (CH₃CO) is added to a protein, usually to specific amino acids like lysine( ε-amino group) or the N-terminal of a protein. It replaces the positive amino group with a negative group→result is protien is more negatively charged

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2
Q

what are the effects of acyetlation?

A

Improves solubility, as the addition of a bulky group, increases repulsion between protiens. It inhibits gelation. And it shifts the pI of the protien to a lower pH meaning it will better dissolve in acidic conditions

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3
Q

what is succinylation

A

a rxn where a succinyl group (a molecule with two carboxylic acid groups) is added to a protein, usually attaching to amino acids like lysine, histidine, cysteine, tyrosine, serine, or threonine.

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4
Q

what are the effects of succinylation?

A

This reaction increases protiens negative charge and enhances repulsion as well as increases the hydrophilic nature if the protien. This increases solubility. Improves emulsifying and foaming. As it enhances gelation due to hydrophilic/hydrophobic balance changing and since there are many functional OH groups allows for more crosslinkinh. And it decreases digestability and bioavability

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5
Q

what is phosphorylation?

A

is a rxn where a phosphate group is added normally from phosphoric acid,this phosphate group will be covalently attached to the protien typically at a OH group called o phosphorylation or amino group(NH2) called N-phosphorylation

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6
Q

what are the effects of phosphorylation?

A

It introduces a negative charge, which shifts the isoelectrical point to a lower pH. It increases solubility because of increased polarity. This also allows for these amino acids to form cross links, enhancing the stability of gels

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7
Q

what are the sensitivities of pH of O-phosphorlyated resides vs N-phosphorlated?

A
  1. o= stable at acidic pH
  2. stable at basic pH, can be dephosphorylated in acidic pH
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8
Q

how are carboxyamidomethyl formed?

A

The protien is reacted with iodacetamide at a pH of 8-9, and acetamide will be added which stabilizes the thiol group, preventing disulfide bonds from forming.

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9
Q

what are CAM modiifications used for?

A

Crucial for identfication and quantification of protien for anylasis as it prevents formation of disulfide bonds, which make the protien easier to denature and digest when working with them in experiments

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10
Q

what happens during the formation of lysinoalanine?

A
  1. protiens are exposed to alkaline conditions and heated, the amino acids will undergo chemical changes
  2. intermediate formations: serine/cystine residues reaction to form unstable intermediates
    1. serine looses water to form Dehydroalaline
    2. cystine looses hydrogen sulfide to form dhydroalaline as well
  3. cross linking with lysine: The ε-amino group of lysine reacts with dehydroalanine to form lysinoalanine through a covalent bond.
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11
Q

what is the result of lysinoalanine formation?

A

Reduces protien quality as it reduces digestability and bioavability. It is also a saftey concern because it can have potential toxic effects it too high

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12
Q

what is alkylation?

A

is a reaction where an alkyl group (methyl, ethyl.) is added covantely to the side chain of an amino acid . This is irreversabile

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13
Q

what is the result of alkylation

A

Impairs nutritional qulaity as it reduces the avaibility of essential amino acids like lysine and cystine for digestability and bioavilibility. They are more resistant to digestive enzymes. they also improve emulsfying as the added groups are better at stabilization due to increased hydrophobicity. In terms of solubility it could decrease or increase solubility based on size of group and nature of group. Overall since they are hydrophobic and the larger they are, they will decrease solubility.

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14
Q

what are the two types of alkylation?

A

reductive and non reductive (malliard)

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15
Q

what are the steps of reductive alkylation?

A
  1. addition of an alkyl group from an aldehyde/ketone will react with α- or ε-amino group at a pH of 9 this will form a schiffs base
  2. reduction: a reducing agent like borohydride or cyanoborohydride this will “lock in” the schiffs base and it cannot keep going in the malliard rxn
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16
Q

how is a disulfide bond formed and broken

A

formed through oxidation which links thiol groups on 2 cystine residues. To break this very strong bond it is done via reduction where a free cys is added

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17
Q

what is the benefit of disulfide bonds?

A

enhances heat stability, viscosity, foaming and gelling properties

18
Q

what is chemical crosslinking?

A

it is the covalent attachment of one functional group of a side chain to another molecule which can be intra or intermolecullary

19
Q

what is the benifit of chemical crosslinking?

