Biosynthesis of citrus flavonoids and their health effects

A multifunctional true caffeoyl coenzyme A O-methyltransferase enzyme participates in the biosynthesis of polymethoxylated flavones in citrus

Polymethoxylated flavones (PMFs) have received extensive attention due to their abundant bioactivities. Citrus peels specifically accumulate abundant PMFs, and methylation modification is a key step in PMF biosynthesis; however, the function of reported O-methyltransferase (OMT) in citrus is insufficient to elucidate the complete methylation process of PMFs. In this study, we analyzed the accumulation pattern of PMFs in the flavedo of the sweet orange (Citrus sinensis) cultivar "Bingtangcheng" at different developmental stages. We found that accumulation of PMFs was completed at the early stage of fruit development (60-d after flowering). Furthermore, we characterized a true caffeoyl-CoA O-methyltransferase (named CsCCoAOMT1) from C. sinensis. Functional analysis in vitro showed that CsCCoAOMT1 preferred flavonoids to caffeoyl-CoA and esculetin. This enzyme efficiently methylated the 6-, 7- 8-, and 3'-OH of a wide array of flavonoids with vicinal hydroxyl groups with a strong preference for quercetin (flavonol) and flavones. The transient overexpression and virus-induced gene silencing experiments verified that CsCCoAOMT1 could promote the accumulation of PMFs in citrus. These results reveal the function of true CCoAOMTs and indicate that CsCCoAOMT1 is a highly efficient multifunctional O-methyltransferase involved in the biosynthesis of PMFs in citrus.

Dietary sinensetin and polymethoxyflavonoids: Bioavailability and potential metabolic syndrome-related bioactivity

Sinensetin is among the most ubiquitous polyphenols in citrus fruit and recently has been extensively studied for its ability to prevent or treat diseases. The current literature on the bioavailability of sinensetin and its derivatives was reviewed and the potential ameliorative effects of metabolic syndrome in humans were evaluated. Sinensetin and its derivatives mainly aggregated in the large intestine and extensively metabolized through gut microbiota (GM) and the liver. So intestinal microorganisms had a significant influence on the absorption and metabolism of sinensetin. Interestingly, not only GM acted on sinensetin to metabolize them, but sinensetin also regulated the composition of GM. Thus, sinensetin was metabolized as methyl, glucuronide and sulfate metabolites in the blood and urine. Furthermore, sinensetin was reported to have the beneficial effect of ameliorating metabolic syndromes, including disorders of lipid metabolism (obesity, NAFLD, atherosclerosis), glucose metabolism disorder (insulin resistant) and inflammation, in terms of improving the composition of intestinal flora and modulating metabolic pathway factors in relevant tissues. The present work strongly elucidated the potential mechanism of sinensetin in improving metabolic disorders and supported the contribution of sinensetin to health benefits, thus offering a better perspective in understanding the role played by sinensetin in human health.

Comparative transcriptome and metabolome analysis identifies a citrus ERF transcription factor CsERF003 as flavonoid activator

Transcription factor (TF) modulation is a promising strategy for plant flavonoid improvement. Here, we observed evident decreases in some major flavones and flavonols and the expression of some key related genes in a 'Newhall' navel orange mutant (MT) relative to the wild type (WT). A consistently downregulated ERF TF CsERF003 in MT could increase the contents of major flavonoids and the precursor phenylalanine when transiently overexpressed in citrus fruit. Overexpression of CsERF003 in 'Micro-Tom' tomato (OE) resulted in a darker and redder fruit color than wild type 'Micro-Tom' (WTm). Two major flavonoids, naringeninchalcone and kaempferolrutinoside, were averagely induced by 7.99- and 36.83-fold in OEs, respectively, while little change was observed in other polyphenols, such as caffeic acid, ferulic acid, and gallic acid. Key genes involved in the initiation of phenylpropanoid (PAL, 4CH, and 4CL) and flavonoid (CHS and CHI) biosynthesis were up-regulated, while most genes participating in the biosynthesis of other polyphenols, such as HCT and CCR, were down-regulated in OEs. Therefore, it could be concluded that carbon flux floods into the phenylpropanoid biosynthetic pathway and is then specifically directed for flavonoid biosynthesis. CsERF003 may be a potentially promising gene for fruit quality improvement and engineering of natural flavonoid components.

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.

Influence of Different Rootstocks on Fruit Quality and Primary and Secondary Metabolites Content of Blood Oranges Cultivars

