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FOOD20003 > 3. Proteins > Flashcards

3. Proteins Flashcards

1
Q

What is the structure of an amino acid?

A
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2
Q

Why are proteins complex compared to polysaccharides?

A
  • Side groups on amino acids vary from one amino acid to the next
  • A protein is made up of about 20 different amino acids, each with a different side group
  • Polysaccharide is usually made up of the same repeating monosaccharide units or combo of a few different units
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3
Q

Which amino acids have carbon rich side chains making them HYDROPHOBIC?

A
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4
Q

Which amino acids are hydrophilic or polar and therefore interact well with water?

A
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5
Q

What pH’s do the charged amino acids interact at?

A
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6
Q

What is the primary structure of proteins?

A

The pimary structure of a protein is the linear sequence of amino acids as encoded by DNA

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7
Q

What are the two types of secondary structure that proteins have?

A

Alpha helices or beta sheets

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8
Q

How is the alpha helix stabilised?

A
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9
Q

How are beta sheets stabilised?

A

Beta sheets are formed when hydrogen bonds stabilize two or more adjacent strands

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10
Q

What is the tertiary structure of the protein?

A
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11
Q

Why are the charged amino acids important for structure in proteins such as ubiquitin?

A
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12
Q

How do membrane bound proteins make use of charged amino acids to inform their shape?

A
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13
Q

What are three factors the native structure of a protein depends on?

A
  1. Repulsive and attractive forces
  2. Interactions among the amino acid side groups of proteins
  3. The environment the protein is in.
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14
Q

Which levels of protein structure are disrupted when the protein is denatured?

A
  • Protein denaturation refers to changes in the secondary and tertiary structure of the protein, while the primary structure remains unchanged.
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15
Q

What are some of the forces that stabilise protein structure?

A
  • Hydrophobic interactions
  • Electrostatic interactions
    • Van der Waals interactions
    • Hydrogen bonds
    • Ionic interactions
  • COvalent bonds or chemical cross links
    • Disulfide bonds
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16
Q

What happens to a protein when it is denatured?

A
  • Undergo physical and chemical changes
  • Lose its biological activity
  • Lose solubility
  • Increase tendency to aggregate
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17
Q

What happens to an enzyme where it is denatured?

A
  • Loss of enzyme activity
  • Changes in reaction rate
  • Changes in affinity for its substrate
  • Changes to its optimum pH or temperature to funciton
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18
Q

In what ways is protein denaturation beneficial for food processing?

A
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19
Q

What are denaturants?

A

Factors that contribute to the changes in the environment surrounding the protein which result in disruption of interactions that stabilise the secondary and tertiary structure.

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20
Q

What are three physical denaturants?

A
  • Temperature induced
  • Sheer induced
  • High pressure induced
21
Q

What are the three chemical denaturants?

A
  • pH induced
  • Organic solvent induced
  • Salts and other additives
22
Q

How does temperature act as a denaturant?

A
  • Both high and low temp can cause proteins to denature, and the denaturation temperature of a protein is unique to the protein
  • Thermal stability of proteins is determined by the amino acid composition
  • Hydrophobic amino acid residues (Val, Ile, Leu, Phe) provide for higher stability than proteins with more hydrophilic amino acids
  • Some proteins also denature at cold temperatures, usually reverisble
23
Q

How can mechanical sheer acts as a denaturant?

A

Denaturant of food proteins can results from exposure to mechanical shear forces generate by processes such as shaking, whipping, mixing, sonicaiton, vortexing, flow through conduits, centrifugation, and texturisation.

24
Q

What are the sources of food proteins?

A
25
Q

What proteins are sourced from plants?

A

Gliadin, horedein, karifin, secalin, and zein are PROLINE and GLUTAMINE rich storage proteins found in wheat, barley, sorghum, rye and corn respectively

26
Q

How can plant proteins contribute to allergies?

