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Nutrition Semester 1 > BMS1064: Wk7 - Proteins > Flashcards

BMS1064: Wk7 - Proteins Flashcards

1
Q

What is the primary structure of proteins?

How are peptides different to proteins?

A

Primary structure: the sequence of AAs in a polypeptide chain

Long chains of AAs (with amine and carboxyl groups).
R group differs between AAs, giving polar, non-polar and +/- charge characteristics.

Peptides = 50 AAs or less
Proteins = More than 50 AAs

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2
Q

Describe the secondary structure of proteins.

A

Polypeptide folds as a result of hydrogen bonding between local amino acids.

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3
Q

Describe the tertiary structure of proteins.

What are the different types?

A

Further folding of secondary structure as result of bonding between peptides/polypeptide regions.

LINEAR:
- structural and mechanical elements
- Connective tissue (collagen in tendons, cartilage and bone)

GLOBULAR:
- involved in transport and dynamic functions.
- soluble in aqueous environment (hydrophobic AAs inside and hydrophilic outside).

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4
Q

Describe the quaternary structure of proteins.

A

Two or more polypeptides bound together. (e.g. haemoglobin)

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5
Q

What is the isoelectric point of a protein?

A

The pH at which their net charge is zero.

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6
Q

What are the 3 classifications of proteins?

A

Simple proteins = AAs only
Conjugated proteins = AAs + prosthetic group
Derived proteins = modified by chemical or enzymatic treatment

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7
Q

What are the structural properties of proteins in food?

A
  1. Formation of gels (gelation)
  2. Stabalise emulsions and foams
  3. Form films
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8
Q

What are the effects of denaturing proteins (for food)?

A

Loss of solubility and activity
Changes in functional properties
- enhanced gel formation
- enhancedn stability for emulsions
- elastic films

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9
Q

What is gelation / gel formation?

A

The association or cross linking of the protein chain to form a 3D network that traps or immobilises the water within it to form a rigid structure.

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10
Q

Looking at globular and fibrous protiens, is gelation reversible or irreversible?

A

GLOBULAR proteins unfold on heating and the denatured chains aggregate to form thermally IRREVERSIBLE gels

FIBROUS proteins are able to form thermally REVERSIBLE gels (e.g gelatine from collagen).

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11
Q

What are emulsions?

A

A mixture of two liquids that normally don’t mix (e.g. oil and water).

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12
Q

_______ from milk and eggs are commonly used to stabalise oil-in-water emulsions and foams.

How do they do this?

A

Protiens

INTERFACIAL PROPERTIES
- Able to adsorb at the oil-water and air-water interfaces, preventing aggregation
- Small enough to diffuse to the interface at fast rate.
- Large enough to provide enough points of contact and increase the overall energy of adsorption.

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13
Q

What affects interfacial activity?

A
  • Molecular size
  • Conformation (structure)
  • Amino acid composition
  • pH and solvent composition
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14
Q

What are the benefits of using proteins to form edible films on food?

What are examples of some proteins that can form films?

A
  • Barrier to moisture, O2 and CO2 - enhance shelf-life and appearance
  • Biodegradable packaging
  • Improve mechanical handling properties (size, texture etc)

e.g. Gelatine, whey, soy, corn and wheat gluten

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15
Q

Name 5 enzymes used in food processing.

(Catalytic properties of proteins in food)

A

Invertase
Isomerase
Lipoxygenase
Protease
Lactase

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16
Q

What does the enzyme Isomerase do in food science?

Why is this beneficial?

A

Converts glucose to fructose.

Fructose from corn is sweeter than glucose.
Corn syrups = mixture of fructose and glucose.

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17
Q

What does the enzyme invertase do?

Why is this beneficial in food science?

A

Converts [sucrose] –> [glucose and fructose].

Reduces sugars for confectionary as there are more stable and less likely to crystalise.

18
Q

What does the enzyme lipoxygenase do?

What are the desriable and undesirable results of it being used in food science?

A

Converts Unsaturated FAs -> FA hydroperoxides.

