The main volatiles responsible for the clustering included organic acids such as propanoic, butanoic, and heptanoic acids
; alcohols such as linalool, benzeneethanol, 2,3-butanediol, cyclohexanol, 2-heptanol, 2-octanol, and 3-octen-1-ol; aldehydes and ketones such as 1-phenyl ethenone, 2-undecanone, and butanal; esters like 2-pentanol acetate, hydrocarbons such as nonacosane and 1,3 cyclohexadiene, among others (Figure 2).
The SCFA (acetic, propionic, isobutyric, butyric, isovaleric, valeric, and caproic acids) and one MCFA (medium chain fatty acid, heptanoic acid
) in the intestinal content (caecum, proximal and distal colon) were analysed using a GLC method .
Pentaenoic and heptanoic acid
(Sigma Chemical Co., Aberdeen, UK) were used as internal standards during fatty acid analysis.
Table 1 Typical trigeminal stimulants Volatile stimulants (1) Water-soluble stimulants Octanol Capsaicin (2) Nicotine Piperine (2) Heptanol Zingerone (2) Hexanol Eugenol (2) Octanoic acid Allyl-isothiocyanate (2) Heptanoic acid
Dihydrocapsaicin (3) [alpha]-Terpineol Nordihydrocapsaicin (3) l-Carvone Homocapsaicin (3) Butyric acid Homodihydrocapsaicin (3) Pentanol Resiniferatoxin (3) Acetic acid Isovelleral (3) Diethylamine Scutigeral (3) Cyclohexanone Capsazepine (3) Benzaldehyde Ovanil (3) Benzyl acetate Valeric acid Formic acid Butanol Amyl acetate Ethanol Propanol Limonene Butyl acetate Toluene Methanol (1) Bryant and Silver (2000); in order of increasing threshold.