Blood oranges have high concentrations of bioactive compounds that are beneficial to health. In Europe, the cultivation of blood oranges is increasing due to their excellent nutritional properties. In Citrus crops, rootstocks play an important role in juice and can increase the content of bioactive compounds. The morphological, qualitative and nutritional parameters were analyzed in cultivars 'Tarocco Ippolito', 'Tarocco Lempso', 'Tarocco Tapi' and 'Tarocco Fondaconuovo' grafted onto Citrus macrophylla and Citrus reshni. 'Tarocco Lempso' grafted onto Citrus macrophylla obtained the highest values of weight (275.78 g), caliber (81.37 mm and 76.79 mm) and juice content (162.11 g). 'Tarocco Tapi' grafted onto Citrus reshni obtained the most interesting qualitative parameters (15.40 °Brix; 12.0 MI). 'Tarocco Lempso' grafted onto Citrus reshni obtained the most intense red juice (a* = 9.61). Overall, the highest concentrations of primary metabolites were in proline, aspartate, citric acid, and sucrose. The results showed that 'Tarocco Ippolito' juice grafted onto Citrus reshni had the highest levels of total hydroxycinnamic acids (263.33 mg L^-1), total flavones (449.74 mg L^-1) and total anthocyanins (650.42 mg L^-1). To conclude, 'Tarocco Lempso' grafted onto Citrus macrophylla obtained the best values of agronomic parameters, and the cultivars grafted onto Citrus reshni obtained significantly higher concentrations in primary and secondary metabolites.

Comparative study on secondary metabolites from different citrus varieties in the production area of Zhejiang

To investigate the distribution pattern of bioactive components and their correlations between citrus varieties, we thoroughly analyzed secondary metabolites (including flavonoids, phenolic acids, carotenoids, and limonoids) in the peel and pulp of 11 citrus varieties from the production area of Zhejiang. Citrus peels accumulated metabolites far more than the pulp, and the accumulation varied significantly between species. Flavonoids were the most abundant compounds, followed by phenolic acids, with carotenoids and limonoids being far less abundant than the first two, but limonoids were more abundant than carotenoids. Hesperidin was the main flavonoid in most varieties, but cocktail grapefruit and Changshanhuyou contained naringin, with Ponkan having the most abundant polymethoxylated flavones (PMFs). The major components of phenolic acids, carotenoids, and limonoids were ferulic acid, β-cryptoxanthin, and limonin, respectively. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) indicated that these components were mostly correlated with each other, and these citrus varieties could be categorized into four groups by pulp and three groups by peel. The obtained results filled the data gap for secondary metabolites from local citrus and could provide data references for citrus resource utilization, selection and breeding of superior varieties, and other research.

Advances in the study of the function and mechanism of the action of flavonoids in plants under environmental stresses

MAIN CONCLUSION

This review summarizes the anti-stress effects of flavonoids in plants and highlights its role in the regulation of polar auxin transport and free radical scavenging mechanism. As secondary metabolites widely present in plants, flavonoids play a vital function in plant growth, but also in resistance to stresses. This review introduces the classification, structure and synthetic pathways of flavonoids. The effects of flavonoids in plant stress resistance were enumerated, and the mechanism of flavonoids in plant stress resistance was discussed in detail. It is clarified that plants under stress accumulate flavonoids by regulating the expression of flavonoid synthase genes. It was also determined that the synthesized flavonoids are transported in plants through three pathways: membrane transport proteins, vesicles, and bound to glutathione S-transferase (GST). At the same time, the paper explores that flavonoids regulate polar auxin transport (PAT) by acting on the auxin export carrier PIN-FORMED (PIN) in the form of ATP-binding cassette subfamily B/P-glycoprotein (ABCB/PGP) transporter, which can help plants to respond in a more dominant form to stress. We have demonstrated that the number and location of hydroxyl groups in the structure of flavonoids can determine their free radical scavenging ability and also elucidated the mechanism by which flavonoids exert free radical removal in cells. We also identified flavonoids as signaling molecules to promote rhizobial nodulation and colonization of arbuscular mycorrhizal fungi (AMF) to enhance plant-microbial symbiosis in defense to stresses. Given all this knowledge, we can foresee that the in-depth study of flavonoids will be an essential way to reveal plant tolerance and enhance plant stress resistance.

A review of citrus plants as functional foods and dietary supplements for human health, with an emphasis on meta-analyses, clinical trials, and their chemical composition

Fruits, flowers, leaves, essential oils, hydrosols, and juices of citrus spp. Are utilized to prepare various forms of food products. Along with their nutritional values, in the health industry, different parts of the plants of the citrus genus have been used as supplements or remedies to prevent or control diseases. This review focused on reported meta-analyses and clinical trials on the health benefits of citrus plants as functional foods. Also, chemical compounds of various citrus species were reviewed. The following information sources were used for data collection: Google Scholar, the Web of Science, Scopus, and PubMed. Various keywords, including "citrus AND chemical compounds," "citrus AND phytochemicals," "citrus species," "citrus AND meta-analysis," "nutritional and therapeutical values of citrus spp.," "clinical trials AND citrus," "clinical trials AND Rutaceae," "health benefits of citrus spp.," "citrus edible or non-edible applications," and scientific names of the citrus plants were utilized to collect data for the review. The scientific name and common name of all twenty-eight citrus species, along with any of the above keywords, were also searched in the mentioned databases. Scientific papers and data sources were sought to review and discuss the citrus plant's nutritional and therapeutic importance. Several meta-analyses and clinical trials have reported beneficial effects of citrus spices on a variety of cancer risks, cardiovascular risk factors, neurologic disorders, urinary tract conditions, and gastrointestinal tract conditions. They have shown anxiolytic, antimicrobial, and pain-alleviating effects. Some of them can be helpful in managing obesity and cardiovascular risk factors.

