Stability of capsinoid in various solvents.

To investigate the stability of capsinoid in solvents, the quantitative change of vanillyl nonanoate, a synthetic model capsinoid, in various solvents was measured by HPLC. Vanillyl nonanoate was stable in nonpolar solvents, whereas it was labile in polar solvents. In particular, vanillyl nonanoate tended to decompose in protic solvents such as alcohol and water. Structures of the decomposition products from vanillyl nonanoate in methanol and ethanol were determined to be methyl and ethyl vanillyl ethers, respectively. To clarify the decomposition mechanism of capsinoid, six analogues of vanillyl nonanoate were tested. The stability of the analogues in organic solvents suggested that the hydroxyl group in the para-position of the benzene ring largely contributes to the decomposition of capsinoid.