Elsevier

Food Chemistry

Volume 298, 15 November 2019, 125063
Food Chemistry

Short communication
NMR-based metabolomics approach to investigate the distribution characteristics of metabolites in Dioscorea opposita Thunb. cv. Tiegun

https://doi.org/10.1016/j.foodchem.2019.125063Get rights and content

Highlights

  • A metabolomics study of Dioscorea opposita Thunb. cv. Tiegun exclude-peel and peel.

  • Two different metabolic profiles were compared by NMR-based metabolomics approach.

  • 13 characteristic metabolites responsible for good separation were identified.

  • Distribution of metabolites in Dioscorea opposita Thunb. cv. Tiegun was defined.

Abstract

Dioscorea opposita Thunb. cv. Tiegun (DTT), a type of homologous medicinal plant, is commonly used as food in daily life. However, there has always been confusion regarding removal of the peel, as the nutrient metabolite composition of the peel is unclear. Here, a nuclear magnetic resonance (NMR)-based metabolomics approach was used to determine the metabolite distribution in DTT exclude-peel and peel. Thirteen characteristic metabolites with statistical significance were identified and compared using multivariate, univariate and cluster analyses. The results demonstrated that the peel contained the higher levels of α-glucose, batatasin IV, batatasin I, asparagine, β-glucose, protodioscin, threonine, protogracillin, dioscin, and β-sitosteryl acetate, and the samples without the peel had the higher levels of leucine, glutamine and alanine. This study provided scientific data for understanding the distribution characteristics of metabolites in DTT samples, promoting reasonable consumption of DTT.

Introduction

Dioscorea opposita Thunb. (Huai Shan Yao), a plant used both as a medicine and a food, is an important yam species. This plant contains many nutritional metabolites, such as amino acids, organic acids, sugars, polysaccharides, batatasins, dioscins, and allantoin. These metabolites have shown effectiveness in invigoration of the spleen and stomach, tonification of the kidney, moistening of lung tissue, and promotion of bodily fluid production (Wang et al., 2006). Wen county of Jiaozuo city (Henan Province, China) is famous for planting Huai Shan Yao for more than 2000 years. It has been shown that Dioscorea opposita Thunb. cv. Tiegun (DTT) has the best quality, and this plant has been used daily as not only a popular food but also an important invigorant in traditional Chinese medicine (Yang et al., 2017, Zhou et al., 2011, Zhou et al., 2014). Currently, DTT is prepared for consumption in different ways, including boiled, steamed, or fried. Regardless of the method of preparation, whether it is nutritionally/medicinally beneficial to include or exclude the peel of DTT remains unclear. Previous research on DTT has mainly focused on the extraction of specific components (Feng, 2008) and the problem of browning during the processing of fresh-cut slices (Zhao et al., 2009, Zhao et al., 2008). However, the distribution of metabolites in exclude-peel and peel of DTT remains entirely unclear.

Metabolomics is a powerful tool for obtaining comprehensive information regarding the biochemical constituents of a biological system, and this method can directly capture subtle changes that reflect the physiological status of an organism (Nicholson & Wilson, 2003). In recent years, metabolomics has rapidly emerged as an effective approach in the food science field and has been used to assess the quality, authenticity, and safety of food products (Ordoudi et al., 2015). This approach has also been used to identify the geographical origins of different samples (Klockmann, Reiner, Cain, & Fischer, 2017) and to identify changes caused by external or internal environmental stimuli (An et al., 2018). Furthermore, metabolomics has also shown unique advantages in the study of pharmaceutical and edible homologous foods, especially in the discovery of potential biochemical and nutritional value (Li et al., 2017). Nuclear magnetic resonance (NMR) spectroscopy is one of the most widely employed analytical tools in metabolomics studies because this tool is non-destructive, rapid, and requires relatively simple sample preparation (Zhu, Wang, & Chen, 2017). NMR-based metabolomics studies can identify common constituents and valuable active ingredients, making it a powerful method by which to obtain comprehensive information for quality evaluation. This method also allows for better definition of the characteristic biochemical constitutions being studied (Farag, Labib, Noleto, Porzel, & Wessjohann, 2018).

In this study, NMR-based metabolomics approach was utilized to acquire global profiles and identify potential characteristic metabolites of DTT exclude-peel and peel samples. The objective of this study was: i) to identify the characteristic metabolites in DTT exclude-peel and peel samples and ii) to define the distribution of nutritional components in DTT. An overview of the experimental procedure was shown in Supplementary Fig. S1.

Section snippets

Chemicals and reagents

Monosodium phosphate (NaH2PO4) and disodium phosphate (Na2HPO4) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Methanol and acetonitrile (gradient-grade for liquid chromatography) were purchased from Millipore Corp. (Billerica, MA, USA), and formic acid and ammonium hydroxide solution were purchased from CNW Technologies GmbH (Duesseldorf, Germany). Deuterium oxide (D2O, 99.9 atom % D) containing 3-(trimethylsilyl) propionic-2, 2, 3, 3-d4 acid sodium salt (TSP,

Metabolic profiling of Dioscorea opposita Thunb. Cv. Tiegun extract

Representative 1H NMR spectra of DTT extracts from DEG and DPG samples were shown in Fig. 1 with a total of 42 labelled metabolites. Detailed information regarding these metabolites, including chemical shifts and peak multiplicity, was provided in Supplementary Table S1. These metabolites were identified by referring to previous literature (Bai et al., 2008, Coxon et al., 1982, Hashimoto and Tajima, 1978, Hashimoto et al., 1974, Liang et al., 2012, Ruan et al., 2016); 1H–1H COSY, HMBC and HSQC

Conclusion

NMR-based metabolomics approach was demonstrated to be a powerful analytical tool for the investigation of the metabolite distribution in DTT. This approach confirmed the characteristic metabolites of the DEG and DPG samples on a comprehensive scale. This study also offered fresh insights into the evaluation of the nutritional value of medicine-food homology, further providing scientific data for dietary improvement.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgements

This study was supported by the Science-Technology Foundation for Outstanding Young Scientists of Henan Academy of Agricultural Sciences (grant no. 2018YQ22) and the Province Foundation for Science Innovation Distinguished Young Scholars of Henan Province (grant no. 184100510015).

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