Diosmetin alleviates benzo[a]pyrene-exacerbated H1N1 influenza virus-induced acute lung injury and dysregulation of inflammation through modulation of the PPAR-γ-NF-κB/P38 MAPK signaling axis

The severity of a viral respiratory illness was greatly exacerbated after exposure to a contaminant containing benzo[a]pyrene (B[a]P). Flavonoid-rich fruit intake has gained intense interest due to their health-promoting benefits for viral respiratory diseases, including influenza viruses. In our study, diosmetin (3',5,7-trihydroxy-4'-methoxyflavone), a naturally occurring hydroxylated methoxyflavone that is abundant in Citrus fruits, was explored for its effects on B[a]P-exacerbated H1N1 influenza virus-mediated inflammation and lung injury. Initially, in vivo results demonstrated that diosmetin protected against H1N1 virus-elicited acute lung injury. Simultaneously, H1N1 virus or B[a]P-stimulated A549 cells treated with diosmetin inhibited NF-κB and P-P38 activation, resulting in suppression of pro-inflammatory cytokines and apoptosis. Interestingly, diosmetin obviously promoted the expression of PPAR-γ as well as nuclear translocation of PPAR-γ, whereas, PPAR-γ inhibition by GW9662 weakened the inhibitory effects of diosmetin on H1N1 virus or B[a]P-mediated activation of NF-κB and P-P38, elevated expression of pro-inflammatory mediators as well as apoptosis. Furthermore, it was surprising to discover that mice exposed to both B[a]P and H1N1 viruses contributed to exacerbated acute lung injury, which were significantly ameliorated by diosmetin administration. In vitro studies showed that A549 cells with the combination of B[a]P and H1N1 virus augmented NF-κB and P-P38 activation, accompanied by higher levels of pro-inflammatory mediators and apoptosis, all of which were also significantly reduced by diosmetin treatment. Repressing PPAR-γ abrogated the inhibitory effects of diosmetin on B[a]P-exacerbated H1N1 virus-mediated NF-κB and P-P38 activation, inflammation, and apoptosis in A549 cells. Our findings suggest that diosmetin protected against B[a]P-exacerbated H1N1 virus-mediated lung injury by suppressing the exacerbation of NF-κB and P38 kinase activation in a PPAR-γ-dependent manner, suggesting potential benefits for B[a]P-exacerbated influenza-related illness therapeutics.

A Scientometric Study to a Critical Review on Promising Anticancer and Neuroprotective Compounds: Citrus Flavonoids

Flavonoids derived from citrus plants are favored by phytomedicinal researchers due to their wide range of biological activities, and relevant studies have been sustained for 67 years (since the first paper published in 1955). In terms of a scientometric and critical review, the scientometrics of related papers, chemical structures, and pharmacological action of citrus flavonoids were comprehensively summarized. The modern pharmacological effects of citrus flavonoids are primarily focused on their anticancer activities (such as breast cancer, gastric cancer, lung cancer, and liver cancer), neuroprotective effects (such as anti-Alzheimer’s disease, Parkinson’s disease), and metabolic diseases. Furthermore, the therapeutic mechanism of cancers (including inducing apoptosis, inhibiting cell proliferation, and inhibiting cancer metastasis), neuroprotective effects (including antioxidant and anti-inflammatory), and metabolic diseases (such as non-alcoholic fatty liver disease, type 2 diabetes mellitus) were summarized and discussed. We anticipate that this review could provide an essential reference for anti-cancer and neuroprotective research of citrus flavonoids and provide researchers with a comprehensive understanding of citrus flavonoids.

Integrated transcriptomic and metabolomic analyses reveal key genes controlling flavonoid biosynthesis in Citrus grandis 'Tomentosa' fruits

As a well-recognized traditional Chinese medicine (TCM), immature fruits of Citrus grandis 'Tomentosa' (CGT) serve to cure chronic cough in humans. Specialized metabolites including flavonoids may have contribute to this curing effect. Knowledge about the molecular mechanisms underlying flavonoid biosynthesis in 'Tomentosa' fruits will, therefore, support the breeding of varieties with improved medicinal properties. Hence, we profiled the transcriptomes and metabolites of the fruits of two contrasting C. grandis varieties, namely 'Zheng-Mao' ('ZM') used in TCM production, and a locally cultivated pomelo, namely 'Guang-Qing' ('GQ'), at four developmental stages. A total of 39 flavonoids, including 14 flavanone/flavone, 5 isoflavonoids, 12 flavonols, and 6 anthocyanins, were identified, and 16 of which were quantitatively determined in the fruits of the two varieties. We found that 'ZM' fruits contain more flavonoids than 'GQ'. Specifically, rhoifolin levels were significantly higher in 'ZM' than in 'GQ'. We annotated 31,510 genes, including 1,387 previously unknown ones, via transcriptome sequencing of 'ZM' and 'GQ.' A total of 646 genes were found to be differentially expressed between 'ZM' and 'GQ' throughout at all four fruit developmental stages, indicating that they are robust expression markers for future breeding programs. Weighted gene co-expression network analysis identified 18 modules. Combined transcriptional and metabolic analysis revealed 25 genes related to flavonoid biosynthesis and 16 transcriptional regulators (MYBs, bHLHs, WD40) that may be involved in the flavonoids biosynthesis in C. grandis 'Tomentosa' fruits.

