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Food chemistry summary Molecular Gastronomy (FPH20806) €5,49
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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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  • 8 oktober 2021
  • 38
  • 2020/2021
  • Samenvatting
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Alisongeorgala
TASTE SENSATIONS
Five 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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