BMS1064: Wk7 - Proteins Flashcards
What is the primary structure of proteins?
How are peptides different to proteins?
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
Describe the secondary structure of proteins.
Polypeptide folds as a result of hydrogen bonding between local amino acids.
Describe the tertiary structure of proteins.
What are the different types?
Further folding of secondary structure as result of bonding between peptides/polypeptide regions.
LINEAR/FIBROUS:
- 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).
Describe the quaternary structure of proteins.
Two or more polypeptides bound together. (e.g. haemoglobin)
What is the isoelectric point of a protein?
The pH at which their net charge is zero.
What are the 3 classifications of proteins?
Simple proteins = AAs only
Conjugated proteins = AAs + prosthetic group
Derived proteins = modified by chemical or enzymatic treatment
What are the structural properties of proteins in food science?
In what 3 thigns can they be used in food science?
- Formation of gels (gelation)
- Stabalise emulsions and foams
- Form films
What are the effects of denaturing proteins (for food)?
Loss of solubility and activity
Changes in functional properties
- enhanced gel formation
- enhanced stability for emulsions
- elastic films
What is gelation / gel formation?
The association or cross linking of protein chains to form a 3D network that traps or immobilises the water within it to form a rigid structure.
Looking at globular and fibrous protiens, is gelation reversible or irreversible?
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).
What are emulsions?
A mixture of two liquids that normally don’t mix (e.g. oil and water).
_______ from milk and eggs are commonly used to stabalise oil-in-water emulsions and foams.
How do they do this?
Proteins
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.
What affects interfacial activity?
- Molecular size
- Conformation (structure)
- Amino acid composition
- pH and solvent composition
What are the benefits of using proteins to form edible films on food?
What are examples of some proteins that can form films?
- 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
Name 5 enzymes used in food processing.
Invertase
Isomerase
Lipoxygenase
Protease
Lactase
What does the enzyme Isomerase do in food science?
Why is this beneficial?
Converts glucose to fructose.
Fructose from corn is sweeter than glucose.
Corn syrups = mixture of fructose and glucose.
What does the enzyme invertase do?
Why is this beneficial in food science?
Converts [sucrose] –> [glucose and fructose].
Reduces sugars for confectionary as they are more stable and less likely to crystalise.
What does the enzyme lipoxygenase do?
What are the desriable and undesirable results of it being used in food science?
Converts Unsaturated FAs -> FA hydroperoxides.
Improves dough and flavour of bread. (desirable)
Causes fat rancidty (undesirable)
How are proteases used in food science?
Meat tenderization.
Cheese making.
Flavouring
How is lactase used in food science?
To convert lactose -> galactose and glucose
Makes food more digestable for those who are lactose intolerant. (e.g. lactase added to milk)
What are the protein chemical reactions in food science? (4)
- Carboxyl group reactions
- Amino group reactions
- Thiol group reactions
- Other reactions between amino acids (e.g. discolouration in low acid, high protein products and oxidation during freezing)
How can carboxyl group reactions be used in food science?
To decarboxylate histadine into histamine.
(Histadine -> food poisoning, allergic reactions)
How can amino group reactions be used in food science?
Acetylation increases the solubility of proteins -> emulsions
Formation of nitrosamines (nitrates added in meat curing - flavour, colour, protection from bacteria)
Maillard browning - reaction with sugars giving desirable colour and flavour of bread, meats and coffee beans when toasted/cooked/roasted.
What are the cons of carboxyl and amino group reactions?
AAs are modified, becoming unavailable.
Production of toxic/carcinogenic compounds.