Naringenin and Hesperidin as Promising Alternatives for Prevention and Co-Adjuvant Therapy for Breast Cancer

Citrus (genus Citrus L.) fruits are essential sources of bioactive compounds with antioxidant properties, such as flavonoids. These polyphenolic compounds are divided into subclasses, in which flavanones are the most prominent. Among them, naringenin and hesperidin are emerging compounds with anticancer potential, especially for breast cancer (BC). Several mechanisms have been proposed, including the modulation of epigenetics, estrogen signaling, induction of cell death via regulation of apoptotic signaling pathways, and inhibition of tumor invasion and metastasis. However, this information is sparse in the literature and needs to be brought together to provide an overview of how naringenin and hesperidin can serve as therapeutic tools for drug development and as a successful co-adjuvant strategy against BC. This review detailed such mechanisms in this context and highlighted how naringenin and hesperidin could interfere in BC carcinogenesis and be helpful as potential alternative therapeutic sources for breast cancer treatment.

Evaluation of Possible Neobavaisoflavone Chemosensitizing Properties towards Doxorubicin and Etoposide in SW1783 Anaplastic Astrocytoma Cells

Flavonoids exert many beneficial properties, such as anticancer activity. They were found to have chemopreventive effects hindering carcinogenesis, and also being able to affect processes important for cancer cell pathophysiology inhibiting its growth or promoting cell death. There are also reports on the chemosensitizing properties of flavonoids, which indicate that they could be used as a support of anticancer therapy. It gives promise for a novel therapeutic approach in tumors characterized by ineffective treatment, such as high-grade gliomas. The research was conducted on the in vitro culture of human SW1783 anaplastic astrocytoma cells incubated with neobavaisoflavone (NEO), doxorubicin, etoposide, and their combinations with NEO. The analyses involved the WST-1 cell viability assay and image cytometry techniques including cell count assay, Annexin V assay, the evaluation of mitochondrial membrane potential, and the cell-cycle phase distribution. We found that NEO affects the activity of doxorubicin and etoposide by reducing the viability of SW1783 cells. The combination of NEO and etoposide caused an increase in the apoptotic and low mitochondrial membrane potential subpopulations of SW1783 cells. Changes in the cell cycle were observed in all combined treatments. These findings indicate a potential chemosensitizing effect exerted by NEO.

The variability of phenolic constituents and antioxidant properties among wild populations of Ziziphora clinopodioides Lam

In this study, phenolic derivatives and antioxidant activities of fourteen Ziziphora clinopodioides populations, as well as LC-MS/MS analysis of three specific flavonoids were evaluated. Generally, high contents of phenolic derivatives were found in shoot extracts compared to roots. LC-MS/MS, a powerful analytical technique, was employed for the identification and quantify the individual flavonoids in Z. clinopodioides populations' extracts, in a quantity order of quercetin > rutin > apigenin. Scavenging activity by DPPH and FRAP was performed, and accordingly, in the shoot, the highest values for the DDPH were 4.61 ± 0.4 and 7.59 ± 0.26 µg ml- 1 in populations 1 and 13, respectively, and for the FRAP were 328.61 ± 5.54 and 292.84 ± 2.85 mg g DW- 1, in populations 6 and 1 respectively. Multivariate analysis results of the principal component analysis indicated the amount of polyphenols to be useful indicators in differentiating the geographical localities which explain 92.7% of the total variance. According to the results of hierarchical cluster analysis, the studied populations could be separated into two groups in that the contents of phenolic derivatives and antioxidant activities of different plant parts. Both shoot and root samples were well discriminated with the orthogonal partial least squares discriminant analysis (R2X: 0.861; Q2: 0.47) model. The validity of the model was confirmed by using receiver operating characteristic curve analysis and permutation tests. Such data make an important addition to our current knowledge of Ziziphora chemistry and are decisive in the identification of germplasms with a homogeneous phytochemical profile, high chemical content and bioactivity. The present results could also be helpful for the potential application of Z. clinopodioides in different kinds of industries as natural antioxidants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01283-y.

Identification and Analysis of Metabolites That Contribute to the Formation of Distinctive Flavour Components of Laoxianghuang

In addition to volatile compounds, metabolites also have a great effect on the flavour of food. Fresh finger citron cannot be eaten directly because of its spicy and bitter taste, so it is made into a preserved fruit product known as Laoxianghuang (LXH). To investigate the metabolites that have an effect on the flavour of LXH, untargeted metabolomics was performed using an ultrahigh-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS), and the metabolites of the Laoxianghuang samples from different locations in the Chaoshan area were compared and analysed. A total of 756 metabolites were identified and distinct differences were revealed among the different Laoxianghuang samples. A total of 33 differential metabolites with the most significant changes were screened through further multivariate analytical steps, and each group of samples had unique metabolites. For instance, pomolic acid had the highest content in the JG sample, while L-glycyl-L-isoleucine was rich in the QS sample. Moreover, flavonoid metabolites made the greatest contribution to the unique flavour of Laoxianghuang. The metabolic pathways involved are the biosynthetic pathways of flavonoids, isoflavonoids, flavones, and flavonols. This study can provide some creative information for distinguishing the quality differences of Laoxianghuang from the perspective of metabolites and offer preliminary theoretical support to characterise the formation of flavour substances in Laoxianghuang.

