Seed Storage Proteins Flashcards
Of wheat proteins, which are useful for bread?
Where are seed storage proteins found?
- Underneath bran layer
- Within the endosperm
Who is Thomas B. Osborne?
- He fractionated wheat kernels
What are Osborne fractions?
Successive extraction of wheat flour yielded:
- Soluble in water (albumins)
- Soluble in salt water (400 mM NaCl) (globulins)
- Soluble in 70% ethanol (eq) (prolamins)
- Insoluble (or soluble in other compounds like 60% 1-propanol) (Glutelins)
Further separation by electrophoresis, RP-HPLC.
Which Osborne fraction are each of these found in?
Successive extraction of wheat flour yielded:
- Soluble in water (albumins)
- Soluble in salt water (400 mM NaCl) (globulins)
- Soluble in 70% ethanol (eq) (prolamins)
- Insoluble (or soluble in other compounds like 60% 1-propanol) (Glutelins)
Why are Cheerios no longer labelled gluten-free?
- Made with oats
- Monitor to make sure oats are not contaminated with wheat, rye, barley
- Must contain less than 20 ppm (mg/kg) of ‘gluten’
Why are Osborne fraction historical names confusing?
Non-systematic naming for different fractions in different seeds.
What are gliadins?
- Wheat prolamins (some are sulfur rich some are sulfur poor)
- Very complex that are difficult to study that are not amenable to NMR or crystallography.
What are glutenins?
- Polymers in grain/flour
- Intermolecular disulfide bonds in grain/flour
What is a viscoelastic dough?
- Wheat flour + water + force
- Removal of starch (rinsing with water) leaves gluten
Only […] produces functional gluten.
Wheat
Rye dough properties > due to pentosans (CHO)
Rye dough properties > due to […]
pentosans (CHO)
Gluten =
90% protein (gliadins; glutenins); 8% lipid; 2% carbohydrate
Isolated in 1728, kneading dough in a stream (Jacopo Beccari)
It’s not gluten until you add water (removal of starch), and force, and it assembles into viscoelastic dough.
Describe the structure of gluten.
- Amorphous by SAXS
- Gliadins: remain monomeric; ‘lubricant’ for the large glutenin aggregates
- Glutenins: form large aggregates of millions of kDA; S-S intermolecular linking
What is the effect of ratio of gliadin to glutenin on gluten tensile strength?
- More gliadian = more pliability (less force required to stretch the dough a long way)
Gliadins (lubricant; monomeric); glutenin (large aggregates)
What are the drawbacks to using gluten in meat analogues?
- Low in essential amino acids (especially Lys, Met)
- Allergens; digestive issues
- Celiac disease
What are the health concerns with gluten?
- Note that not all of these issues are due to gluten alone (e.g., see the fructans)
Describe where legume proteins come from.
Describe worldwide production of soy proteins.
Describe the Osborne fractions of soy proteins and the proximate composition.
Describe the sedimentation behaviour of soy proteins.
- 11S are most common (glycinin, a legumin)
- 7S (beta-conglycinin, a vicilin)
Describe legume proteins.
Found in plants and bacteria. Not found in humans (but our microbiome produces them).
Vicilins (7S) and legumins (11S)
Describe the structure of soybean beta-conglycinin.
Visilin, 7S
- Hetero-trimer (α, α’, β); could be a mixture
- MW: 150-200 kDa
- No cysteines
- Forms softer gels
- Glycosylated: Glycoprotein (N-linked): Asn-X-Ser or Asn-X-Thr
- Where X is any amino acid except proline
Describe the structure of soybean glycinin.
- Hexamer at pH 7.6
- Trimer at pH 3.8
- MW: 300-800 kDa (hexamer)
- Forms firmer gels
- Hexamer:
- 18 Cys
- 6-SH
- 6 S-S
Legumin, 11S
Soybean glycinin forms a firmer gel than soybean beta-conglycinin.
True or False?
True.
Soybean glycinin forms a softer gel than soybean beta-conglycinin.
True or False?
False.
Soybean glycinin forms a firmer gel than soybean beta-conglycinin.
Soybean beta-conglycinin forms a firmer gel than soybean glycinin.
True or False?
False.
Soybean beta-conglycinin forms a softer gel than soybean glycinin.
Soybean beta-conglycinin forms a softer gel than soybean glycinin.
True or False?
True.
Legumin’s are cut into […]
- acidic + basic chains
- primary sequence is cut into these chains
- a disulfide bond joins them together
- can be separated by adding a redox reagent like DDT
- signal sequence is removed (may be ignored when looking at structure since it is not a component of the final structure)
What is similar/different about vicilins and legumins?
- Same topology
- Low sequency identity
What are anti-nutritional factors in seeds?
- Protease inhibitors (limits ability to absorb nutrients)
- Must cook to denature!!
There’s also agglutinin (a lectin)
What is agglutinin?
- A ‘lectin’ (protein that binds CHO with high affinity)
- e.g., glycoproteins on mucosal cells of small intestine can be bound by these anti-nutritional factors and block their function = nutrient malabsorption
Another lectin is ricin from castor bean = highly toxic!!
How can we inactivate these proteins but retain functionality of the 11S and 7S ‘good’ proteins?
What is phytic acid?
- Protein bodies (PB)
- Oil bodies (OB)
- Phytic acid, spherical structures (PA)
- Artefacts, white dots (A)
PA = binds minerals = anti-nutritional factor!!!
What is the process for legume protein exctraction?
