Mapping metabolome changes in Luffa aegyptiaca Mill fruits at different maturation stages via MS-based metabolomics and chemometrics

Abstract

Introduction: Luffa aegyptiaca Mill, sponge gourd or Egyptian cucumber, is grown worldwide for its edible fruit consumed as a vegetable like cucumber. Unlike young fruit (YF), the fully mature ripened fruit (MF) is strongly fibrous and is used as a cleanser to make scrubbing bath sponges. YF undergoes a complex series of physiological and biochemical changes during fruit ripening. However, the chemical compositional differences between YF and MF in Luffa aegyptiaca have not been distinguished to date.

Objectives: Comprehensively compare the metabolites profile of YF and MF to give insight on how maturation stage affects chemical composition.

Methods: Mass-based metabolomics comprising GC/MS and UHPLC/MS were adopted in this study targeting its volatile and non-volatile metabolites coupled with chemometrics to rationalize for the differences.

Results: A total of 53 volatile metabolites were identified via headspace solid phase microextraction (SPME) comprising 66.2% aldehydes/furans, 51.6% alcohols, 38.2% ketones, 15.1% acids and 10.1% aromatics of which aldehydes/ furans were dominant at both fruit stages. Young fruit was in general more erniched in metabolites as revealed from UHPLC/MS and GC/MS analyses. The YF group encompassed higher levels of short chain alcohols (1-octen-3-ol) and aldehydes ((E)-2-hexenal and cucumber aldehyde) in addition to terpenoids (linalool). In contrast, fatty acids (octanoic acid) predominated MF specimens. UHPLC/MS analysis revealed for several oleanene triterpene glycosides as major secondary bioactive compounds, dihydroxy-oxo-oleanenoic acid glycoside found more abundant in YF versus MF as revealed from multivariate data analyses.

Conclusions: Our results reveal for the distinct metabolite changes in L. aegyptiaca fruit in its different stages and to rationalize for its different usage.

Keywords: GC/MS; Luffa aegyptiaca; Metabolomics; SPME; UHPLC/MS.

Graphical abstract

Fig. 1

A photo of L. aegyptiaca fruit collected at the 2 different ripening stages (YF) and (MF).

Fig. 2

SPME-GC–MS chromatograms of headspace volatiles collected from young (YF) and old mature (MF) L. aegyptiaca fruit.

Fig. 3

Principal component analysis (PCA) and orthogonal projection to latent structures-discriminant analysis (OPLS) supervised data analysis of modelling youngversus old mature fruit specimens analysed via SPME GC–MS for their volatile metabolites. PCA score (A) and loading plot (B) (n = 3); OPLS-DA score plot (C) and loading S-plot (D). Segregation in both score plots showed enrichment of alcohols, aldehyde and ketone compounds in young fruit.

Fig. 4

UHPLC-MS base peak chromatograms of secondary metabolites analysed from young (YF) and old mature (MF) L. aegyptiaca fruit.

Fig. 5

Principal component analysis (PCA) and orthogonal projection to latent structures-discriminant analysis (OPLS) supervised data analysis of modelling young versus mature fruit specimens analysed viaUHPLC-MS for their secondary metabolites. PCA score (A) and loading plot (B) (n = 3); OPLS-DA score plot (C) and loading S-plot (D). Segregation in both score plots showed marker metabolites for YF as Mol.ion/Rt, namely: Lucyoside I (649.39/11.9), Dihydroxy-23-oxo-12-oleanen-28-oic acid-O-dipentosyl deoxyhexosyl-O- hexosyl glucuronoside (1233.54/11.21); Dihydroxy-23-oxo-12-oleanen-28-oic acid-O-deoxyhexosyl-hexoside (793.43/11.78) and Dihydroxy-23-oxo-12-oleanen-28-oic acid-O-pentosyl dihexoside (941.5/11.35).

Fig. 6

Structures of major secondary metabolites detected by UHPLC/MS and discussed throughout the manuscript.