Efficient analysis of phytochemical constituents in the peel of Chinese wild citrus Mangshanju (Citrus reticulata Blanco) by ultra high performance liquid chromatography-quadrupole time-of-flight-mass spectrometry

Metabolite Variations during the First Weeks of Growth of Immature Citrus sinensis and Citrus reticulata by Untargeted Liquid Chromatography-Mass Spectrometry/Mass Spectrometry Metabolomics

Immature citruses are an important resource for the pharmaceutical industry due to their high levels of metabolites with health benefits. In this study, we used untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomics to investigate the changes associated with fruit size in immature citrus fruits in the first weeks of growth. Three orange cultivars (Citrus sinensis 'Navel', Citrus sinensis 'Valencia', and Citrus sinensis 'Valencia Late') and a mandarin (Citrus reticulata Blanco 'Fremont') were separated into eight fruit sizes, extracted, and analyzed. Statistical analyses revealed a distinct separation between the mandarin and the oranges based on 56 metabolites, with an additional separation between the 'Navel' orange and the 'Valencia' and 'Valencia Late' oranges based on 21 metabolites. Then, metabolites that evolved significantly with fruit size growth were identified, including 40 up-regulated and 31 down-regulated metabolites. This study provides new insights into the metabolite modifications of immature Citrus sinensis and Citrus reticulata in the first weeks of growth and emphasizes the significance of including early sampled fruits in citrus maturation studies.

Chemical profiling and quantification of flavones in several Pseudognaphalium and Gnaphalium species of Mexican gordolobo using UHPLC/PDA/MS

The inflorescences of the Mexican gordolobo are used as a folk medicine to treat various respiratory diseases. Currently, the botanical species that bear the name Mexican gordolobo belong to the genera Gnaphalium and Pseudognaphalium. Despite a long history of traditional use, most Mexican gordolobo species have never been fully chemically characterized, and the range of constituents in the species has not been comprehensively reported. To establish a quality control and chemical characterization method, a total of 49 samples belonging to 18 species of Pseudognaphalium and four species of Gnaphalium were studied. Nine flavones were quantified using a UPLC-PDA method. The method was validated in terms of linearity (R2 > 0.99), precision (intra- and inter-day: 0.1-3.9%), accuracy (96-103%), detection limit (10 ng/mL), limit of quantification (25 ng/mL) and robustness. 3-Methylquercetin, luteolin, quercetin, 3,5-dihydroxy-6,7,8-trimethoxyflavone, apigenin and gnaphaliin A were present at relatively high levels in most of the samples analyzed. The samples of P. oxyphyllum and P. liebmannii showed the highest content of the 9 compounds analyzed. Whereas the samples of the 5 species of Gnaphalium showed the lowest levels, including non-detectable, of the 9 compounds quantified. This marks an important difference with Pseudognaphalium species. Furthermore, using UHPLC-ESI-QToF data with targeted and non-targeted approaches, 57 compounds, were identified in Mexican gordolobo samples. Flavonoids were the main group of compounds found in Mexican gordolobo.

Advances in extraction and purification of citrus flavonoids

Flavonoids are the representative active substances of citrus with various biological activities and high nutritional value. In order to evaluate and utilize citrus flavonoids, isolation and purification are necessary steps. This manuscript reviewed the research advances in the extraction and purification of citrus flavonoids. The structure classification, the plant and nutritional functions, and the biosynthesis of citrus flavonoids were summarized. The characteristics of citrus flavonoids and the selection of separation strategies were explained. The technical system of extraction and purification of citrus flavonoids was systematically described. Finally, outlook and research directions were proposed.

The Chemistry and the Anti-Inflammatory Activity of Polymethoxyflavonoids from Citrus Genus

Polymethoxyflavonoids (PMFs) are a large group of compounds belonging to the more general class of flavonoids that possess a flavan carbon framework decorated with a variable number of methoxy groups. Hydroxylated polymethoxyflavonoids (HPMFs), instead, are characterized by the presence of both hydroxyl and methoxy groups in their structural unities. Some of these compounds are the aglycone part in a glycoside structure in which the glycosidic linkage can involve the -OH at various positions. These compounds are particular to Citrus genus plants, especially in fruits, and they are present mainly in the peel. A considerable number of PMFs and HPMFs have shown promising biological activities and they are considered to be important nutraceuticals, responsible for some of the known beneficial effects on health associated with a regular consumption of Citrus fruits. Among their several actions on human health, it is notable that the relevant contribution in controlling the intracellular redox imbalance is associated with the inflammation processes. In this work, we aim to describe the status concerning the chemical identification and the anti-inflammatory activity of both PMFs and HPMFs. In particular, all of the chemical entities unambiguously identified by isolation and complete NMR analysis, and for which a biochemical evaluation on the pure compound was performed, are included in this paper.