- Dehull
- Hexane oil extraction
- Aqueous extraction ~pH 8 (e.g., use Na-bicarbonate)
- Soybase is used in tofu
What is the difference between soy protein concentrate and soy protein isolate?
- Concentrate: only soluble CHO removal
- Isolate: insoluble CHO and dietary fibre removed
Describe the process to make soy protein concentrate.
The method you choose can affect the functionality of the protein.
Describe the process to make soy protein isolate.
- Residue = insoluble fibre
- Solubilize protein to separate from insoluble fibre
Soy proteinate has better solubility characteristics.
When you run legume proteins on SDS page, how do the banding patterns appear?
- A reducing agent has been added, so the acidic and basic subunits of the 11S proteins run separately.
Describe considerations required for constructing a protein-based food.
- Predictability is hard
- So people just use trial and error to see how changing a protein somehow affects its functionality.
New technology: membrane technologies: ultrafiltration/diafiltration.
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Evaluate the impact of the extraction conditions to obtain SPI with low phytic acid content
- Protein modification: Fewer protein-divalent cation-phytic acid ternary complexes were formed making the phytic acid removal more efficient
- Functionality/applications: Improvement of solubility of SPI
New technology: Ultrasound
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Evaluate the rheological properties of the microstructure of gel-like emulsions from native and preheated SPI, under well-controlled conditions.
- Protein modification: Colloidal destabilization, especially droplet aggregation through strong attractive interactions between emulsion droplets.
- Functionality/applications: Improve the emulsification efficiency and thus can exhibit more potential to be applied to prepare the gel-like emulsions.
New technology: Acid treatment
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Obtain a food ingredient with foaming properties using acid treatment followed by neutralization.
- Protein modification: Proteins unfold, exposing hydrophobic patches and become more flexible; favours their adsorption in the interface and decreases the surface tension.
- Functionality/applications: Improved surface and foam properties
New technology: Acylation with saturated fatty acids
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Effects of acylation on the emulsifying properties of soy proteins using a variety of saturated fatty acids.
- Protein modification: Proteins unfolding and increase the dissociation of the subunits from the quaternary structures, as well as shifting the isoelectric point to lower values.
- Functionality/applications: Functional properties (emulsifying) of soy proteins were successfully improved.
New technology: Enzymatic hydrolysis
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Study the effects of combined extrusion pre-treatment and controlled enzymatic hydrolysis using pancreatin on the emulsifying properties of SPI
- Protein modification: Proteins have specificity to peptide bonds, cleaving them, exposing hidden hydrophobic residues and reducing molecular size.
- Functionality/applications: Produced prominent benefits in improving emulsifying capability of SPI and the stability of their emulsions.
New technology: Oxidation by peroxyl radicals
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Characterize the effects of acrolein on soy protein structure.
- Protein modification: Acrolein reacted with the imidazole group of histidine residues, the 3-amino groups of lysine residues, and the sulfhydryl groups of cysteine residues in soy protein to form covalent adducts, which contributed to protein carbonylation, degradation of protein sulfhydryl groups and cross-linking formation.
- Functionality/applications: Oxidation by peroxyl radicals affect protein structure; modifying SPI functional properties.
New technology: High hydrostatic pressure
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Investigate the effects of HP treatment on the aggregation and structural conformation of the proteins in SPI.
- Protein modification: The treatment led to different changes in protein solubility, surface hydrophobicity, free SH content, and secondary structure and unfolding. The unfolded proteins tend to aggregate mainly via hydrophobic interactions.
- Functionality/applications: Improvement of emulsifying activities due to the formation of protein aggregates including those insoluble and soluble.
New technology: Phosphorylation
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Evaluate the degrees of phosphorylation and the best conditions of phosphorylation of SPI
- Protein modification: Phosphorylation made the repulsion stronger than gravitation and the exposure of hydrophobic groups in the phosphorylated SPI favoured the diffusion and the measurement of protein in the oil-water interface.
- Functionality/applications: Change in functional properties such as emulsification, solubility, viscosity.
New technology: Transglutaminase and Maillard cross-linking
State:
* Objective
* Protein modification
* Functionality/applications
- Objective: Evaluate the effects of TGase pre-incubation and ribose-induced Maillard cross-linking in the SPI behaviour.
- Protein modification: Catalyzing an acyltransfer reaction between gamma-carboxyamide group of peptide bound glutamine residues (acyl donors) and variety of primary amines (acyl receptors), including the e-amino group of lysine residues to form an epsilon-(gamma-glutamyl) lysine isopeptide bond and reducing sugars and amino groups of amino acids and proteins to proteins cross-linked protein in Maillard reaction.
- Functionality/applications: Obtain higher G’ values in combined cross-linked samples.
G’ (the storage modulus) is a measure of the elasticity or solid-like be
G’ (the storage modulus) is a measure of the elasticity or solid-like behavior of the soy protein isolate (SPI) gel or network. It reflects the ability of the protein matrix to store and recover mechanical energy when subjected to deformation.
Higher G’ values mean that the protein network is more structured, elastic, and resistant to deformation, indicating stronger gel formation. It reflects the ability of the protein matrix to store and recover mechanical energy when subjected to deformation.
Describe tofu production.
- Soy protein in milk/extract
- BOIL to unfold proteins
- Unfolded proteins
- ADD CALCIUM (multivalent cation) to cross-link proteins
- Network of protein clumps = tofu
Tofu is a protein gel.
Tofu used for ~2000 years (Han dynasty, China)
Describe extrusion.
High moisture cooking
Extrusion is a more mature technology than shear cells, which are a bit niche. Also extrusion can be more continuous whereas the shear cell is batch-based process.
