7: Properties & Industrial Uses Of Proteins Flashcards
What are proteins?
Long chains of amino acids or chains of peptides (as these are short chains of amino acids)
How is the protein quality in food determined?
By the concentration of essential amino acids, (e.g. leucine, lysine, methionine, tryptophan)
How do proteins play a role in biological processes, and how do they have a structural or mechanical function?
Key role in biological processes:
- cell signalling
- cell adhesion
- immune response
Structural/mechanical function:
- muscle & connective tissue of animals
- cell wall of plants
How are proteins used on an industrial scale?
application in food, pharmaceuticals, medicine, cosmetics
e.g. enzymes widely used in the food industry
Describe and explain the structure of protein
- Primary : sequence of aa of the polypeptide chain
- Secondary : polypeptide folds as a result of H bonding between local aa. Alpha helices & B pleated sheets
- Tertiary : secondary folding as a result of bonding between peptides or polypeptide regions
Forming linear proteins with structural/mechanical functions (e.g. collagen in tendons, cartilage & bone) & globular proteins involved in transport & dynamic functions (soluble in aqueous environments: hydrophobic aa inside & hydrophilic in the periphery) - Quaternary structure : 2 or more polypeptides (haemoglobin)
What is a simple protein? Give examples
Give examples of fibrous (linear) and globular proteins
A simple protein (e.g. albumins, globulins, histones) is one that contains only amino acids (whereas conjugated contains a non-proteinaceous prosthetic group as well as amino acids)
- Fibrous proteins : collagen, keratin, elastin
Globular proteins : serum globulins, insulin etc.
What are the structural properties of proteins in industry?
- Formation of gels : gelation
- Stabilise emulsions & foams
- Form films
Why are proteins denatured when used in industry?
To boost their functionality (enhanced stability for emulsions/foams; enhanced gel formation; loss of solubility and activity)
What is gel formation?
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 resistant to flow
e.g. fibrous proteins are able to form thermally reversible gels : gelatine from collagen
How are proteins used to stabilise emulsions and foams?
e.g. proteins from milk and eggs are commonly used to stabilise oil in water emulsions & foams.
They adsorb at the oil-water and air-water interfaces, preventing aggregation (hydrophobic groups in contact with oil; hydrophilic groups in contact with water)
So that a droplet of oil can be within water without separating
How are proteins used in film formation?
e.g. gelatine, whey, soy, corn & wheat gluten proteins can be used to form edible films (coatings when applied to fruit & veg)
- act as a barrier to moisture & co2
- biodegradable packaging
Give examples of enzymes used in food industry
Hydrolases, for example : amylases; invertase (for sucrose hydrolysis, production of invert sugar syrup); lactase (for lactose hydrolysis).
What are proteases commonly used for in the food industry?
Meat tenderisation
e.g. papain from papaya
Bromelain from pineapple
Give examples of protein chemical reactions in food
- Reactions of the carboxyl group (decarboxylation of histidine into histamine = removal of carboxyl group, attach on an amino group instead -> can produce a severe allergic reaction e.g tuna)
- Reactions of the amino group :
Acetylation (attaching chain of carbohydrates = increased solubility)
Formation of nitrosaminides (when nitrites are added in meat curing)
Maillard browning (reaction between amino acids & sugars e.g. when toasting bread)
Explain the difference between whole grain vs ‘white’ grain wheat
Whole grain contains bran, endosperm & germ; whereas white only contains endosperm
Describe the structure of wheat (whole grain)
Brain = fibre rich outer layer that protects the seed & contains B vitamins & trace minerals
Endosperm = middle layer containing carbs & proteins
Germ = small nutrient rich core containing antioxidants, including vitamin E & B and healthy fats
What is the definition of gluten?
A protein complex derived from cereals such as wheat, rye, barley & oat
What is vital wheat gluten?
Gluten sold as a dried state (powder to be rehydrated)
Is produced from wheat flour by wet separation and controlled drying processes
How is gluten extracted from flour?
- Flour is mixed with water to form a dough
- Dough is allowed to rest and fully hydrated to produce gluten protein agglomerates
- Agglomerates are separated from starch by centrifugation in decanters
- Final stages : drying, grinding and sieving to obtain vital wheat gluten in powder form
Explain the different types of gluten (wheat) proteins
- Non gluten proteins (15%) : washed away with starch during processing (e.g. albumins & globulins)
- Gluten proteins (85%) : Glutenins & Gliadins
Glutenins = linear, higher molecular weight, help with elasticity
Gliadins = lower molecular weight, help with extensibility, act as bridges
Describe glutens structure
Glutenins and gliadins are associated through disulfide bonds, non-covalent H bonds & hydrophobic interactions
- Together they provide gluten with unique physical properties : viscosity & extensibility by gliadin; elasticity by glutenin
Describe the functional and sensory properties of gluten
- Insolubility and water holding capacity (improves product yield, softness & shelf life)
- Viscoelasticity (protein molecules form a cohesive, elastic matrix that can stretch and expand but maintain strength = elasticity allows for gas retention and controlled expansion e.g. for texture of bread)
- Flavour (bland/fairly neutral so wide acceptance in a range of products)
- Thermosetting (permanent hardening provides structural rigidity and bite characteristics)
How can gluten be modified to increase water solubility for emulsification and foam stabilisation?
- Deamidation with either acid or alkali treatment (changes structure slightly without denaturing protein to make it easier to digest & more bioavailable) e.g. used in milk & meat replacements
- Enzymatic hydrolysis of peptide bonds : beneficial effects on dough properties as peptides can form covalent & non covalent bonds
MODIFICATION BY PHYSICAL TREATMENTS:
1. Texturisation by extrusion : produce a fibrous structure to simulate meat fibres
2. High pressure
