Kinetics of Light-Induced Cis−Trans Isomerization of Four Piperines and Their Levels in Ground Black Peppers as Determined by HPLC and LC/MS

• Published in: Journal of agricultural and food chemistry Vol. 55; no. 17; pp. 7131 - 7139
• Main Authors: Kozukue, Nobuyuki, Park, Mal-Sun, Choi, Suk-Hyun, Lee, Seung-Un, Ohnishi-Kameyama, Mayumi, Levin, Carol E, Friedman, Mendel
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22.08.2007
• Subjects: Alkaloids - analysis; Alkaloids - chemistry; Alkaloids - radiation effects; Benzodioxoles - analysis; Benzodioxoles - chemistry; Benzodioxoles - radiation effects; Biological and medical sciences; black pepper; Chromatography, High Pressure Liquid; food composition; Food industries; Fundamental and applied biological sciences. Psychology; ground black pepper; heterocyclic oxygen compounds; high performance liquid chromatography; Isomerism; isomerization; isomers; Kinetics; Light; liquid chromatography; Mass Spectrometry; photochemistry; photoisomerization; Piper nigrum - chemistry; Piperidines - analysis; Piperidines - chemistry; Piperidines - radiation effects; piperine isomers; piperines; Polyunsaturated Alkamides - analysis; Polyunsaturated Alkamides - chemistry; Polyunsaturated Alkamides - radiation effects; reaction kinetics; Photoisomerization; Pepper; HPLC chromatography; Liquid chromatography; black peppers; Cis trans isomerization; isopiperine; LC-MS; Piperine; chavicine; Light; isochavicine; Kinetics; HPLC
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf070831p

The pungent compounds piperine and isomers thereof, secondary metabolites present in black and white pepper fruit, undergo light-induced isomerizations. To facilitate studies in this area, an HPLC method has been developed for analysis and isolation of the following four possible piperine-derived photoinduced 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 analyses were 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 determine the kinetics of these isomerizations, fluorescent light, sunlight, and UV radiation at 254 nm was used to induce cis−trans geometric isomerization as a function of light intensities and time of exposure determined with the aid of high-performance liquid chromatography (HPLC) and liquid chromatography with diode array UV detection−mass spectrometry (LC-DAD/MS). HPLC was also used to determine the distribution of the isomers in four commercial ground black pepper products used as spices in culinary practice. Isomerization increased with light intensities and time of exposure and leveled off at 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 to 0.07 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 isomers both 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