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Food chemistry summary Molecular Gastronomy (FPH20806)
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Complete summary of all the relevant topics of food chemistry explained during this course (Colour changes and food flavours)
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TASTE SENSATIONSFive basic tastes
1. Sweet
2. Salt
3. Sour
4. Bitter
5. Umami
CHEMICAL STIMULI ACTING ON TRIGEMINAL PATHWAY (POINTS OF ATTENTION)
EXPLANATION OF TRIGEMINAL RECEPTORS
- Orthonasal olfaction smell through the nose
- Retronasal olfaction smell perceived via the mouth during
chewing
- Gustation 5 tastes in the mouth
- Trigeminal sensations spicy, pungent, cooling, tingling
o Also, the same mechanism used to detect
temperature change
- Trigeminal response is recorded in separate parts of the brain,
different from gustation and olfaction
- Unlike the basic tastes, sensations are registered by the
trigeminal nerve, which is also responsible for registering
mechanical and temperature stimuli in the face
- With respect to sensory perception, 2 stimuli are of importance
o Temperature
o Recognition of ‘sensation’ molecules
- There are 3 classes of sensation molecules
o Hot, spicy, pungent (chili peppers, wasabi)
o Cooling (mint)
o Tingling (Sichuan pepper)
Sensations are registered by ‘sensors’
- Similarities: 6 trans-membrane domains (shown in blue)
- Differences: terminal domain differs between ‘families’
- TRP cation channels sensing temperature and ‘sensation’
molecules
o TRP = Transient Receptor Potential
- TRP cation channels are proteins which act as a kind of
sensor
- Super-family of TRP channels divided in 7 sub-families, the
classification of which is based on amino acid sequence
similarities
- TRP channels have a conserved core flanked by subfamily-
unique domains
- Conserved core is essentially the trans-membrane domain, consisting of 6 trans-membrane
helices
, - Functional sensors are typically a tetrameric assembly forming cation-permeable pore
- Potentiated by external stimuli: tastant of change in temperature
Taste receptors can act in different fashions
Capsaicin receptor (TRPV1)
- 6 trans-membrane helices
- Tetrameric assembly
- Channel
Bitter receptor
- 7 trans-membrane helices
- Monomer
- G-protein coupled receptor (GPCR), no channel
Three sub-families of TRP channels act as trigeminal taste sensors
1. TRPV1: capsaicin (chili pepper spicy)
2. TRPA1: glucosinolates (mustard pungency)
3. TRPM8: menthol (mint cooling effect)
Mechanism of action of TRP channels
- Activation by stimulus
- Channel opens
- Influx of Ca2+, Na+ ions
- Depolarization of neuronal fibers
- Signal transduction to brain via trigeminal nerve
- Perception Figure 1: TRP channel
mechanism
Perceiving hot and cold: TRP’s with different ‘gate-keeping’ properties
- Each TRP responds (opens) to specific temperature range
- Open channel cation influx signal perception!
- By making use of different TRP’s, a range of temperatures can be perceived
- TRP’s sensitivity to temperature is related to conformational changes in the tetrameric TRP
assembly, resulting in widening (increased activity) or narrowing of the channel (decreased
activity)
- Besides, each TRP recognizes a specific set of molecules associated with taste sensations
- Binding of tastants can induce conformational changes in 4*TRP assembly, similar to temperature
,TRP activation
- Concentration expressed in log form
- From left curves you can see the levels of resiniferatoxin do not return to normal which probably
explains why it is a toxin
- In the graphs on the right you can see the curve of resiniferatoxin is shifted to the left which
means the compound is more potent at lower concentrations you will already have an
activation of the receptor
- Agonist = something that will stimulate and activate the receptor
- Antagonist = something that will bind the receptor and block its activation
- Value/parameter used to compare different compounds EC50
o The half maximum effective concentration
o Concentration required to achieve 50% response
- EC50 cannot be used when compound is toxic
Structure-function relationships in pungent compounds
- Homovanillyl group = structural motif essential for bioactivity
o Know and recognize structure for exam
Fugu: a deadly delicacy
- Japanese dish, lethally poisonous if prepared incorrectly
- Fugu = poisonous puffer fish
- Th poison is a sodium channel blocker Tetrodotoxin (TTX)
o Muscles are paralyzed
o Victim is fully conscious
o You cannot breathe anymore
- No antidote!
- The poisonous substance = tetrodotoxing (TTX)
o Various structural analogues of TTX present in puffer fish
o The puffer fish itself is not sensitive to its toxin, because it
has a mutation in receptor and as a result the toxin cannot
bind
, - Some look-alikes are TTX are non-toxic
- TTX mainly accumulates in the ovaries and the liver of the puffer fish
o In preparation of fugu contamination of these organs should be carefully excluded
Breeding non-toxic puffer fish
- The toxin in puffer fish seems to originate from the fish’s food supply which comprises of animals
containing tetrodotoxin-producing bacteria
- Tetrodotoxin might be produced by bacteria
- Puffer fish on a special diet seem to be non-toxin, others speculate these fish might be a different
variety
HOT/SPICY SUBSTANCES FROM PEPPERS, GINGER, MUSTARD, GARLIC, ONION
- Chili heat scale is given in Scoville units
- Capsaicin = compound responsible for spicy sensation
Capsaicin look-alikes
- Homo vanillyl group present on all capsaicinoids and is the
structure recognized by the TRPV1 receptor
- Chili peppers contain a large collection of capsaicinoids of
which capsaicin and dihydrocapsaicin contribute most to
pungency
- Structural variation resides in the alkyl chain
o All capsaicinoids contain homo vanillyl group which
is bound to alkyl moiety through amide bond
Sweet chili peppers contain capsiate
- Capsaicin: homo vanillyl group bound to alkyl moiety through amide bond spicy
- Capsiate: homo vanillyl group bound to alkyl moiety through ester bond sweet, non-spicy
- Capsiate seems to be unstable in aqueous environment
Black/white/green/red peppercorns
Black (Piper nigrum)
- Full-grown green berry
- Dried after heat treatment during which browning enzymes are released
White (Piper nigrum)
- Red-ripe berry
- Dried after removal of outer pericarp layer
Green (Piper nigrum)
- Full-grown green berry
- Sun-dried or freeze-dried
Pungent compounds in Piper nigrum peppercorns class of compounds called PIPERAMIDES
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