Rapid profiling of potential antitumor polymethoxylated flavonoids in natural products by integrating cell biospecific extraction with neutral loss/diagnostic ion filtering-based high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry

INTRODUCTION

Citri Reticulatae Pericarpium Viride (CRPV, Qing Pi in Chinese) has been widely used in traditional Chinese medicine. Polymethoxylated flavonoids (PMFs), which are a special group of flavonoids with strong antitumor activity, are broadly distributed in citrus peels. However, systematic investigation of antitumor PMFs in CRPV has received little attention to date.

OBJECTIVES

An MCF-7 cell biospecific extraction method integrated with neutral loss/diagnostic ion filtering-based HPLC-QTOF-MS/MS strategy was developed for rapid and specific profiling of antitumor PMFs and systematic identification of PMFs in CRPV.

METHODOLOGY

By incubating MCF-7 cells with CRPV extract, potential antitumor PMFs specifically bound to cells and were isolated. Then, by systematic investigation of fragmentation pathways, neutral loss and diagnostic ion filtering strategies were proposed to comprehensively and accurately identify PMFs.

RESULTS

Sixteen antitumor PMFs were unambiguously or tentatively identified. Among them, minor compound 15 (5-hydroxy-6,7,8,3',4'-pentamethoxyflavone with a free hydroxyl group at C-5) exhibited excellent antitumor activity, with an IC₅₀ value of 2.81 ± 0.76 μg/mL, which is lower than that of 5-fluorouracil (IC₅₀ , 4.92 ± 0.83 μg/mL). Nobiletin (12) and tangeretin (16), two major PMFs, presented moderate antitumor activities with IC₅₀ values of 13.06 ± 1.85 and 17.07 ± 1.18 μg/mL, respectively, and their contents were sensitively and precisely determined.

CONCLUSIONS

To the best of our knowledge, this is the first report on the systematic investigation of antitumor PMFs in CRPV. The study will lay a foundation for the quality control and clinical application of CRPV.

Determination of Bioactive Components in Mandarin Fruits: A Review

During the last decade, there has been a continuous rise in the consumption of fresh easy-to-peel mandarins. However, the majority of the knowledge comes from other citrus fruit, like orange, while there are relatively few studies about mandarins and no comprehensive research on literature data about them. One of the most important steps in the analytical process is sample preparation. Its value is evident in analyzing the samples with complex matrices, such as in mandarin fruit. In addition, mandarin contains hundreds to thousands of various compounds and metabolites, some of them present in extremely low concentrations, that interfere with the detection of one another. Hence, mandarin samples are commonly pretreated by extraction to facilitate analysis of bioactive compounds, improve accuracy and quantification levels. There is an abundance of extraction techniques available, depending on the group of compounds of interest. Finally, modern analytical techniques, have been applied to cope with numerous bioactive compounds in mandarins. Considering all the above, this review aims to (i) list the most valuable procedures of sample preparation, (ii) highlight the most important techniques for extraction of bioactive compounds from mandarin fruit, and (iii) summarize current trends in the identification and determination of bioactive compounds in mandarin.

Neutral loss scan in complement with high-resolution MS/MS: Combination of detection methods for flavonoid and limonoid glycosides analysis

In this study, neutral loss scan and high-resolution MS/MS were used in combination to detect and tentatively identify various flavonoid and limonoid glycosides in navel orange albedo, juice, peel and pulp. These compound classes are of research interest due to their flavour and bioactive properties, and although flavonoid glycosides have been previously studied in other food matrices, to the best of our knowledge, neutral loss scans have not been used for the elucidation of limonoid glycosides. Neutral loss masses of 120, 162 and 308 Da were selected for the detection of hexose, rutinose and neohesperidose-substituted flavonoids, whereas 197 Da was explored for limonoid glycosides due to their tendency to form ammonium adducts. Fragmentation patterns obtained from targeted MS/MS were then used to differentiate rutinose and neohesperidose substituents as well as flavonoid subclasses of flavones, flavanones and flavonols. Additionally, high-resolution MS/MS was also used for the identification of aglycones by accurate mass (to four decimal places), allowing for the differentiation of aglycones with similar unit masses but different chemical formulas. In total, 19 flavonoid glycosides and six limonoid glycosides were detected. This workflow allows for a rapid screening of flavonoid and limonoid glycosides in citrus, which can be further extended to other food products such as tea.