Comprehensive Review of Recent Advances in Chiral A-Ring Flavonoid Containing Compounds: Structure, Bioactivities, and Synthesis

Flavonoids are a group of natural polyphenolic substances that are abundant in vegetables, fruits, grains, and tea. Chiral A-ring-containing flavonoids are an important group of natural flavonoid derivatives applicable in a wide range of biological activities such as, cytotoxic, anti-inflammatory, anti-microbial, antioxidant, and enzyme inhibition. The desirable development of chiral A-ring-containing flavonoids by isolation, semi-synthesis or total synthesis in a short duration proves their great value in medicinal chemistry research. In this review, the research progress of chiral A-ring-containing flavonoids, including isolation and extraction, structural identification, pharmacological activities, and synthetic methods, is comprehensively and systematically summarized. Furthermore, we provide suggestions for future research on the synthesis and biomedical applications of flavonoids.

Recent developments in citrus bioflavonoid encapsulation to reinforce controlled antioxidant delivery and generate therapeutic uses: Review

Citrus fruits contain numerous antioxidative biomolecules including phenolic acids, flavonols, flavanones, polymethoxyflavones (PMFs), and their derivatives. Previous in vitro and in vivo studies thoroughly investigated the antioxidant and therapeutic potential of bioflavonoids extracted from different citrus varieties and fruit fractions. Major bioflavonoids such as hesperidin, naringin, naringenin, and PMFs, had restricted their incorporation into food and health products due to their poor solubility, chemical stability and bioavailability. Considering these limitations, modern encapsulation methodologies such as hydrogelation, liposomal interactions, emulsifications, and nanoparticles have been designed to shield bioflavonoids with improved target distribution for therapeutic enhancements. The size, durability, and binding efficiency of bioflavonoid-loaded encapsulates were acquired by the optimized chemical and instrumental parameters such as solubility, gelation, dispersion, extrusion, and drying. Bioflavonoid-enriched encapsulates have been also proven to be effective against cancer, inflammation, neurodegeneration, and various other illnesses. However, in the future, newer natural binding agents with higher binding capacity might accelerate the encapsulating potential, controlled release, and enhanced bioavailability of citrus bioflavonoids. Overall, these modern encapsulation systems are currently leading to a new era of diet-based medicine, as demand for citrus fruit-based nutritional supplements and edibles grows.

Polymethoxyflavones from citrus peel: advances in extraction methods, biological properties, and potential applications

Citrus peel, as an effective component of citrus by-products, contains a large number of natural active components, including pectin, vitamins, dietary fiber, essential oil, phenolic compounds, flavonoids, and so on. With the development of the circular economy, citrus peel has attracted extensive concern in the food industry. The exploitation of citrus peel would assist in excavating potential properties and alleviating the environmental burden. Polymethoxyflavones (PMFs) exist almost in citrus peel, which have remarkable biological activities including antioxidant, anti-inflammatory, anti-cancer, and anti-obesity. Therefore, PMFs from citrus peel have the potential to develop as dietary supplements in the near future. Collectively, it is essential to take action to optimize the extraction conditions of PMFs and make the most of the extracts. This review mainly compiles several extraction methods and bioactivities of PMFs from citrus peel and introduces different applications including food processing, pharmaceutical industry, and plant rhizosphere to develop better utilization of citrus PMFs.

Impact of diet on human nutrition, immune response, gut microbiome, and cognition in an isolated and confined mission environment

Long-duration spaceflight impacts human physiology, including well documented immune system dysregulation. The space food system has the potential to serve as a countermeasure to maladaptive physiological changes during spaceflight. However, the relationship between dietary requirements, the food system, and spaceflight adaptation requires further investigation to adequately define countermeasures and prioritize resources on future spaceflight missions. We evaluated the impact of an enhanced spaceflight diet, with increased quantity and variety of fruits, vegetables, fish, and other foods rich in flavonoids and omega-3 fatty acids, compared to a standard spaceflight diet on multiple health and performance outcomes in 16 subjects over four 45-day closed chamber missions in the NASA Human Exploration Research Analog (HERA). Subjects consuming the enhanced spaceflight diet had lower cholesterol levels, lower stress (i.e. cortisol levels), better cognitive speed, accuracy, and attention, and a more stable microbiome and metatranscriptome than subjects consuming the standard diet. Although no substantial changes were observed in the immune response, there were also no immune challenges, such as illness or infection, so the full benefits of the diet may not have been apparent in these analog missions. These results indicate that a spaceflight diet rich in fruits, vegetables, and omega-3 fatty acids produces significant health and performance benefits even over short durations. Further investigation is required to fully develop dietary countermeasures to physiological decrements observed during spaceflight. These results will have implications for food resource prioritization on spaceflight missions.

