Grains Flashcards
Why do we need to measure the quality of grains?
Rice: Because different consumers require different types.
Wheat because it is used in so many food products.
Gelatinisation temperature
Temperature in cooking in which starch crystals begin to break down and allow water into the grain. non-reversible process. Key property of Amylopectin in Grain.
What are the main quality features for rice?
Determined mostly by starch
Amylose affects the stickiness and firmness of the cooked grain.
Amylopectin structure affects the gelatinisation temperature
What are the main quality features for wheat?
Protein content
Which feature of amylose leads to the increased intensity of blue and why?
Bonding with Iodine.
The greater the length of amylose chain helix leads to a greater intensity of blue.
Amylose is a chain of glucose molecules linked by alpha 1-4 bonds.
What part of the Differential Scanning Calorimeter (DSC) endotherm gives the value of GT and why?
The apex of the curve is the measure of gelatinisation Temperature- cooking can happen after the starch unravels- after the apex.
Area under the curve is the energy required to melt the starch.
When starch is cooled, what are the two processes that occur and what does this tell us in terms of the macromolecules?
Aggregation and Retrogradation (realign to form firmer texture- hardening of the gel).
Syneresis- excluding water
What are the direct features of the RVA curve? What are the derived ones? What do these tell us about the grain?
Pasting temperature
Peak viscosity- tell us the highest viscosity during heating- balance between swelling and rigidity assos. final product quality
Trough viscosity- measuring of weakening and disruption of granules due to heating and shearing.
Final Viscosity- ability to form viscous past or gel after cooking and cooling– product texture.
Which are the major grains
Rice, wheat, Maize and Barley –> get diverse range of products
Minor grains
oats, Buckwheat, sorghum, rye, spelt, quinoa, teff
What is the most important thing for wheat products
protein content. breads, pasta, cakes and biscuits have all different protein content
End us of Barley
Beer- barley grains are germinated in the process of malting.
Starch structure differs on several organisational levels. what are the organisational levels of Starch?
- Amylose (long chain- no branches) and amylopectin (huge, short chains with lots of branching)- has crystaline lamella (short chains that all line up) and amorphous lamella (bits with nothing).
- Blocklets- amylose surrounds multiple amylopectins (bond together though the cystaline lamella)
- semi-crystalline rings formed by lined up blocklets
- Granules
- compound granules (oats and rice)
How can starch structure be varied
- sizes of granules
- dif ratios of A and B granules in wheat, barley, rye
- different number of compound granules (oats and rice)
- deeper levels of structure
What are starch molecules made up of
chains of glucose molecules. 6 C.
Alpha 1-4 glucose linkages lead to
straight chains
Alpha 1-4 glucose linkages lead to
branchpoints
Amylose structure bonds max MW effect on structure
long straight chain
alpha 1-4 linkages
10^5
hardness, stickiness and retrogradation
Are amylose chains necessary to the formation of a starch granule.
No
amylopectin is essential.
Amylopectin
highly branched molecule
alpha 1-4 and alpha 1-6 bonds
10^8 9much bigger then amylose)
responsible for Tg, GT and swelling
What is the result of a mixture of long and short amylopectin chains in a distribution
Results in increased weakness
decreased strength
Decreases temperature to melt
cook at lower temperatures.
Glass Transition, Tg
first stage of melting.
reversible
used to make crunchy and crispy foods
Glass Transition, Tg
first stage of melting.
reversible
used to make crunchy and crispy foods
function of chain lengths
which is reversible Tg or GT
Tg
why is Tg reversible
because it involves the melting of starch- which can then reset. Recrystallises.
Gelatinisation Temperature, GT
Second stage of melting
irreversible
indicates cooking time
what will cause a lower cooking time. long or short chain lengths
A distribution of long and short (the greater short) will result in weaker clusters-> shorter cooking time.
what causes different chain lengths
Different enzymes.
a lack of starch synthaseIIa would result in less enzymatic activity–> shorter chains
function of Starch syntheses
Make chains longer. Each synthase makes a certain chain length
Function of starch branching enzymes
create branches by moving a part of the chain and reattaching it somewhere else
function of debranching enzymes
Trims
What does a mutation in SSIIa (rice) result in
more short chains in cluster –> softer texture and lower GT
shorter cooking time
What does a mutation in SSIIa (rice) result in (natural modification)
more short chains in cluster –> softer texture and lower GT
shorter cooking time
Result of silencing SSIIa in wheat (done by genetic modification)
Loss of short and second set of long
low GT and poor bread qualities
The natural mutation to BEIIb in rice and wheat results in
Leads to loss of long chains, much less diverse CLD. high GT (long cook time- unfavourable) , cooks very very hard, no swelling high RS, low GI -- taste terrible.
