Determining the changes in metabolites of Dendrobium officinale juice fermented with starter cultures containing Saccharomycopsis fibuligera FBKL2.8DCJS1 and Lactobacillus paracasei FBKL1.3028 through untargeted metabolomics

Abstract

Background: The present study aimed to investigate the changes in volatile components and metabolites of Dendrobium officinale (D. officinale) juice fermented with starter cultures containing Saccharomycopsis fibuligera and Lactobacillus paracasei at 28 ℃ for 15 days and post-ripened at 4 ℃ for 30 days using untargeted metabolomics of liquid chromatography-mass spectrometry (LC-MS) and headspace solid-phase microextraction-gas chromatography (HS-SPME-GC-MS) before and after fermentation.

Results: The results showed that the alcohol contents in the S. fibuligera group before fermentation and after fermentation were 444.806 ± 10.310 μg/mL and 510.999 ± 38.431 μg/mL, respectively. Furthermore, the alcohol content in the fermentation broth group inoculated with the co-culture of L. paracasei + S. fibuligera was 504.758 ± 77.914 μg/mL, containing a significant amount of 3-Methyl-1-butanol, Linalool, Phenylethyl alcohol, and 2-Methyl-1-propanol. Moreover, the Ethyl L (-)-lactate content was higher in the co-culture of L. paracasei + S. fibuligera group (7.718 ± 6.668 μg/mL) than in the L. paracasei (2.798 ± 0.443 μg/mL) and S. fibuligera monoculture groups (0 μg/mL). The co-culture of L. paracasei + S. fibuligera significantly promoted the metabolic production of ethyl L (-)-lactate in D. officinale juice. The differential metabolites screened after fermentation mainly included alcohols, organic acids, amino acids, nucleic acids, and their derivatives. Twenty-three metabolites, including 11 types of acids, were significantly up-regulated in the ten key metabolic pathways of the co-culture group. Furthermore, the metabolic pathways, such as pentose and glucuronate interconversions, the biosynthesis of alkaloids derived from terpenoid and polyketide, and aminobenzoate degradation were significantly up-regulated in the co-culture group. These three metabolic pathways facilitate the synthesis of bioactive substances, such as terpenoids, polyketides, and phenols, and enrich the flavor composition of D. officinale juice.

Conclusions: These results demonstrate that the co-culture of L. paracasei + S. fibuligera can promote the flavor harmonization of fermented products. Therefore, this study provides a theoretical basis for analyzing the flavor of D. officinale juice and the functional investigation of fermentation metabolites.

Keywords: D.officinale juice; Differential metabolites; Untargeted metabolomics; Volatile components.

Fig. 1

Relative volatile components of D. officinale juice before and after fermentation. (The unfermented D. officinale juice (A), S. fibuligera fermented D. officinale juice (B), L. paracasei fermented D. officinale juice (C), L. paracasei + S. fibuligera fermented D. officinale juice (D))

Fig. 2

Heat map of the volatile components in D. officinale juice with different inoculations

Fig. 3

PCA score plots for QC samples in the positive ion mode (a) and negative ion mode (b)

Fig. 4

PCA scores of different D. officinale juice samples in the positive ion mode (a) and negative ion mode (b)

Fig. 5

Plots of OPLS-DA scores for different groups of metabolites in the positive and negative ion modes a, b, and substitution tests c, d

Fig. 6

a shows the heat map of BvsA differential metabolites, b shows the heat map of CvsA differential metabolites, c shows the heat map of DvsA differential metabolites

Fig. 7

a is for the compound volcanoes of B vs. A, b is for the compound volcanoes of B vs. A, c is for the compound volcanoes of C vs. A

Fig. 8

Histogram of factors influencing the B vs. A metabolic pathway

Fig. 9

Histogram of factors influencing the C vs. A metabolic pathway

Fig. 10

Histogram of factors influencing the D vs. A metabolic pathway

Fig. 11

Differential metabolite network diagram