GRAINS Flashcards
What are the 4 major grains?
- Rice
- Wheat
- Maize
- Barley
What are some examples of minor grains?
- Oats
- Buckwheat
- Sorghum
- Rye
- Quinoa
What is the white part of the grain called?
Endosperm
What is the outer layer of the grain called?
Bran
What are the two types of starch contained in starch granules?
Amylose and Amylopectin
Describe the structure of amylose?
Long chains of glucose molecules
Describe the structure of amylopectin
Short branched chains of glucose molecules
What are the two types of lamella in amylopectin?
Crystalline lamella: the short chains of glucose which are the branches and crystals
Amorphous lamella: the longer glucose chains which extend down into the next layer
How does amylopectin arrange itself?
In ‘blocklets’ which then arrange in semi-crystalline rings
What are the two types of starch granules in wheat?
- A granules: big
- B granules: small
ratio of these two impacts functionality as they absorb water differently
What bond constitutes straight bonds?
alpha 1-4 glycosidic bonds
What bonds cause bends in linkages?
alpha 1-6 glycosidic bonds
How long are amylose molecules?
200-10,000 glucoses long
What is the approximate molecular weight of amylose?
10^5
Which starch is NOT necessary for the formation of starch granules?
Amylose
How long are amylopectin chains/branches?
6-25 glucoses
What is the approximate molecular weight of amylopectin?
10^8
What properties is amylose responsible for?
- Hardness
- Stickiness
- Retrogradation
What properties is amylopectin responsible for?
- Glass transition
- Gelatinisation temp
- Swelling
Describe the role of amylose in rice?
Amylose is the most important trait of rice quality
Ranges from 0-30%
Content determines sensory trait:
- high amylose = less sticky
- low amylose = more sticky
Explain the relationship between amylopectin chain length and functional properties
Shorter chains make the crystal weaker
Long chains make the crystal stronger
Uniform long chains makes for the strongest crystal
What is Gelatinisation Temperature (GT)?
When cooking the starch it is the point at which the crystals across the top melt and water can enter the granules start swelling. It is irreversible
Occurs at lower temps in grains with weaker crystals
Occurs at higher temps in grains with stronger crystals
What is Glass Transition?
The first cooking process to occur, which is reversible.
It is a relationship between moisture and heat. Polymer melts but when heat is taken away it rehardens
What enzymes makes amylose?
Granule Bound Starch Synthase (GBSS)
What does Starch Synthase 1 (SSI) do?
Makes the chains up to 6 glucose units
What does SSII do?
Takes the 6 glucose units up to 25 units
What do SSIV and SSV do?
Synthesise the long chains that transverse multiple layers
What do starch branching enzymes do?
Create alpha 1-6 linkages
What do starch debranching enzymes do?
Trim the ends of the lamella to try and create even lengths
What occurs when SSIIa is missing?
It is hard to make chains longer than 6 glucose molecules and so they remain at 6 molecules long
What occurs when there is a SSIIa mutation in rice?
The molecules will be at a max length of 6, so there will be more short chains in clusters
This causes a softer texture and lower gelatinisation temp
What occurs when BEIIb is not active in rice?
There becomes huge variation in the chain length and changes the structure at a molecular level
It gives the rice a very high GT, is very hard once cooked and does not swell. It has high resistant starch and low GI
What happens to starch after acid modifying?
- Becomes less viscous when cooked
- forms opaque gel when cooked
What happens to starch when it is cross linked?
- makes a hard tough gel
- more resistant to heat and sheer
What are 3 quality traits of rice?
- Length & width
- Chalk
- Texture
Give an example of a rice which has a high amylose content?
Basmati rice (hard and seperate grains)
Give an example of a rice which has a low amylose content
Sushi rice (sticky)
What is used to test the amylose content and how does this work? What about amylopectin
Iodine (blue) is used to test amylose, it lodges itself in the helix structure of the amylose.
Darker blue reaction = longer helix
Light blue reaction = short helix
Amylopectin and iodine for a red coloured reaction
How is gelatinisation temperature measured?
Using a differential scanning calorimeter (DSC)
What is the relationship between GT and texture
If the GT is `60C that is ideal
The lower the GT the slower the grain takes to cook and the nicer the texture
Grains which have a high GT cook very fast when they hit that temp and then the structure falls apart
What is RVA and what are the 3 things that it directly measures?
RVA = Rapid Visco Analysis
Directly measures:
- Peak Viscosity: how much is swells
- Trough Viscosity: how much the gel breaks down during sheer
- Final Viscosity: how much retrodegration occurs
What is ‘setback’ and what does it mean?
The final viscosity - peak viscosity
If the setback is positive there is a high amylose content
What is ‘breakdown’ and what does it mean?
Peak viscosity - trough viscosity
Breakdown gives us an indication of how much sheer occurs
Which EAA is low in plants?
