Overview of Major Capsaicinoids, Page 2

Introduction
Capsaicin
Dihydrocapsaicin
The Difference Between Capsaicin and DHC
Cis/Trans Isomerism in Capsaicin

Previous (Introduction)

The Capsaicin Molecule
Common name: Capsaicin
Semi-systematic names: N-vanillyl-8-methyl-6-(E)-nonenamide; trans-N-vanillyl-8-methyl-6-nonenamide; vanillylamide of 8-methylnon-trans-6-enoic acid
Systematic name: N-(4-hydroxy-3-methoxybenzyl)-8-methylnon-trans-6- enamide
CAS Number: 404-86-4
Molecular formula: C₁₈H₂₇NO₃
Molecular weight: 305.42
Melting point: 65 ^oC (Ref 8, 1811)
Boiling point: 210-220 ^oC at 0.01 torr pressure (Ref 8, 1811)
UV maxima: 227 nm, 281 nm (Ref 8, 1811)
Solubility: freely soluble in ethanol, ether, benzene, chloroform; slightly soluble in carbon disulfide; insoluble in water (Ref 8, 1811)

Detection Threshold: 26.35 ± 2.98 million Scoville Heat Units (SHU) [=] mL/g (Ref 9, 903). The detection threshold is the lowest concentration of capsaicinoid (in SHU, or mL/g) at which a sample of standard sugar water containing a capsaicinoid can be differentiated by taste (organoleptic evaluation) from a blank sample of standard sugar water. As 1 SHU = 1 mL/g, this means that the subjects in the study, on average, were able to tell a solution containing 1 gram of capsaicin in 26.35 million mL of standard sugar water (about 7000 gallons) apart from plain sugar water by taste. If the density of water is taken to be 1 g/mL, this solution would be 0.000003795% by weight capsaicin.

Pungency Threshold: 16.35 ± 2.28 million SHU (Ref 9, 904). The pungency threshold is the lowest concentration of capsaicinoid in a standard sugar water solution (in SHU, or mL/g) at which a "distinct sensation of pungency" is noted during organoleptic evaluation. 16.35 million SHU is equivalent to 1 gram of capsaicinoid in about 4315 gallons of sugar water, or a 0.000006116% by weight solution of capsaicinoid. Other studies have determined different pungency thresholds for capsaicin; reported values range from 9.2 million to 17.0 million SHU (Ref 9, 902)

Huh?!? Since Merck lists capsaicin as being insoluble in water, just how, you may ask, are these sugar-and-fire water concoctions prepared for these tests? Especially at such ridiculously low concentrations, like a gram in a 5000 gallon zoo-sized aquarium! Good question! If you want to know the answer, read about serial dilution.

Type of pungency: In a detailed study performed by Anna Krajewska and John Powers (Ref 9), subjects noted that very dilute solutions of the various capsaicinoids produced different types of pungency. These differences were not noted using more concentrated solutions. Capsaicin, in a very dilute solution, was noted as producing a "sharp and stinging bite" located "in the mid-mouth and mid-palate as well as the throat and the back of the tongue" that developed quickly and was long-lived (Ref 9, 904).

Major molecular features that determine chemical behavior:

Feature	Name or Description	Implication	Learn More
C=C	carbon-carbon double bond	Subject to at least some reactions typical of alkenes; cis/trans isomerism	Learn more about alkenes
R-NH-(C=O)-R'	secondary amide	Subject to reactions typical of secondary amides	Learn more about amides
ring: C6H3	tri-substituted benzene ring	Subject to at least some reactions typical of substituted benzene rings
Ring-OH	phenol	Subject to at least some reactions typical of phenols	Learn more about alcohols
R-O-R'	ether	Subject to at least some reactions typical of ethers	Learn more about ethers

All Learn More links point to an *excellent* online chemistry tutorial at The University of Akron.

Next (Dihydrocapsaicin)
All of the chemical structures and reaction mechanism diagrams used in this section are my own creations. None of the chemical structures that I've seen on any other Chile Head sites show unshared electrons, nor do they properly depict the unsaturation in the capsaicin molecule, both of which are major determinants of the chemical behavior of capsaicin. Due to the use of a really cheesy red-gold Chrome effect, all of my technical artwork is readily identifiable (and hopefully too ugly to steal). If you see someone else using my artwork without giving proper credits, please 1) give them a boot in the rear via email, and/or 2) let me know about it so I can do the same.


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