The Combinatorial Chemistry of Flavor

Spectroscopy-Microscopy-Spectrum-v4

Taste is only one component of the flavor of food, with others including:

  • texture: gritty vs.  greasy vs. dry
  • aroma:  see post on Food Aroma Chemistry
  • temperature“:  the cooling of mint vs. the heat of chilis

As an aspiring cook, I have found it helpful to summarize the chemistry behind each part of a foods flavor so that I can better understand how to control each of these variables. In the figure above I have summarized the chemical basis for each type of “taste” and food’s that represent characteristic combination.

TASTE

The five “tastes” (savory, sweet, sour, salty, bitter) are induced by five different cell-types spread across the surface of your tongue (the “taste map” of the tongue is just an urban legend) in clusters called taste-buds (see figure above). Each of these cells expresses a specific type of receptor which is able to bind to only one type of tastant (taste molecule).   Below I summarize key information on each receptor ranging from practical (how increase or decrease) to technical (potency of tastant).

SWEET: general marker for nutritional content: carbohydrates (more = better)

  • FOODS:  fruits
  • TASTANT: sugars (sucrose, fructose, glucose)
  • RECEPTOR:  T1R2/T1R3 (a G-protein coupled receptors (GCPR’s) dimer)
  • SENSITIVITY:  millimolar EC50
  • TO INCREASE: add sugar or honey
  • TO MASK:  add lemon juice (sour) or cayenne pepper (heat)

SAVORY: general marker for nutritional content: protein (more = better)

  • FOODS:  meats, seaweed
  • TASTANT: L-amino-acids (L-glutamate in particular)
  • RECEPTOR:  T1R1/T1R3 (a G-protein coupled receptors (GCPR’s) dimer)
  • SENSITIVITY:  millimolar EC50
  • TO INCREASE: add soy sauce or MSG
  • TO MASK:  dilute

SOUR: general marker for acidity (moderate amount optimal)

  • FOODS:  citrus
  • TASTANT: protons
  • RECEPTOR:  PKD2L1 (a ion channel)
  • SENSITIVITY:  EC50 = 1mM  (pH = 3)
    • sour: Lime juice/Vinegar pH = 2-3
    • slightly sour: Orange/Apple Juice pH = 3-4
    • not sour: tomato(pH 4-5), sugar(pH 5-6), milk (pH 6-7)
  • TO INCREASE: add lemon juice, vinegar
  • TO MASK:  add sugar (sweetness)

SALTY: general marker for sodium (moderate amount optimal)

  • FOODS:  meats/eggs
  • TASTANTsodium salts
  • RECEPTOR:  ENaC (an ion channel)
  • SENSITIVITY:  EC50 = 5 mM  
  • TO INCREASE: add salt, MSG
  • TO MASK:  add sugar (sweetness)

BITTERNESS: general marker for toxicity (low amount optimal)

  • FOODS:  plant materials: tea, coffee, chocolate
  • TASTANT: drug-like small molecules: polycyclic amines, carbonyls and phenols (membrane permeable)
  • RECEPTOR:  >30 different T2R GCPR’s (detects broad range of compounds)
  • SENSITIVITY:  EC50 = micromolar (very sensitive to low amounts of “toxins”)
  • TO INCREASE: add quinine, cocoa
  • TO MASK:  add sugar (sweetness) or salt 

 

TEXTURE / MOUTH-FEEL


Mouth-feel describes the mechanical or tactile sensation that a food confers to the inner-surface of the mouth. At one extreme, fatty foods coat the mouth with oil and convey a greasy or smooth association with food (e.g. milks). At the other extreme, astringent foods like tea or wine induce a dry or puckering sensation because they “de-grease” the surface of them mouth by “brushing” away mucus with their large water-soluble polymers such as tannins. This “de-greasing” can have a pallate cleansing effect which is presumably why “astringents” like tea or wine are often paired with fatty dishes such as desserts or meats.

 

TEMPERATURE

Certain chemicals are able to “trick” temperature sensing receptors into turning on and this is responsible for the hot or cooling sensations associated with different foods. At one end of the spectrum, cooling molecules such as menthol activate the cold sensitive ion channel: TRPM8.  At the other end of the spectrum hot molecules such as capsaicin activate the heat sensitive ion channel: TRPV1.

 

REFERENCES:

  1. McGee, Harold. 1984. On Food and Cooking. New York, NY. Scribner pp. 272-274,389-400.
  2. Potter, Jeff. 2010. Cooking for Geeks: Real Science, Great Hacks, and Good Food. O’Reilly Media
  3. Yarmolinsky, David A; Zuker, Charles S; Ryba, Nicholas J P; Common sense about taste: from mammals to insects. Cell, 2009, 139, 234-244.
  4. Beliz, H.; Wieser, H. Bitter compounds: Occurrence and structure‐activity relationships. Food Reviews International, 1985, 1, 271-354.
  5. Ishimaru, Y.; Inada, H.; Kubota, M.; Zhuang, H.; Tominaga, M.; Matsunami, H.  PNAS, 2006, 103, 12569-74.
  6. Alvarez, D.; Rosa, D.; Navarro-gonzález, J. F.; Giraldez, T. ENaC Modulators and Renal Disease, Current Mol. Pharm., 2013, 6, 35-43.
  7. Stokes, J. R.; Boehm, M. W.; Baier, S. K. Oral processing, texture and mouthfeel: From rheology to tribology and beyond. Curr. Op. Coll. Inter. Sci., 2013, 18, 349-359.
  8. des Gachons, C. P.; Mura, E.; Speziale, C.; Favreau, C. J.; Dubreuil, G. F.; Breslin, P. S.  Current Biology, 2012, 22, R829-R830.

 

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