Determination of Phenethyl Isothiocyanate, Erucin, Iberverin, and Erucin Nitrile Concentrations in Healthy and Pieris rapae-Infected Broccoli Tissues Using Gas Chromatography-Mass Spectrometry

Abstract

Cruciferous vegetables (Brassicaceae family) are a rich source of phytochemicals, in particular glucosinolates (GLS) and their hydrolysis products, isothiocyanates and nitriles. These phytochemicals may act as chemosensors, attracting insects, such as Pieris rapae, and stimulating oviposition. There is a lack of information on the concentrations of isothiocyanates and nitriles when an insect affects a Brassicaceae plant. In the current study, some GLS hydrolysis products were determined in healthy and Pieris rapae-infected organic cultivated broccoli plants, as well as the infesting insects’ larvae, using gas chromatography-mass spectrometry (GC-MS). This study investigated the following phytochemicals: phenethyl isothiocyanate (PEITC), erucin (ER), 3-(methylthio)propyl isothiocyanate (3MIC), and 1-cyano-4-(methylthio)butane (5MITN). All these components were quantified in the aerial and underground parts of the plants and were found in high concentrations in the roots. Among the phytochemicals studied, 5MITN presented the highest concentration in all the broccoli samples but was especially high in the stalks of the infected plants. Moreover, the analysis of a sample of Pieris rapae larvae, fed from the hosted broccoli, revealed the presence of PEITC and ER. These findings indicate that the infestation of broccoli with Pieris rapae may affect the distribution of PEITC, ER, 3MIC, and 5MITN throughout the plant. An extension of our study to conventional cultivated broccoli showed that the roots are indeed rich in GLS hydrolysis products.