Lysine
What are proteins called in cereal grains?
Storage proteins
What are the 4 classes of storage proteins found in all grains?
- Albumins
- Globulins
- Prolamins
- Glutelins
Which storage protein is water soluble?
Albumins
Which storage protein is salt soluble?
Globulins
Which storage protein is alcohol soluble?
Prolamins
Which storage protein is alkali soluble?
Glutelins
What is the name of prolamin in Maize?
Zein
What is the name of prolamin in Rye?
Secalins
What is Triticale and what is it used for?
a cross of wheat x rye
Predominantly used for grain feed for animals
What is the name of prolamin in triticale?
Triticalins
What is the name of prolamins in Barley?
Hordeins
Do brewers prefer high or low protein content in barley?
Low
What is the name of prolamins in Sorghums?
Kafirins
What is the name of prolamins in Oats?
Avenins
What is the name of globulins in Oats?
Avenalins
What is the most common protein in rice and what is it called
Glutelins are the most common protein
Known as oryzenin in rice
What is the relationship between protein and amylose content in rice?
High protein = low amylose
What is the name of prolamins in Wheat?
Gliadins
What is the name of glutelins in Wheat?
Glutenins
What sort of proteins in wheat are essential for good bread?
High molecular weight glutenins are high in sulfur which is essential for good bread
What two proteins does Gluten consist of?
Gliadin + Glutenin
prolamin)+(glutenlin
What are the 3 types of monomeric gliadins?
- Alpha/Beta
- Gamma
- Omega
The Glutenin genes
Wheat is hexaploid which means it has 3 sets of paired chromosomes: A, B, D
What are both glutenin and gliadin responsible for in gluten?
Glutenin = elasticity
Gliadin = viscosity
What type of grain is pasta made from? Explain how gluten works in pasta
Fresh pasta is made from durum semolina (which is tetraploid)
During extrusion (drying) a protein networks covers the starch which causes a type of resistant start
What effect does protein content have on rice?
High protein content is detrimental to translucence
Higher protein content is linked to yellower grain
Explain how different growing conditions effect the protein synthesis in rice
In high nitrogen growing conditions, protein synthesis is the strongest sink for carbon ( from glucose)
So in high nitrogen conditions we get low amylose content
Explain the effect protein has on the swelling of rice during cooking
When water is added during cooking, the proteins grab water at a lower temperature than starch, so therefore there is less water for the starch to consume, so the grain swells less
What effect does protein have on retrodegration in rice?
High protein rice has higher levels of retrodegration
Explain what happens to basmati rice when stored?
When stored for longer than 9 months, oxidation and disulphide bonds form
Peak viscosity decreases with storage (due to disulphide bonds)
Explain the difference in mineral content between whole grains and white grains
The bran is a pericap, which is green (meaning it can photosynthesise/ transpire). These processes bring about water flow through the xylem which contains minerals
Explain why whole grains have a shorter shelf life than white grains
The bran contains lots of lipids and lipoxygenase enzymes which easily oxidise lipids into fatty acids
The double bonds in fatty acids are very susceptible to oxidation, making them go rancid
What is Resistant Starch 1?
RS1: physically unable to be digested in the small intestine due to a capsule (e.g. bran) so the grain moves to the large intestine
What is Resistant Starch 2?
RS2: Uncooked starch granules, found in any uncooked flours and green bananas
What is Resistant Starch 3?
RS3: Retrodegraded starch. When the starch is cooked and then cooled, it makes it difficult for the enzymes to attack
What is Resistant Starch 4?
RS4: Chemically modified starch. Linked starch molecules are difficult to be digested
What is Resistant Starch 5?
RS5: Lipid amylose complexes. When a lipid lodges itself within an amylose helix it makes it difficult to digest
What are the 3 main groups of microbiota in the gut?
- Bacteroids
- Preveotella
- Ruminococcus
Which variety of microbiota is associated with high fibre diets?
Prevotella
high butyrate producers
Which variety of microbiota is associated with high proteins/ animal fat diets
Bacteroids
How is protein quality determined in pulses?
The ratio of albumin:globulin and the ratio of the two major globulins, 11S:7S
What is a major functioning property of albumin in pulses?
Foaming (chickpea albumin can be whipped like egg white)
What types of resistant starch do pulses contain?
RS1 and RS3
What is raffinose comprised of?
Sucrose + galactose (alpha 1-6 bonds)
What are the 3 types of raffinose?
- Sachyose
- Verbassose
- Raffinose
Why are sachyose and verbassose unable to be broken down in the small intestine?
They are both bonded by alpha 1-6 gal bonds.
These can only be broken down by the α 1-6 GAL enzymes, which humans do not have, which means they pass through into the large intestine where they are fermented
The fermentation of raffinose produces methane, hydrogen and CO2 which causes pain in the gut
