| Abstract
| - The pungent compounds piperine and isomers thereof, secondary metabolites present in black andwhite pepper fruit, undergo light-induced isomerizations. To facilitate studies in this area, an HPLCmethod has been developed for analysis and isolation of the following four possible piperine-derivedphotoinduced isomers: piperine, isopiperine, chavicine, and isochavicine. The limits of detection (LOD)estimated from calibration plots were ∼15−30 ng for each isomer. Reproducibilities of the analyseswere excellent, and recoveries of spiked samples were as follows (average ± SD; n = 3): chavicine,98.4 ± 2.1%; isopiperine, 96.2 ± 3.2%; piperine, 104 ± 3.8%; isochavicine, 98.9 ± 3.0%. To determinethe kinetics of these isomerizations, fluorescent light, sunlight, and UV radiation at 254 nm was usedto induce cis−trans geometric isomerization as a function of light intensities and time of exposuredetermined with the aid of high-performance liquid chromatography (HPLC) and liquid chromatographywith diode array UV detection−mass spectrometry (LC-DAD/MS). HPLC was also used to determinethe distribution of the isomers in four commercial ground black pepper products used as spices inculinary practice. Isomerization increased with light intensities and time of exposure and leveled offat the so-called photostationary phases. The piperine levels of the four products were quite similar,ranging (in wt %) from 10.17 to 11.68. The amounts of the other three isomers ranged from 0.01 to0.07 of the total for chavicine; from 0.15 to 0.23 for isopiperine; and from 0.37 to 0.42 for isochavicine.The results establish the utility of the HPLC method for simultaneous analysis of the four isomersboth in pure form and in black pepper extracts. The dietary significance of the results is discussed. Keywords: Piperine; isopiperine; chavicine; isochavicine; black peppers; photoisomerization; HPLC;LC−MS
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