Improves dough and flavour of bread. (desirable)
Causes fat rancidty (undesirable)

19
Q

How are proteases used in food science?

A

Meat tenderization.
Cheese making.
Flavouring

20
Q

How is lactase used in food science?

A

To convert lactose -> galactose and glucose

Makes food more digestable for those who are lactose intolerant. (e.g. lactase added to milk)

21
Q

What are the protein chemical reactions in food? (4)

A
  1. Carboxyl group reactions
  2. Amino group reactions
  3. Thiol group reactions
  4. Other reactions between amino acids (e.g. discolouration in low acid, high protein products and oxidation during freezing)
22
Q

How can carboxyl group reactions be used in food science?

A

To decarboxylate histadine into histamine.

(Histadine -> food poisoning, allergic reactions)

23
Q

How can amino group reactions be used in food science?

A

Acetylation increases the solubulity of proteins -> emulsions

Formation of nitrosamines (nitrates added in meat curing - flavour, colour, protection from bacteria)

Maillard browining - reaction with sugars giving desirable colour and flavour of bread, meats and coffee beans when toasted/cooked/roasted.

24
Q

What are the cons of carboxyl and amino group reactions?

A

AAs are modified, becoming unavailable.

Production of toxic/carcinogenic compounds.

25
Q

How are Thiol group reactions useful in food science?

A

Formation of disulphide bonds - increases elasticity of dough and improves texture.

26
Q

What are the 3 phases of milk?

A

STABLE EMULSION - Fat globules

COLLOIDAL SUSPENSION - casein, whey

TRUE SOLUTION - lactose, water

27
Q

What are caseins?

A

The dominant proteins found in milk. They carry a lot of calcium.

We have the capability of separating these proteins, resulting in a wide array of functional ingredients.

28
Q

list the casein-based ingredients:

A
  • Skimmed milk powder (SMP)
  • Acid Casein
  • Rennet Casein
  • Caseinate
  • Milk protein concentrates
  • Phosphocasein

All ingredients obtained as powder.

29
Q

How is Skimmed milk powder obtained from caseins?

A

Centrifugation

30
Q

How is Acid casein obtained?

A

Decrease in pH - caseins self-aggregate

31
Q

How is Rennet casein obtained?

A

Through the action of Chymosin - caseins self-aggregate

32
Q

How is caseinate obtained?

A

Neutralisation of acid/rennet casin through alkali addition.

33
Q

How are milk protein concentrates obtained?

A

Membrane technology

34
Q

How is Phosphocasein obtained?

A

Microfiltration

35
Q

What are the functional uses of casein ingredients in food science? Which ingredients are involved?

A

Acid gels - Na/Ca caseinate, phosphocasein and SMP - e.g. yoghurts

Recombined milk products - SMP (due to stability at high temp)

Food emulsions - Na caseinate (most widely used protein emulsifier due to stability in high pressure homogenisers) e.g. icecream, mayonaise…

Cheese analogue - Rennet casein

Chocolate - may be composed of SMP and whey powders

Bakery products -SMP and whole milk powder often used

36
Q

What is whey?

A

A by-product of manufacturing dairy products -particuarly cheese

37
Q

What are the different whey proteins?

A

Beta-lactoglobulin
Alpha-lactalbumin
Caseinomacropepties
Immunoglobins
Serum albumins
Lactoferrin and Lactoperoxidase

38
Q

______________ make about half the whey protein in milk.

A

Beta-lactoglobulin (type of whey protein)

39
Q

Alpha-lactalbumin (type of whey protein) forms part of the ________ ________ enzyme.

A

Lactose synthase

40
Q

Lactoferrin and Lactoperoxidase are __________.

A

actibacterials

41
Q

What are the functional properties of whey protiens?

A

Solublizers (sports drink), gelation, foaming
(aerated food) and emulsification

42
Q

What are the nutritional uses of whey?

A

Instant formulatioms - hydrolysis breakdown of allergenic proteins

Sports nutrition - protein

Nutrition Semester 1 (11 decks)

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