Characterization of two closely related citrus cultivars using UPLC-ESI-MS/MS-based widely targeted metabolomics

Citrus cultivars are widely spread worldwide, and some of them only differ by specific mutations along the genome. It is difficult to distinguish them by traditional morphological identification. To accurately identify such similar cultivars, the subtle differences between them must be detected. In this study, UPLC-ESI-MS/MS-based widely targeted metabolomics analysis was conducted to study the chemical differences between two closely related citrus cultivars, Citrus reticulata 'DHP' and C. reticulata 'BZH'. Totally 352 metabolites including 11 terpenoids, 35 alkaloids, 80 phenolic acids, 25 coumarins, 7 lignans, 184 flavonoids and 10 other compounds were detected and identified; Among them, 15 metabolites are unique to DHP and 16 metabolites are unique to BZH. Hierarchical cluster analysis (HCA), principal component analysis (PCA), and orthogonal signal correction and partial least squares-discriminant analysis (OPLS-DA) can be used to clearly discriminate between DHP and BZH. 93 metabolites including 36 down-regulated and 57 up-regulated are significantly different in DHP and BZH. They are mainly involved in the biosynthesis of flavonoids, flavones, flavonols, and isoflavonoids. In addition, the relative content levels of flavonoids, alkaloids, and terpenoids are much higher in the peel of DHP than that of BZH, the presence of which may correlate with the quality difference of the peels. The results reported herein indicate that metabolite analysis based on UPLC-ESI-MS/MS is an effective means of identifying cultivars with different genotypes, especially those that cannot be distinguished based on traditional identification methods.

A review of chemical constituents and health-promoting effects of citrus peels

Citrus is one of the main fruits processed worldwide, producing a lot of industrial by-products. As the main part of citrus "residue", citrus peels have a wide application prospect. They could not only be directly used to produce various food products, but also be used as promising biofuels to produce ethanol and methane. Additionally, functional components (flavonoids, limonoids, alkaloids, essential oils and pectin) extracted from citrus peels have been related to the improvement of human health against active oxygen, inflammatory, cancer and metabolic disorders. Therefore, it is clear that the citrus peels have great potential to be developed into useful functional foods, medicines and biofuels. This review systematically summarizes the recent advances in current uses, processing, bioactive components and biological properties of citrus peels. A better understanding of citrus peels may provide reference for making full use of it.

Characteristics of Metabolites by Seed-Specific Inhibition of FAD2 in Brassica napus L

Fatty acid desaturase-2 (FAD2) is a key enzyme in the production of polyunsaturated fatty acids in plants. RNAi technology can reduce the expression of FAD2 genes in Brassica napus seeds and acquire transgenic B. napus plants with a high oleic acid content, but the effect of seed-specific inhibition of FAD2 expression on B. napus seed metabolites is not clear. Here we use widely targeted metabolomics to investigate the metabolites of normal-oleic-acid rapeseed (OA) and high-oleic-acid rapeseed (HOA) seeds, resulting in a total of 726 metabolites being detected. Among them, 24 differential metabolites were significantly downregulated and 88 differential metabolites were significantly upregulated in HOA rapeseed. In further lipid profile experiments, more lipids in B. napus seeds were accurately quantified. The contents of glycolipids and phospholipids that contain C18:1 increased significantly and C18:2 decreased because FAD2 expression was inhibited. The changes in the expression of key genes in related pathways were also consistent with the changes in metabolites. The insertion site of the ihpRNA plant expression vector was reconfirmed through genomewide resequencing, and the transgenic event did not change the sequence of FAD2 genes. There was no significant difference in the germination rate and germination potential between OA and HOA rapeseed seeds because the seed-specific ihpRNA plant expression vector did not affect other stages of plant growth. This work provides a theoretical and practical guidance for subsequent molecular breeding of high OA B. napus.

Comprehensive characterization of the chemical constituents in Yiganmingmu oral liquid and the absorbed prototypes in cynomolgus monkey plasma after oral administration by UPLC-Q-TOF-MS based on the self built components database

BACKGROUND

Yiganmingmu oral liquid (YGMM), a well known over-the-counter (OTC) drug in China, is composed of 12 types of valuable herbal medicines and has been widely used in clinical for the treatment of soreness and weakness of waist and knees, dizziness, memory loss, and fatigue. However, the chemical compositions of YGMM and its absorbed compounds in plasma remain unclear.

METHODS

Since chemical investigation is the first important step to reveal effects and action mechanisms of traditional Chinese medicine (TCM), in this study, based on the self built components database, systematic characterization of the chemical profile of YGMM in vitro was carried out by using a reliable UPLC-Q-TOF-MS method. Moreover, to obtain better understanding of the absorbed prototypes in plasma, serum pharmacochemistry analysis of YGMM after oral administration was conducted by using cynomolgus monkeys as animal model.

