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Nutrition > Food Proteins > Flashcards

Food Proteins Flashcards

1
Q

What is a protein?

A

A long chain on amino acids

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2
Q

What are the functions of proteins?

A 
Biological processes
- Cell signalling 
- Cell adhesion 
- Immune response 
Structural functions
- Muscle and tissue composition 
- Cell walls
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3
Q

What is the primary structure of a protein?

A

The sequence of amino acids

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4
Q

What is the secondary structure of a protein?

A

Folding into alpha helices or beta pleated sheets

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5
Q

What is the tertiary structure of a protein and what types of proteins does it produce?

A

Secondary folding as a result of bonding between regions on the amino acid sequence

  • Linear proteins = structural functions
  • Globular proteins = transport functions
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6
Q

What is the quaternary structure of a protein?

A

Two or more polypeptides joining

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7
Q

What are the three classifications of proteins?

A 
Simple = just amino acids 
Conjugated = amino acids and a prosthetic group 
Derived = proteins modified by chemical or enzymatic treatment
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8
Q

Name 4 simple proteins.

A

Albumins
Globulins
Collagen
Gluten

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9
Q

Name 4 conjugated proteins.

A

Lipoproteins
Glycoproteins
Nuceloproteins
Phosphoproteins

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10
Q

Name 2 derived proteins and the way in which they are modified.

A

Soy proteins = chemical modification

Milk proteins = enzymatic modification

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11
Q

What are the 3 structural properties of proteins?

A

Formation of gels
Stabilising emulsions and foam
Film formation

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12
Q

How does gelation occur?

A

Association or cross-linking of protein chains
3D network formed
Water is trapped or immobilised which forms a rigid structure which is resistant to flow

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13
Q

Do globular proteins form thermally reversible or irreversible gels?

A

Thermally irreversible because proteins are denatured

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14
Q

Do fibrous proteins form thermally reversible or irreversible gels?

A

Thermally reversible

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15
Q

How are emulsions categorised?

A

According to they type of immiscible materials that form the continuous and dispersed phases

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16
Q

What type of emulsions do milk and egg proteins stabilise?

A

Oil in water

17
Q

Why are milk and egg proteins good emulsifiers?

A
  • They adsorb at interfaces and prevent aggregation
  • They are small enough to diffuse to the interface at a fast rate
  • They are large enough to increase energy of adsorption
18
Q

What compound are soya oil emulsions stabilised by?

A

Sodium caseinate

19
Q

When is adsorption at interfaces optimum?

A

The closer pH is to the emulsifiers isoelectric point

20
Q

How can emulsions be achieved if the protein layer is too thin to provide stabilisation?

A

By the forming of a thick bilayer between a protein and a polysaccharide

21
Q

What do proteins do once they are adsorbed at the interface?

A

Self-associate forming elastic networks

22
Q

What are edible films formed from?

A 
Gelatine 
Whey 
Soy 
Corn 
Wheat gluten
23
Q

What do films provide?

A

Barrier to moisture
Barrier to oxygen and carbon dioxide exchange
Biodegradable packaging

24
Q

What are enzymes?

A

Catalysts that speed up the rate of a reaction without being used

25
Q

What optimums do enzymes have?

A

Temperature
Time-temperature
pH

26
Q

How does pH have an affect on enzymes?

A

It changes the ionic state of amino acids which may affect the binding site

27
Q

Name five protein enzymes used in industry.

A 
Isomerase 
Invertase 
Lipoxygenase 
Proteases
Lactase
28
Q

What reaction does isomerase catalyse and how is it used in industry?

A

D-glucose to fructose

Fructose is much sweeter than glucose so can be used in sweetners

29
Q

What reaction does invertase catalyse and how is it used in industry?

A

Sucrose and water to a-D glucose and B-D-fructose

These sugars are produced for use in confectionery because they are more stable and will not crystallise

30
Q

What reaction does lipoxygenase catalyse and how is it used in industry?

A

Unsaturated fatty acids to fatty acid hydroperoxides
Prevents rancidity
Improves dough
Improves flavour of bread

31
Q

How are proteases used in industry?

A

Meat tenderization
Flavouring = umami
Cheese making

32
Q

How is lactase used in industry?

A

Added to some milk products for people who do not naturally have enzymes to break down lactose to glucose and galactose

33
Q

What protein chemical reactions occur in foods?

A

Reactions of carboxyl groups
Reactions of amine groups
Reactions of thiol groups
Reactions between amino acids

34
Q

Give an example of a protein chemical reaction that occurs in food involving the carboxyl group.

A

Decarboxylation of histidine to histamine

35
Q

Give three examples of protein chemical reactions that occur in foods involving the amine group.

A

Acetylation = increases solubility of protein isolates used in emulsions
Formation of nitrosamines = nitrites added in meat curing to give flavour, colour, prevent spoilage and protect against food borne pathogens
Maillard browning = reaction with the carbonyl group of sugars producing colour and flavour

36
Q

What are the disadvantages of protein chemical reactions?

A

Amino acids are modified making them unavailable

Toxic compounds such as carcinogens may be produced

37
Q

Give three examples of protein chemical reactions that occur in foods involving the thiol group.

A

Formation of disulphide bridges = increases dough extensibility and improves texture of meat batters
Discolouration in low acid, high protein canned products = reaction with tin or iron
Oxidation during freezing = oxidative rancidity

38
Q

Give an example of a protein chemical reaction that occurs in food between amino acids.

A

Cysteine and serine form dehydroalanine
Dehydroalanine and lysine form lysinoalanin
Lysinoalanine cannot be digested and is potentially toxic

39
Q

Name proteins which may be of interest to industry.

A 
Milk proteins 
Meat proteins 
Seafood proteins = source of essential amino acids but is not sustainable 
Legume proteins 
Oilseed proteins 
Cereal proteins 
Texturised veg proteins 
Algal proteins = blue/green seaweed has a high protein content 
Fungi proteins = used in quorn

Nutrition (27 decks)

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