Composition of the surface waxes from bell pepper and eggplant

Abstract

Surface waxes from the skins of bell pepper (Capsicum annuum) and eggplant (Solanum melongena) were rinsed with tert-butylmethyl ether (TBME). The wax components were separated into two fractions by elution from a small silica gel column with toluene/hexane (2+1) followed by methanol. They were identified by GC/MS and quantitatively determined by GC/FID. For 12 bell pepper cultivars, fraction 1 made up 39% of the total and contained mainly n-alkanes C₂₀−C₃₅ (with C₃₁ dominating), iso-alkanes C₂₅−C₃₅, and some aldehydes. The 61% of fraction 2 consisted of 15 triterpenes, namely α- and β-amyrin, lupeol, glutinol, 3β-friedelanol, friedelin, taraxerol, taraxasterol, δ-amyrin, germanicol, multiflorenol, ω-taraxasterol, isomultiflorenol, isobauerenol and bauerenol, as well as n-alkanoic acids C₁₆−C₃₂, 2-hydroxy-alkanoic acids C₂₀−C₂₆ and traces of n-alkanols and phytosterols (campesterol, stigmasterol and β-sitosterol). For the three eggplant cultivars, 77% of fraction 1 was obtained with (in decreasing order) n-alkanes C₂₃−C₃₆, anteiso-alkanes C₂₉−C₃₆, iso-alkanes C₂₇−C₃₅, and some aldehydes. In the 23% of fraction 2, the n-alkanoic acids C₁₆−C₃₂ predominated compared with the 2-hydroxy-alkanoic acids C₂₂–C₂₆, the n-alkanols C₂₄–C₂₉, triterpenols (α- and β-amyrin, lupeol, germanicol) and sterols (stigmasterol and β-sitosterol).