Food Proteins Flashcards
What is a protein?
A long chain on amino acids
What are the functions of proteins?
Biological processes - Cell signalling - Cell adhesion - Immune response Structural functions - Muscle and tissue composition - Cell walls
What is the primary structure of a protein?
The sequence of amino acids
What is the secondary structure of a protein?
Folding into alpha helices or beta pleated sheets
What is the tertiary structure of a protein and what types of proteins does it produce?
Secondary folding as a result of bonding between regions on the amino acid sequence
- Linear proteins = structural functions
- Globular proteins = transport functions
What is the quaternary structure of a protein?
Two or more polypeptides joining
What are the three classifications of proteins?
Simple = just amino acids Conjugated = amino acids and a prosthetic group Derived = proteins modified by chemical or enzymatic treatment
Name 4 simple proteins.
Albumins
Globulins
Collagen
Gluten
Name 4 conjugated proteins.
Lipoproteins
Glycoproteins
Nuceloproteins
Phosphoproteins
Name 2 derived proteins and the way in which they are modified.
Soy proteins = chemical modification
Milk proteins = enzymatic modification
What are the 3 structural properties of proteins?
Formation of gels
Stabilising emulsions and foam
Film formation
How does gelation occur?
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
Do globular proteins form thermally reversible or irreversible gels?
Thermally irreversible because proteins are denatured
Do fibrous proteins form thermally reversible or irreversible gels?
Thermally reversible
How are emulsions categorised?
According to they type of immiscible materials that form the continuous and dispersed phases
What type of emulsions do milk and egg proteins stabilise?
Oil in water
Why are milk and egg proteins good emulsifiers?
- 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
What compound are soya oil emulsions stabilised by?
Sodium caseinate
When is adsorption at interfaces optimum?
The closer pH is to the emulsifiers isoelectric point
How can emulsions be achieved if the protein layer is too thin to provide stabilisation?
By the forming of a thick bilayer between a protein and a polysaccharide
What do proteins do once they are adsorbed at the interface?
Self-associate forming elastic networks
What are edible films formed from?
Gelatine Whey Soy Corn Wheat gluten
What do films provide?
Barrier to moisture
Barrier to oxygen and carbon dioxide exchange
Biodegradable packaging
What are enzymes?
Catalysts that speed up the rate of a reaction without being used
What optimums do enzymes have?
Temperature
Time-temperature
pH
How does pH have an affect on enzymes?
It changes the ionic state of amino acids which may affect the binding site
Name five protein enzymes used in industry.
Isomerase Invertase Lipoxygenase Proteases Lactase
What reaction does isomerase catalyse and how is it used in industry?
D-glucose to fructose
Fructose is much sweeter than glucose so can be used in sweetners
What reaction does invertase catalyse and how is it used in industry?
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
What reaction does lipoxygenase catalyse and how is it used in industry?
Unsaturated fatty acids to fatty acid hydroperoxides
Prevents rancidity
Improves dough
Improves flavour of bread
How are proteases used in industry?
Meat tenderization
Flavouring = umami
Cheese making
How is lactase used in industry?
Added to some milk products for people who do not naturally have enzymes to break down lactose to glucose and galactose
What protein chemical reactions occur in foods?
Reactions of carboxyl groups
Reactions of amine groups
Reactions of thiol groups
Reactions between amino acids
Give an example of a protein chemical reaction that occurs in food involving the carboxyl group.
Decarboxylation of histidine to histamine
Give three examples of protein chemical reactions that occur in foods involving the amine group.
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
What are the disadvantages of protein chemical reactions?
Amino acids are modified making them unavailable
Toxic compounds such as carcinogens may be produced
Give three examples of protein chemical reactions that occur in foods involving the thiol group.
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
Give an example of a protein chemical reaction that occurs in food between amino acids.
Cysteine and serine form dehydroalanine
Dehydroalanine and lysine form lysinoalanin
Lysinoalanine cannot be digested and is potentially toxic
Name proteins which may be of interest to industry.
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