Metabolomics and proteomics reveal the molecular basis of colour formation in the pericarp of Chinese wild rice (Zizania latifolia)

Chinese wild rice (Zizania latifolia) is rich in flavonoids and the characteristic colour of its pericarp is attributed to the flavonoids. In this study, the molecular basis of the colour change in the pericarp of Chinese wild rice was studied using metabolomics and proteomics. Whole seeds in three developmental stages (10, 20, and 30 days after flowering) were characterised based on phenolic contents, free amino acids (FAAs), and the expression level and activities of enzymes critical in flavonoid biosynthesis. The total phenolic and proanthocyanidin contents of Chinese wild rice increased gradually, whereas total flavonoid and FAA contents decreased during seed development. Metabolomic analysis revealed gradual upward trends for 57 flavonoids (sub classes 1, 3, and 10) related to colour change in the pericarp. Proteomic analysis showed that the phenylpropanoid biosynthesis metabolic pathway was enriched with differentially expressed proteins and was associated with flavonoid biosynthesis. Proteomic data suggested that leucoanthocyanidin reductase and WD40 repeat protein may be involved in flavonoid biosynthesis in Chinese wild rice, which was also verified by real-time quantitative PCR. Our results provide new insights into the understanding of the colour formation in the pericarp of Chinese wild rice.

Comparative transcriptomic and metabolomic analyses reveal the delaying effect of naringin on postharvest decay in citrus fruit

INTRODUCTION

Naringin exhibits antioxidant capacity and can partially inhibit pathogens in many horticultural products, such as citrus fruit; however, the effects of naringin on the storage quality and mechanisms that regulate senescence in citrus fruit have not been comprehensively analyzed.

METHODS AND RESULTS

In this study, exogenous naringin treatment was found to significantly delay citrus fruit disease, decreasing the H₂O₂ content, increasing the antioxidant capacity and maintaining the quality of the fruit. Metabolomic analysis of citrus peel indicated the vast majority (325) of metabolites belonging to flavonoids. Moreover, the auraptene, butin, naringenin, and luteolin derivative levels within the phenylpropanoid pathway were significantly higher in the naringin-treated fruit than in the control fruit. Transcriptomic analysis also revealed that twelve genes in the phenylpropanoid and flavonoid biosynthesis pathways were significantly upregulated. Further analysis with a co-expression network revealed significant correlation between these differential genes and metabolites. Additionally, MYC and WRKY, screened from the MAPK signaling pathway, may contribute to naringin-induced disease resistance.

CONCLUSION

In conclusion, naringin treatment can efficiently delay decay and maintain the quality of citrus fruit, mainly by promoting metabolites accumulation, and upregulating differentially expressed genes in phenylpropanoid and flavonoid biosynthesis pathway. This study provides a better understanding of the regulatory mechanisms through which naringin delays citrus fruit decay and maintains fruit quality.

Integrated Analysis of Metabolome and Transcriptome Reveals the Difference in Flavonoid Biosynthesis between the Red- and White-Sarcocarp Pomelo Fruits

Flavonoids are bioactive secondary metabolites that play multiple roles in plants. However, studies on the flavonoid accumulation of the pomelo fruit are rare. In this study, we conducted a widely targeted metabolome analysis by using ultra-performance liquid chromatography and tandem mass spectrometry and identified 550 metabolites in the sarcocarp from red (C. maxima Merr. var. Tubtim Siam) and white pomelos (C. maxima (Burm.) Osbeck). A total of 263 significantly changed metabolites were detected from the 550 metabolites. Content analysis of the significantly changed metabolites (SCMs) showed that 138 SCMs were highly accumulated, whereas 125 SCMs were observed with lower content in red-sarcocarp pomelo. Importantly, 103 of the 263 SCMs were flavonoids, including 34 flavonoids, 29 flavonols, 18 flavonoid carbonosides, 9 dihydroflavones, 6 isoflavones, 5 anthocyanins, 1 dihydroflavonol, and 1 chalcone. Gene ontology analysis indicated that upregulated genes in red-sarcocarp pomelo were significantly enriched in GO terms related to flavonoids including flavonoid biosynthetic processes. Several important differentially expressed genes were detected in the correlation network, especially Cg2g009540 which is an orthologous gene of AtCHS, also detected in flavonoid biosynthesis networks, and which could be related to the high level of total flavonoids in the red-sarcocarp pomelo. Our study demonstrated the fluctuation of flavonoid biosynthesis in the two pomelo cultivars and laid a theoretical foundation for pomelo breeding to generate fruits with a high flavonoid content.