A

it makes it possible to stabilize tertiary and quaternary structures which improves stabilization of foams, gels, and emulsions

20
Q

explain the cross linking of acidic and basic amino acids

A

when heated lysine can form covalent cross links with aspartic/glutamic acid which forms an isopeptide bond

21
Q

what is schiffs base (formula)

A

R1-CH=N-R2

22
Q

in short what is the malliard reaction

A

It is a reaction that occurs during cooking between amino acids and reducing sugars(have aldehyde free), which involves a series of complex reactions that result in the browning of food and the creation of flavours

23
Q

what are the steps of the malliard reaction?

A
  1. formation of schiffs base: a reducing sugar reacts with an amino group foroming a schiffs base
  2. amadori rearrangement: the schiffs base undergos rearrangment which forms the amadori compound (ketoamine), which is a more stable intermediate
  3. decomposition: the amadori compounds break down by dehydration and fragmentation into reactive intermediates like dicarbonyl compounds like HMF, pyruvate aldehyde. Which begin to form flavours
  4. formation of flavor and brown pigments: the reactive intermediates condense and polymerize to form melanodins which are responsible for the brown pigments. These reactions also form flavor compounds
24
Q

what is the effect of substrate concentration on enzyme activity?

A
  • At low substrate concentrations, the reaction rate (V₀) increases almost linearly as more substrate binds to the enzyme.
  • At high substrate concentrations, the enzyme becomes saturated, and the reaction rate approaches a maximum velocity (Vmax).
25
Q

what are the numbers for the corresponding classes of enzymes?

A
  1. oxireductases
  2. transferases
  3. hydrolases
  4. lysases
  5. isomerases
  6. ligases(synthestases)
26
Q

what is the effect of enzyme concentration on enzyme activity?

A

As enzyme concentration increases, the reaction rate also increases, assuming the substrate is not limiting.

27
Q

what is the effect of temperature and pH on enzyme activity?

A

Enzymes have an optimum temperature and pH

where they function best. Beyond these conditions:

  • Too high a temperature can cause denaturation.
  • Extreme pH values can disrupt the enzyme’s structure or active site.
28
Q

what is michealis-menten equation

A

V0=Vmax x [s]/Km + [S]
- V₀: Initial reaction velocity.
- Vmax: Maximum reaction velocity when all enzyme active sites are occupied.
- [S]: Substrate concentration.
- Km: Michaelis constant, the substrate concentration at which the reaction velocity is half of Vmax.

29
Q

what does a high and low Km indicate?

A
  • A low Km indicates high enzyme-substrate affinity.
  • A high Km indicates low enzyme-substrate affinity.
30
Q

what reactions can also be done with the help of an enzyme

A
  • hydrolysis
  • glycosylation
  • phosphorlyation
  • methylation
  • acylation
  • cross linking
31
Q

describe glycosylation

A

Is a reaction between protiens and carbs, they attach either at the α- or ε-amino group of a protien. It is essentialy alkylation but the alkyl being added is a sugar molecule

32
Q

what are the effects of glycosylation

A

Increases solubility as a sugar increases hydrophilicity. It improves emulsififaction because of the changes to the hydrophilic-hydrophobic balance. It also reduces digestability.

33
Q

what is glycosylation a part of?

A

part of reductive alkylation or malliard, but if its malliard there must be no reductive agent

34
Q

what are transgluatminase

A

used industrially to cross link protiens. catylzes the acyl-transfer rxn between lysine and amide group of glutamine

35
Q

what are the roles of transgulatminase

A

used to produce stable gels/films and can be used to increase lysine content since the bond formed is digestable

36
Q

what is enzymatic hydrolysis

A

this is the process where enzymes break down larger molecules into smaller ones by the addition of water

37
Q

what is the result of enzymatic hydrolysis?

A

could increase solubility, emulsification and foaming. But it reduces viscosity as it cut chains

38
Q

what are common uses of enzymes in food products?

A

lactase. Proteases in meat tenderizes

39
Q

what is the purpose of enzyme immobilazation??

A

enzymes traditionally where denatured to stop their activity in foods and that meant a new enzyme was to be added every new batch. But enzyme immobilation allows the seperation of enzymes from food, so they can be reused.

40
Q

how is enzyme imbolization done?

A

enzymes are attached to surface/particle by covalent bonding, crosslinking, adsoprtion, encapsulation,entrapment

  1. batch method: enzymes are immobilzed on insoluble particls and added directyly to reaction mixture for required time and then they are strained out
  2. flow columns: enzymes are immbolized on surface or particles inside tubes where substrates flow continiously, and the activity ends when liquid exits the tube

Food Protiens (9 decks)

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