Non-targeted metabolomic analysis for the comparative evaluation of volatile organic compounds in 20 globally representative cucumber lines

Abstract

Volatile organic compounds (VOCs) are one of the main fruit-quality determinants in cucumber. Here, we investigated the differences in the VOC and primary metabolite composition among 20 representative cucumber lines. Results of non-targeted metabolomics revealed that the cucumber breeding line of the Korean group showed a unique VOC composition in the fruit peel compared to the other groups. Fruit-flesh VOCs significantly differed among Korean, European, and Thai fruits. The main cucumber flavor components, 2-hexenal, hexanal, 6-nonenal, 2,4-nonadienal, and 2,6-nonadienal, were lower in the Korean cucumber lines than in the others. Conversely, linoleic acid derivatives and α-linolenic acid, which are precursors of these VOCs, were abundant in Korean cucumber line. This suggests that the metabolism related to the characteristic flavor of cucumber are downregulated in Korean cucumber line. This study provides novel insights into the fruit flavor-associated metabolome in various cucumber lines.

Keywords: Metabolomics; cucumber; fruit flavor; hydroperoxide lyase (HPL) and lipoxygenase (LOX) metabolisms; volatile organic compounds.

Figure 1

Immature fruits of the representative 20 cucumber breeding lines evaluated in this study.

Figure 2

PCA and PLS-DA score plots of 20 cucumber breeding lines of peel (A–C) and flesh (D–F) based on HS-SPME-GC-TOF-MS data set. (A, B, D, E) indicate the color of sample line. (C, F) indicate the color of sample group. , peel; , flesh.

Figure 3

PLS-DA score plots of different three cucumbers based on SPME-GC-TOF-MS (A, B) and GC-TOF-MS (C, D) data set. (A, C) are the results of analyzing different peel data. (B, D) are the results of analyzing different flesh data. Different sample symbolized as: Peel (: SJ24 (Korea group), : SJ62 (Europe group), : SJ109 (Thailand group)), flesh (: SJ24 (Korea group), : SJ62 (Europe group), : SJ109 (Thailand group)).

Figure 4

Schematic diagram of the biosynthetic pathway and relative content of metabolites in SJ24, SJ62, and SJ109 cucumbers. The pathway was modified from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database (http://www.genome.jp/kegg/). The colored squares (blue-to-red) represent the relative abundance.