Three ways to change the properties of starch
- chemical modification
2. genetic modification 3. change to the physical properties
Chemical modification techniques examples
lots of different
- Acid modification- acid cuts the starch molecules into smaller size –> less viscosity, wet starch upon leaving to be cooled, opaque gel shall be obtained.
- distarch phosphate by POCL3- creates bond between starch molecules –> makes the gel tougher and more resistant to heat and shear.
What, in the gut of humans, digests starch
salivary amylase
Why can we only digest starch and not other CHO like cellulose, callose, etc?
Starch is made up of alpha 1-4 and alpha 1-6 bonds which can be digested by salivary amylase. The other CHO are beta bonded and we lack the enzyme required to break the beta bonds.
What are proteins
made up from 20 Amino acids
made up of an amino acid a carboxyl group and an R group (characterises the AA)
Draw a protein
amino group–alpha C (– R group)– carboxyl group
Levels of structure of a protein
primary structure- sequence of a chain of amino acids
secondary structure- hydrogen bonding of the prptide backbone causes the AA to fold into a repeating pattern
tertiary structure- 3 dimensional folding pattern due to side chain interactions
quaternary- protein consisting of more then one amino acid chain
What are the 9 essential AA
His, ILe, Leu, Lys, Met, Phe, Thr, Trp, Val.
what determines the ‘quality of the protein’
the amino acids in the protein
What are good sources of Histidine
Soy protein, eggs, parmesan, sesame, peanuts
What are good sources of Isoleucine
Eggs, soy protein and tofu, whitefish, pork and parmesan
Leucine
eggs, soy protein, whitefish, parmesan, sesame
What are good sources of Lysine
Eggs, Soy proteins, whitefish, parmesan and smelts
What are good sources of Methionine
Eggs, whitefish, sesame, mustard seeds, peanuts
What are good sources of Cysteine
Eggs, soy proteins, sesame, mustard seeds, peanuts
What are good sources of Phenylalanine
Eggs, Soy proteins, peanuts, sesame and whitefish
What are good sources of Tyrosine
Soy proteins, eggs, parmesan, peanuts, sesame
What are good sources of Tryptophan
soy protein, sesame, eggs, winged beans, chia seeds
What are good sources of valine
eggs, soy protein, parmesan, sesame and beef
What are good sources of valine
eggs, soy protein, parmesan, sesame and beef
proteins in a storage grain are called
storage proteins
AA in cereal proteins are generally low in
lysine
What are the four classes of storage proteins in cereal grains
- Albumins
- Globulins
- Prolamin
- Glutelins
These classes in all cereal grains, but go under differnt names
Lysine content is highest in the grain?
Rye
high levels of albumins and globulins
(prolamins= secalins)
Main proteins in Barley
prolamins and gluteins
fermantable sugars are higher with low protein
Which is the highest protein cereal
Oats
most nutritionally balanced
main protein in wheat
Gluten (glutenin +gliadin (prolamin))
How is gluten formed
when two classes of water-insoluble proteins in wheat flour (glutenin and gliadin ) are hydrated with water and mixed (kneading)
only dough can contain gluten
How is gluten formed
when two classes of water-insoluble proteins in wheat flour (glutenin and gliadin ) are hydrated with water and mixed (kneading)
only dough can contain gluten
What properties does gluten give bread
its viscoelastic properties by forming a network
what is the major storage protein of the rice grain
Glutelin (oryzenin)
what is the importance of proteins in rice
they stop it from breaking. broken rice is not good- strach falls out the broken end and forms a glue over the cooked rice.
what colour is a rice high in protein
yellow
Retrogradation
The hardening of rice after it has been cooked then put in the fridge. Proteins help strengthen the network that forms on cooking and cooling.
where are storage proteins found in grains
in the endosperm.
What is the definition of whole grain? Think of two examples of different whole grain foods
Whole grain foods still have the bran layer surrounding the white endosperm.
In terms of resistant starch or dietary fibre, what is the nutritional problem with the definition of whole grain?
Whole grain doesn’t lead to fermentation in the gut- therefore don’t get the benefits. (bran is detached from the grain)
What is the benefit of fermenting starch in our large intestine?
produces short chain fatty acids, like butyrate that does a lot of good. (e.g. decreased AP, altered gut microbiota)
How many types of resistant starch are there?
There are 5 types.
What other carbohydrates do we eat that we need to ferment? Why do we need to ferment them?
cellulose, arabinoxylans, beta glucans, and callose. They have beta bonds, so we can’t digest them.
What is the major problem with storing whole grain foods?
short shelf life due to the fatty acids oxidising into volatile compounds. The bran contains high levels of FA. volatile compounds can have an unpleasant aroma
What type of compounds lead to rancid aromas? What is the chemical source of those compounds?
Oxidation of fatty acids leads to aldehydes and ketones that are volatile and have unpleasant aromas.