RESULTS

A total of 667 constituents from the 12 single herbal medicines were collected in the self built components database by searching the reported literatures, and 415 of them were initially screened as candidate compounds in YGMM by comparison of their experimental accurate mass measurements with those theoretical values. After that, 117 compounds including 17 phenolic acids, 25 flavonoids, 4 alkaloids, 10 phthalides, 5 monoterpenes, 8 triterpenoid saponins, 9 anthraquinones, and 39 other compounds, were unambiguously identified or tentatively characterized by analysing their MS/MS fragmentation patterns, and also by comparison with reference standards and those data reported in the literatures. 61 prototypes absorbed in plasma of cynomolgus monkey, including 13 phenolic acids, 21 flavonoids, 8 phthalides, 3 monoterpenes, 4 triterpenoid saponins, and 12 other compounds were tentatively assigned by serum pharmacochemistry analysis after oral administration.

CONCLUSION

It was the first comprehensive analysis of chemical constituents of YGMM and prototypes in plasma, and the data analysis strategy developed in this study showed high efficiency in the structural elucidations. The results might provide scientific evidence for further research on material basis of YGMM.

Characterization and identification of the major flavonoids in Phyllostachys edulis leaf extract by UPLC–QTOF–MS/MS

Phyllostachys edulis (PES), the most important bamboo species in China, is widely distributed in East Asia. Flavonoids, which are important bioactive natural compounds, often have similar structures, making their structural elucidation difficult. The aim of this study was to represent valuable, reliable mass spectral data for the identification of flavonoids in plant leaves. Ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC–Q-TOF-MS/MS) method was established for characterization and identification of the major flavonoids in PES leaf extract. A total of 13 flavonoids were simultaneously characterized, and their proposed characteristic product ions and fragmentation pathways were investigated. Thirteen compounds were separated on an Agilent Zorbax RRHD SB-C18 column (150 mm × 2.1 mm, 1.8 μm). On the basis of comparing with the 4 reference standards and the literature data, the other 9 flavonoids were identified by tandem mass spectrometry (MS/MS). Eight compounds (compounds 1, 4, 5, 8, 9, 10, 11, and 12) were found in PES leaves for the first time. An efficient UPLC–QTOF-MS/MS method was successfully applied for the structural identification of flavonoids in PES leaves. These results have practical applications for the rapid identification and structural characterization of these compounds in crude bioactive extracts or mixtures.

Supercritical CO2 Fluid Extraction for the Identification of Compounds from Citrus reticulata Semen by Ultra-High-Performance Liquid Chromatography Combined with Q-Exactive Orbitrap Tandem Mass Spectrometry

A rapid and simple method based on the coupling of supercritical fluid extraction and ultra-high-performance liquid chromatography combined with Q-Exactive Orbitrap tandem mass spectrometry (SFE-UHPLC-Q-Exactive Orbitrap-MS) detection for the identification of compounds from Citrus reticulata semen (CRS) was developed for the first time in this study. Through the optimization of the SFE parameters including extractive pressure, extractive temperature, and time, most of the compounds were successfully extracted at 50 °C, 33 MPa, and 2 h without an entraining agent, among which 32 compounds were successfully identified. Moreover, the operating conditions of UHPLC-Q-Exactive Orbitrap-MS were also optimized for the analysis of the SFE extracts, and the extracts in the CRS showed good separation performance in 20 min. A total of 28 compounds from the SFE extract were identified by comparing the standard sample together with full scan and related literature data, among which esters and flavonoids were the major compounds identified in the CRS extracts. In addition, 2 phenols, 2 aldehydes, 2 triterpenes, and 5 other compounds were identified. The SFE-UHPLC-Q-Exactive Orbitrap-MS method was successfully validated and applied for the identification of compounds from the CRS.