Metabolic Profiling and Antioxidant Analysis for the Juvenile Red Fading Leaves of Sweetpotato

Leaves of sweetpotato (Ipomoea batatas L.) are promising healthy leafy vegetable. Juvenile red fading (JRF) leaves of sweetpotato, with anthocyanins in young leaves, are good candidates for developing functional vegetables. Here, metabolic profiling and possible antioxidants were analyzed for five leaf stages of the sweetpotato cultivar "Chuanshan Zi". The contents of anthocyanins, total phenolics, and flavonoids all declined during leaf maturation, corresponding to declining antioxidant activities. By widely targeted metabolomics, we characterized 449 metabolites belonging to 23 classes. A total of 193 secondary metabolites were identified, including 82 simple phenols, 85 flavonoids, 18 alkaloids, and eight terpenes. Analysis of the metabolic data indicates that the antioxidant capacity of sweetpotato leaves is the combined result of anthocyanins and many other colorless compounds. Increased levels of "chlorogenic acid methyl ester", a compromised form of chlorogenic acid, significantly correlated with the declined antioxidant abilities. Besides anthocyanins, some significant metabolites contributing to the high antioxidant property of the sweetpotato leaves were highlighted, including chlorogenic acids, isorhamnetin glycosides, trans-4-hydroxycinnamic acid methyl ester, 4-methoxycinnamic acid, esculetin, caffeate, and trigonelline. This study provides metabolic data for the utilization of sweetpotato leaves as food sources, and sheds light on the metabolomic change for JRF leaves of other plants.

Multiomics analysis of the mechanisms behind flavonoid differences between purple and green tender shoots of Camellia sinensis var. assamica

Flavonoids are rich in tea plants (Camellia sinensis), and responsible for the flavor and healthful benefits of tea beverage. The anthocyanin levels in the purple tender shoots are higher than in the general green leaves of tea plant, which provide special materials to search metabolic mechanisms of flavonoid enrichment in plant. In this work, flavonoid differences between purple and green shoots from tea cultivars "Zijuan" (ZJ) and "Yunkang10" (YK-10) were investigated through metabolomic analysis, and mechanisms for their difference were surveyed by comparative transcriptomic and proteomic analysis. Levels of 34 flavonoids were different between ZJ and YK-10 shoots. Among them, 8 and 6 were marker metabolites in ZJ and YK-10, respectively. The differentially expressed genes (DEGs), differentially expressed proteins (DEPs), and different-level metabolites (DLMs) between ZJ and YK-10 were researched, respectively; and interactions including DEG-DLM, DEP-DLM, DEG-DEP, and DEG-DEP-DLM were analyzed; the contents of 18 characteristic flavonoids in tea leaves and expressions of 34 flavonoid metabolic genes were measured to verify the omics results. Integrated above analyses, a proposed model of flavonoids biosynthesis in tea shoots were established. The differential expression of the leucoanthocyanidin reductase (LAR), anthocyanidin synthase (ANS), anthocyanidin reductase (ANR), UDPG-flavonoid glucosyltransferase (UGT) 75L12 and 94P1 at gene level, and the ANS, ANR, and UGT78A15 at protein level, were closely associated with differences in flavonoids between ZJ and YK-10 shoot. Together, this study provides new information on the flavonoid accumulation mechanism in tea plant.

Bioactive Compounds, Nutritional Quality and Antioxidant Capacity of the Red-Fleshed Kirkwood Navel and Ruby Valencia Oranges

Kirkwood Navel and Ruby Valencia are two spontaneous bud-mutations of the ordinary Washington Navel and Valencia late oranges characterized by the red coloration of their flesh. The purpose of this study was to analyze the physiological features, internal fruit quality, contents of relevant bioactive compounds and antioxidant capacity in the pulps of the red-fleshed fruits compared with the ordinary oranges during late development and maturation. In general, the content of sugars, organic acids, vitamin C, tocopherols, total phenolics and flavonoids, the hydrophilic antioxidant capacity and their changes during maturation were similar in the red-fleshed oranges and in the corresponding blond oranges. However, the mature Ruby fruits contained lower concentrations of sugars, malic and succinic acid and higher levels of citric acid than the ordinary Valencia. The major difference between the pulps of the Kirkwood and Ruby oranges and those of the ordinary oranges was the higher lipophilic antioxidant capacity and SOAC (singlet oxygen absorption capacity) of the former. Together, the high and unique content and composition of carotenoids in Kirkwood and Ruby may contribute to an enhanced antioxidant capacity without any detrimental effects on other fruit-quality attributes, making these varieties good sources of phytochemicals for the fresh-fruit and juice-processing citrus industries.

