The Chemical Structure of the Capsaicinoids

Chemical structure of Capsaicin
(For those with graphic-impaired viewers, an ascii version is also available)

Capsaicin, also known as N-Vanillyl-8-methyl-6-(E)-noneamide, is the most pungent of the group of compounds called capsaicinoids isolated from peppers. It is sparingly soluble in water, but very soluble in fats, oils and alcohol. The second most common capsaicinoid is Dihydrocapsaicin:

Chemical structure of Dihydrocapsaicin [ascii]

Capsaicin and Dihydrocapsaicin together make up 80-90% of the capsaicinoids found in the fruit. In C. annuum the total capsaicinoid content ranges from 0.1 to 1.0%, and the capsaicin:dihydrocapsaicin ratio is about 1:1. In C. frutescens(Tabasco peppers) the total content ranges from 0.4-1.0% with the ratio around 2:1.

The minor capsaicinoids include Nordihydrocapsaicin [Dihydrocapsaicin with (CH2)5 instead of (CH2)6], Homocapsaicin [Capsaicin with (CH2)5 instead of (CH2)4], and Homodihydrocapsaicin [Dihydrocapsaicin with (CH2)7 instead of (CH2)6].

The pungencies of these five pure compounds in Scoville Units (SU) are as follows:

        Compound        Pungency x 100,000 SU
   
        Capsaicin               160
        Dihydrocapsaicin        160
        Nordihydrocapsaicin      91
        Homocapsaicin            86
        Homodihydrocapsaicin.    86

From: Govindarajan, VS and Sathyanarayana, MN; Capsicum - Production, Technology, Chemistry and Quality. Part V. Impact on Physiology, Nutrition and Metabolism; Structure, Pungency, Pain and Desensitization Sequences, Crit. Rev. Food Sci. Nutr. 29, 435. 1991

There are also 2 minor homologs and three analogs with straight alkyl chains that exist in nature.