Bitterness Flashcards
the color and the bitterness results from the ___ processing step of beer making
kilning
What are beer’s quality factors
1- colour 2-clarity 3-%alcohol 4-taste 5- foam
What is responsible for the darkening of malt?
Maillard reaction is responsible for the darkening
Darkness of malt increases with ____
kilning temperature
what is the cause of beer haziness
hte binding of proanthocyanidins to the barley proteins
Prodelphinidins have ___ substitution on the ___ ring
OH B ring
What is the barley strain “clarity”
a strain of barley proteins that do not bind proanthocyanidins (preventing beer haziness).
What was the problem of the GMO barley strain “clarity”
the barley’s was not resistant to fusarium
In which step of the beer processing are hops added ?
to the beer brewing step
The floral aroma from hops are due to ____ which are lost during heating
terpenes
What is the oktoberfest umlagerung
it is an isomerization
Which part of the hops gives the bitter acids
the glands (they also produce the aroma compounds (terpenoids))
T or F : hops contains alpha acids which are not bitter by themsleves
true, during the heating they will convert into iso-alpha-acid which are bitter
T or F : the iso-alpha acid and alpha acid have the same molecular weight
true because the oktoberfest umlagerung is a isomerization rection
What gives the bitter acids molecules its antimicrobial activity
the prenyl group attached
what is this molecule
iso-alpha acid
What is this molecule
T or F : bitterness of iso-alpha acids more intense than that of quinine
sulfate
true
Why are alpha acids considered even though they do not contain a COOH group
because of a keto-enol tautomerism and the hydrogen atom attached is loosely bound and has a pKa of 5.0
Why do we say that there is a low efficiency at making bitterness in beers
only up to 30% conversion into iso-alpha-acids
What are the three strategies employed to improve the efficiency of hops at creating bitterness in beers
- using CO2 extracted bitter compounds from hops
- using modified iso-alpha acids
- Using hop pellets
What is the labelled line model?
that one TRC is responsible for detecting one taste only and it is bound to a nerve fiber that only brings the message of this taste modality
T or F : we know all the ligands for all the bitter receptors
False, many have not been deorphanized yet. orphan receptor is a receptor that we don’t know what is the ligand for its opening. So deorphanise means to find the ligand.
Which receptor family is responsible for the taste of bitter compounds
T2R also reffered to as TAS2R
T2Rs belong to the ____ which is a ____ receptor
G-protein-coupled receptors (GPCRs) which is a transmembrane receptor
T or F : all bitter compounds are recognized by the T2R receptors
False, T2R is a family with 25 members and each member recognizes a distinct set of molecules, although overlap in specificity has been reported
the slightly different T2R proteins are called ____ which are created because of ___
haplotype SNP (single nucleotide polymorphism)
T or F : one SNP leads automatically for a haplotype receptor
false because the nucleotide changed could givea different codon that still gives the same a.a
What underlie the inter-individual variation in bitter receptors
the haplotypes
When the bitter ligand links the receptor by ___ the receptor changes conformation and cleaves the ___ of the ____ and they act as messengers
key lock recognition
alpha subunit from the beta-gamma subunit
How can the taste induction can be studied
with recombinant mammlian or yest cells engineered to express the T2R and a fluorescent dye that binds calcium
What is the difference between alpha and beta acids
beta acids have an extra prenyl group
betsa acids are more hydrophobic because of this extra prenyl group replacing the OH and lapha acids are more water soluble
alpha acids have ___ prenyl groups while beta acids have ___
alpha : 2
beta : 3
____ are more water soluble than ___
alpha acids
beta acids
Humulones are ____ acids
alpha
Lupulones are ___ acids
beta
T or F : the iso-alpha and iso-beta acids have different stereoisomers
true there is the cis and trans configurations
in the cell-based assay which cells release more calcium (produces a stronger response)
the alpha and beta acids release more than the iso alpha and iso beta acids
T or F : all the bitter acids of beer activate the T2R
true
Co-humulone can activate two T2R and this is called ___
Functional redundancy
what is a mock trasfer
when you insert a gene of a receptor that is not activated by the bitter compound in your yeast HEK cell to do a control
when can’t you use the EC50 in the cell based assay?
When the bitter compound is toxic to cells or when the bitter compound is insolbule
T or F : the alpha bitter acids produces a stronger response in the cell based assay than in the sensory panels.
true
What explains the differences between cell based assay and senosry pannel for the bitterness of alpha/beta and iso-alpha/beta acids
the interaction with the oral mucosa can’t be predicted by the cell-based assay and beta acids are more hydrophobic than alpha acids and so they will bind the mucosa and will be less available for the receptors
T or F : the iso alpha/beta acids are not bound to the oral mucosa and so their intensity in sensory pannels is stronger than alpha/beta acids
ture
the alpha and beta acids are more___ (polar/apolar) than iso alpha and iso beta acids
apolar and so they will bind the oral mucosa reducing their availability at the receptor
What are the advantages of the cell-based assay?
- you can find out the receptor responsible for the taste of a particular compound
- you can see the intrinsic bitterness of a compound (without the other interactions in the mouth)
- cheaper in the long term
- not influenced by the tainning of the sensory pannelist
- less compounds needed because sensititivy is higher
- high throughput : many compounds can be tested rapidely
What are the disadvantages of the cell-based assay?
- you can’t predict the interaction in the mouth
- Can’t test the response of multiple T2r at the same time (synergic effect not accounted for)
- cross-modal interaction not accounted for (for example the taste of sweetness present masking a bit of the bitterness)
- can’t measure the inter-individual variation of tasting bitterness
- EC50 can be difficult to measure if it is detrimental to the cell viability
What explains the change in bitterness of beta acids upon heating
heating leads to the formation of tricyclo-beta acids because of the folding over of the prenyl group
which acids are sensitive to light ?
the alpha and iso alpha acids
T or f ; the trans/cis ratio is similar between companies
true it is stable around 0.40
why are beta acids less abundant in beers
beta-acids are less abundant in beer : because they are less abundant in hop and because of their poorer water-solubility
Why do some beer taste/smell like skunk ?
Removal of the prenyl group of iso alpha acids and reaction with sulfur containing compounds.
what are the conditions you need to have the formation of prenyl mercapan
UV light and sulfur containing compounds (as well as a iso-alpha acid)
What are the modification that can be done to iso-alpha acids to reduce their conversion in prenyl mercaptan
- Hydrogenation of the molecule (tetras)
- reduction (rhos)
- Combination of both (hexas)
whart is the protein responsible for the stability of beer foams
LTP1 : lipid transfer protein 1
LTP1 are rich in ___
cystein which make disulfide bridges and makes the protein very stable
How does LTP1 are modified by the processing of beer to make them more available to air-beer interphase
when they are heated, the apolar hydrophobic center are exposed because of the breaking of the disulfide bridges
T or F: Native barley LTP1 have poor foaming properties
true, the heating is what expose the hydrophobic core and the glycosylation due to maillard increase it amphilphalic properties
T or F : th e hops acids are also implicated in the foam stability
true but we do not know why
__ and ____ have higher foam-stabilizing potential than ___ and ____
Tetras’ and ‘hexas’
‘isos’ and ‘rhos’
why is modification of iso alpha acid not always a good thing
because the tetras an the hexas alpha acid gives a cling pattern because of the increased foam stability. This cling pattern can be perceived as a quality defect of beer.
What is gushing due to
fungal proteins from contaminated beer from fusarium
what is the protein responsible for the gushing effect
hydrophobins