A
  • These proteins are known to contribute to intolerance and allergenicity in certain individuals
  • the choice of the processing of food can amplify the allergenicity of some of these proteins
  • Eg. although dry roasting can impart flavour to peanuts, it can augument immunoreactivity and amplify the formation or unveiling of new allergenic epitopes in peanut proteins
27
Q

What broad categories of factors are there that influence funcitonal properties of proteins?

A
  • Intrinsic properties of protein
  • Extrinsic factors coming from the food system
28
Q

What are the intrinsic properties of food proteins that affect funcitonal properties?

A
29
Q

What are the external properties that influence the functional properties of proteins?

A
30
Q
A
31
Q
A
32
Q
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33
Q
A
34
Q

How does the characteristic of soy protein influence its use in bread?

A

Soybean proteins have neither gliadin nor glutenin, the unique proteins of wheat gluten. As a result, soy flour cannot be incorporated into bread without the use of special additives that improve loaf volume.

35
Q

How do we get from soybeans to soy products?

A
36
Q

What four groups of proteins does soybean contain?

A
  • Storage proteins
  • Enzymes and enzyme inhibitors ( >1% of the total protein) involved in metabolism
  • Structural proteins including both ribosomal and chromosomal
  • Membrane proteins
37
Q

What is soy protein isolate?

A
  • When you acidify defatted soybeal meal to pH 4.5-4.8 you prepare SPI and whey
  • SPI includes the mahor soybean isolation proteins
  • Classified into four categories 2S, 7S, 11S and 15S which sediment at different gravitational forced when solution is subjected to a centrifugation.
38
Q

What is the basic 7S globin structure from soybean?

A
39
Q

What is the basic 11S globulin structure from soybean?

A
40
Q

How does a protein gel form?

A
  • When partially unfolded proteins develop uncolied polypeptide segments that interact at specific points to form a 3D cross linked network
  • Partial unfolding with slight changes in secondary structure is required for gelation
  • heating, treatment with acids, alkali can contribute to partial unfolding of the native structure
41
Q

What interactions result in the formation of a protein gel?

A
  • 3D protein network forms because of protein-protein and protein-solvent (water interactions)
  • These interaction and gelation are accelerated at high protein concentrations because of more intense intermolecular contacts
  • Higher amound of cross linking provides fluidity, elasticity and flow behaviour of gels
42
Q
A
43
Q

How is tofu formed?

A
  • Tofu is a bean curd made by coagulating soymilk
  • Washed soybeans are ground with water. Then soymilk is obtained by filtration before or after heating
  • Ca induced and heat induced gelling mechanisms are used to form tofu. Salt coagulants are added while heating the soymilk to achieve this
44
Q

What is happening in this picture?

A
  • 7S and 11S proteins exist in the solution, and soy milk is made up of proteins and oil globule in the aqueous solution
  • Then salts are added, may decrease pH
  • The oil globules interact with the proteins and pH change partially denatures the protein exposing hydrophobic groups that interact with oil globules
  • Coagulation forms the network
45
Q

How can a good emulsion differ?

A
46
Q

What is an emulsion made up of?

A
47
Q

How do proteins prevent coalescence of foams and emulsions?

A
  • They have an amphipillic nature so they place themselves at the air-water and oil-water interface.
  • partial unfolding of the proteins enable it to interact with both oil and water
48
Q

How does the composition of soy protein affect its emulsification properties?

A
  • more 7S has better emulsifying properties than fraction with 11S
  • Better emulsifying properties of 7S globulins give higher rate of diffusion to the interface
  • Disulfide bonding in the 11S globulin may inhibit unfolding and decrease interactions at the oil/water interface
49
Q

how does the stability of emulsions prepared with mature or immature beans compare?

A
  • The stability of emulsions prepared with soy isolate from mature beans was higher than those from immature ones. This was due to the increased 7S fraction in the mature soybeans.
  • Preparing blends of soy proteins and caseins or whey protein diminished the undesirable off-flavor of soy protein.

FOOD20003 (14 decks)

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