Nutritional Characterization and Untargeted Metabolomics of Oyster Mushroom Produced Using Astragalus membranaceus var. mongolicus Stems and Leaves as Substrates

Abstract

Astragalus membranaceus var. mongolicus (AMM) is an edible and medicinal material and is commonly used in East Asia. According to the pharmacopeia of China, the dried root of AMM is medicinal. However, the aerial parts of AMM are always directly discarded after harvest. The stems and leaves are also rich in active compounds, including saponins, flavonoids, terpenoids, and polysaccharides. To rationally use resources, waste products from AMM stems and leaves are useful substrates for edible fungus cultivation. Here, oyster mushroom (Pleurotus ostreatus var. florida) was cultivated on a basal substrate supplemented with AMM stems and leaves (AMM group). The nutritional and chemical composition of the fruiting body were analyzed by metabolomics and chemometrics. Our results showed that AMM addition to the substrate affected the fresh weight, moisture, fat, protein, and element concentrations, and amino acid composition of oyster mushroom. Moreover, 2,156 metabolites were detected and annotated based on the metabolomics data, of which 680 were identified as differentially expressed metabolites. Many active phytometabolites previously identified in AMM herbs were also detected in the metabolomics of oyster mushroom from AMM group, including 46 terpenoids, 21 flavonoids, 17 alkaloids, 14 phenylpropanoids, and 3 fatty acids. In summary, our results imply that oyster mushroom cultured with AMM stems and leaves might have very high nutritional therapy health care value.

Keywords: Astragalus membranaceus var. mongolicus; Pleurotus spp.; nutrition; stems and leaves; untargeted metabolomics.

FIGURE 1

The fruiting body of P. ostreatus var. florida used in this study. (A) Sample from control group; (B) sample from AMM group.

FIGURE 2

PAC (A), PLS-DA (B), OPLS-DA (C) score plots and OPLS-DA model permutation test (D) of metabolites for comparison between AMM and control group.

FIGURE 3

Functional classification and annotation of differential metabolites identified in the comparison between AMM and control group. (A) The KEGG classification of differential metabolites; (B) KEGG pathway enrichment of differential metabolites.

FIGURE 4

Classification and identification of differential phytometabolites. (A) Differential phytometabolites in our study and major phytometabolites in AMM herbs; (B) product ion mass spectra of [M + H]⁺ ion of astragaloside IV; and (C) chromatography peak of a representative AMM (1.31 min, astragaloside IV) and control sample.