Analysis of Flavonoid Metabolites in Citrus Peels (Citrus reticulata "Dahongpao") Using UPLC-ESI-MS/MS

Flavonoids are a kind of essential substance for the human body because of their antioxidant properties and extremely high medicinal value. Citrus reticulata “Dahongpao” (DHP) is a special citrus variety that is rich in flavonoids, however little is known about its systematic flavonoids profile. In the present study, the presence of flavonoids in five important citrus varieties, including DHP, Citrus grandis Tomentosa (HZY), Citrus ichangensis Swingle (YCC), Citrus sinensis (L.) Osbeck (TC), and Citrus reticulata ‘Buzhihuo’ (BZH), was determined using a UPLC-ESI-MS/MS-based, widely targeted metabolome. Results showed that a total of 254 flavonoid metabolites (including 147 flavone, 39 flavonol, 21 flavanone, 24 anthocyanins, 8 isoflavone, and 15 polyphenol) were identified. The total flavonoid content of peels from DHP was the highest. DHP could be clearly separated from other samples through clustering analysis and principal component analysis (PCA). Further, 169 different flavonoid metabolites were observed between DHP peels and the other four citrus peels, and 26 down-regulated differential metabolites displayed important biological activities in DHP. At the same time, a unique flavonoid component, tricin 4′-O-syringyl alcohol, was only found in DHP, which could be used as a marker to distinguish between other varieties. This work might facilitate a better understanding of flavonoid metabolites between DHP peels and the other four citrus peels and provide a reference for its sufficient utilization in the future.

Chemical profiling of Banxia-Baizhu-Tianma decoction by ultra-fast liquid chromatography with tandem mass spectrometry

Banxia-Baizhu-Tianma decoction (BBTD) is a compound formulae of traditional Chinese medicine (TCM), which has been clinically used for treatments of neural vertigo, hypertension and epilepsy with a long history. In this study, with an ultra-fast liquid chromatography coupled with quadrupole time of flight mass spectrometry (UFLC-Q-TOF-MS) method, a total of 88 components in BBTD were identified by the accurate masses and fragmentation pathways including 19 flavonoids, 8 lactones, 12 triterpenoids, 10 phenolics, 14 amino acids, 13 nucleobases and nucleosides, 7 organic acids, and 5 other compounds. In addition, under the same chromatographic conditions, we developed an ultra-fast liquid chromatography coupled with quadrupole linear ion trap mass spectrometry (UFLC-Q-TRAP-MS) method to simultaneously quantify 20 bioactive components in multiple-reaction monitoring (MRM) mode. The assay method was validated in terms of linearity, precision, repeatability, recovery and was successfully applied for determination of 12 batches of BBTD. We hope that this study work would help to reveal the chemical profiling and provide a valuable and reliable approach for quality evaluation and even efficacy material basis study of BBTD.

Effect of Post-Harvest LED and UV Light Irradiation on the Accumulation of Flavonoids and Limonoids in the Segments of Newhall Navel Oranges (Citrus sinensis Osbeck)

To investigate the effect of post-harvest light irradiation on the accumulation of flavonoids and limonoids, harvested Newhall navel oranges were continuously exposed to light-emitting diode (LED) and ultraviolet (UV) light irradiation for 6 days, and the composition and content of flavonoids and limonoids in the segments were determined using UPLC-qTOF-MS at 0, 6, and 15 days after harvest. In total, six polymethoxylated flavonoids (PMFs), five flavone-O/C-glycosides, seven flavanone-O-glycosides, and three limonoids were identified in the segments. The accumulation of these components was altered by light irradiation. Red and blue light resulted in higher levels of PMFs during exposure periods. The accumulation of PMFs was also significantly induced after white light, UVB and UVC irradiation were removed. Red and UVC irradiation induced the accumulation of flavone and flavanone glycosides throughout the entire experimental period. Single light induced limonoid accumulation during exposure periods, but limonoid levels decreased significantly when irradiation was removed. Principal component analysis showed a clear correlation between PMFs and white light, between flavonoid glycosides and red light and UVC, and between limonoids and UVC. These results suggest that the accumulation of flavonoids and limonoids in citrus is regulated by light irradiation. White light, red light and UVC irradiation might be a good potential method for improving the nutrition and flavor quality of post-harvest citrus.

Analysis of phytochemical contributors to antioxidant capacity of the peel of Chinese mandarin and orange varieties

The phytochemicals in the peel of six oranges and ten mandarins including seven wild varieties and three cultivars were systematically characterised using UHPLC-Q-TOF-MS, and the correlation analysis was performed between phytochemicals and antioxidant capacity in order to investigate the phytochemical contributors to antioxidant capacity. The gradient elution was completed within 16 min and 92 compounds were undoubtedly or tentatively identified. Furthermore, the antioxidant capacities were determined using ABTS, DPPH and FRAP methods. The number of compounds, their contents and the antioxidant capacities were sequenced in the same order of the wild mandarins > cultivated mandarins > oranges. The correlation analysis that showed five compounds were significantly correlated with the antioxidant capacity and can act as main contributors to the citrus varieties with high antioxidant capacities. This study is systematic for the metabolites identification of mandarins and oranges and provides valuable information for effective utilisation of citrus peel and their bioactive compounds.