Plant-Wide Target Metabolomics Provides a Novel Interpretation of the Changes in Chemical Components during Dendrobium officinale Traditional Processing

Abstract

The traditional processing of Dendrobium officinale (DO) is performed in five necessary processing steps: processing fresh strips, drying at 85 °C, curling, molding, and drying at 35 °C (Fengdou). The antioxidant activity of DO is increased after it is processed into Fengdou. To comprehensively analyze the changes in the functional components, a plant-wide target metabolomics approach was employed. In total, 739 differential chemical components were identified in five processing treatments, mainly highlighting differences in the levels of phenolic acids, flavonoids, lipids, and amino acids and their derivatives, and the glycosylation of aglycone resulted in the upregulation of flavonoid glycoside levels. Temperature is a key factor in DO processing during production. In addition, the enrichment of specific differential chemical components was found mainly in five different metabolic pathways: glucosinolate biosynthesis, linoleic acid metabolism, flavonoid biosynthesis, phenylpropanoid biosynthesis, and ubiquinone and other terpene quinone biosynthesis. A correlation analysis clarified that total phenols and flavonoids show a significant positive correlation with antioxidant capacity. This study provides new insights into the influence of the processing processes on DO quality, which may provide guidance for the high-quality production of DO.

Keywords: Dendrobium officinale; antioxidant activity; chemical compositions; traditional processing; widely targeted metabolic analysis.

Figure 1

Appearances of DO samples at the end of each processing step. The fresh strip (FA1), drying at 85 °C (FB2), curling (FC3), molding (FD4), and drying at 35 °C (FE5).

Figure 2

The DPPH scavenging capacity (A) and ABTS scavenging capacity (B) of DO samples in different processes; the contents of total phenols (C) and flavonoids (D) of DO samples in different processes.

Figure 3

Classification of the 1182 composition of DO samples (A); PCA score plot (B). The sampling groups were color-coded as follows: green, FA1; orange, FB2; purple, FC3; pink, FD4; blue, FE5; red, QC. Correlation diagram of composition of different processes of DO (C).

Figure 4

Volcano plots of the differential ingredient expression levels between FA1 vs. FB2 groups (A), the FB2 vs. FC3 groups (B), the FC3 vs. FD4 group (C) and the FD4 vs. FE5 group (D), red indicating upward and green indicating downward; Venn diagram illustrating the overlapping and specific differential compositions for four comparison groups (FA1 vs. FB2, FB2 vs. FC3, FC3 vs. FD4, FD4 vs. FE5) (E).

Figure 5

Correlation heatmap of specific differential compositions and antioxidant activity. TPC: total phenolic content; TFC: total flavonoid content; DPPH: DPPH·scavenging capacity; ABTS: ABTS + scavenging capacity.

Figure 6

Differences in the relative contents of the main differential chemical composition in the different processing procedures of DO. To reduce the influence of concentration on pattern recognition, the peak area matrix is normalized. Bar charts show the relative content of vanillin (A), syringaldehyde-4-O-glucoside (B), syringaldehyde (C), methyl syringate (D), syringic acid (E), coniferyl alcohol (F), phloretin-4′-O-glucoside (G), 4′-O-glucosylvitexin (H), and isosaponarin (I).

Figure 7

The alteration of the flavonoid pathway (A) and relative amount (B) during the processing of DO. To reduce the influence of concentration on pattern recognition, the peak area matrix is normalized in relative amount (B).