Integrated metabolomics and transcriptomics insights on flavonoid biosynthesis of a medicinal functional forage, Agriophyllum squarrosum (L.), based on a common garden trial covering six ecotypes

Agriophyllum squarrosum (L.) Moq., well known as sandrice, is an important wild forage in sandy areas and a promising edible and medicinal resource plant with great domestication potential. Previous studies showed flavonoids are one of the most abundant medicinal ingredients in sandrice, whereby isorhamnetin and isorhamnetin-3-glycoside were the top two flavonols with multiple health benefits. However, the molecular regulatory mechanisms of flavonoids in sandrice remain largely unclear. Based on a common garden trial, in this study, an integrated transcriptomic and flavonoids-targeted metabolomic analysis was performed on the vegetative and reproductive periods of six sandrice ecotypes, whose original habitats covered a variety of environmental factor gradients. Multiple linear stepwise regression analysis unveiled that flavonoid accumulation in sandrice was positively correlated with temperature and UVB and negatively affected by precipitation and sunshine duration, respectively. Weighted co-expression network analysis (WGCNA) indicated the bHLH and MYB transcription factor (TF) families might play key roles in sandrice flavonoid biosynthesis regulation. A total of 22,778 differentially expressed genes (DEGs) were identified between ecotype DL and ecotype AEX, the two extremes in most environmental factors, whereby 85 DEGs could be related to known flavonoid biosynthesis pathway. A sandrice flavonoid biosynthesis network embracing the detected 23 flavonoids in this research was constructed. Gene families Plant flavonoid O-methyltransferase (AsPFOMT) and UDP-glucuronosyltransferase (AsUGT78D2) were identified and characterized on the transcriptional level and believed to be synthases of isorhamnetin and isorhamnetin-3-glycoside in sandrice, respectively. A trade-off between biosynthesis of rutin and isorhamnetin was found in the DL ecotype, which might be due to the metabolic flux redirection when facing environmental changes. This research provides valuable information for understanding flavonoid biosynthesis in sandrice at the molecular level and laid the foundation for precise development and utilization of this functional resource forage.

Selenium content and nutritional quality of Brassica chinensis L enhanced by selenium engineered nanomaterials: The role of surface charge

Selenium engineered nanomaterials (Se ENMs)-enabled agriculture has developed rapidly, however, the roles of surface charge in the bioavailability and enrichment efficiency of Se ENMs are still unknown. Herein, various Se ENMs of homogenous size (40-60 nm) and different surface charges (3.2 ± 0.7, -29.0 ± 0.4, and 45.5 ± 1.3 mV) were prepared to explore the Se content and nutritional quality in Brassica chinensis L. The results demonstrated that soil application of various Se ENMs (0.05 mg kg^-1) displayed different bio-availabilities via modulating the secretion of root exudates (e.g., tartaric, malic, and citric acids), microbial community composition (e.g., Flavobacterium, Pseudomonas, Paracoccus, Bacillus and Rhizobium) and root cell wall. Negatively charged Se ENMs (Se (-)) showed the highest Se content in the shoot of B. chinensis (3.7-folds). Se (-) also significantly increased yield (156.9%) and improved nutritional quality (e.g., ascorbic acid, amino acids, flavonoids, fatty acids, and tricarboxylic acid) of B. chinensis. Moreover, after harvest, the Se (-) did not lead to significant change in Se residue in soil, but the amount of Se residue in soil was increased by 5.5% after applying the traditional Se fertilizer (selenite). Therefore, this study provides useful information for producing Se-fortified agricultural products, while minimizing environmental risk.

Integrating transcriptome and chemical analyses to reveal the anti-Alzheimer's disease components in Verbena officinalis Linn

Verbena officinalis Linn. is a kind of traditional Chinese medicine, which has a long history of application and shows good effects on neuroprotection. Therefore, we consider that V. officinalis may be a potential drug for treating Alzheimer's disease (AD). First, ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) pointed out that the main chemical components in V. officinalis were iridoid glycosides, phenylethanoid glycosides, and flavonoids. These compounds were used for molecular docking and the results showed that these compounds had good anti-AD activity. To explore the biosynthetic pathway of anti-AD components in V. officinalis, UPLC and ultraviolet (UV) spectrophotometry were used for contents determination and the result was leaf > stem > root. At the same time, 92,867 unigenes were annotated in V. officinalis transcriptome; 206, 229, 115 related unigenes were, respectively, annotated in iridoid glycoside, phenylethanoid glycoside, and flavonoid pathway, of which 61, 73, and 35 were differential expression genes. The components had relatively high expression in leaves, which was consistent with the quantitative results. In addition, the tissue distribution particularity of verbenalin may be related to the branching of pathways. Meanwhile transcription factors VoWRKY6 and VoWRKY7 may be involved in the regulation of iridoid glycoside biosynthesis. Further, VoWRKY3, VoWRKY9, and VoWRKY12 may be related to flavonoid biosynthesis. The above research is helpful to explore the biosynthetic pathway of anti-AD components and the regulation mechanism of active components and to further explore the anti-AD effect of V. officinalis.

Targeted Metabolomics With a Chemometric Study of Oxygenated Heterocyclic Aglycones as a Tool for Preliminary Authenticity Assessment of Orange and Grapefruit Juices

Profiles of citrus juice oxygenated heterocyclic aglycones (OHAs), which are notable marker secondary metabolites, were used to assess the authenticity of sweet orange and grapefruit juices in situations where mandarin and pomelo juices might be adulterants. Thirty-nine known OHAs, including 10 methoxyflavones, 13 coumarins, and 16 furanocoumarins, as well as 13 tentatively screened OHAs, were analyzed in orange, mandarin, grapefruit and pomelo juices using our newly developed high-resolution HPLC-UV and fluorescence detection method. Quantitative OHA profiles from 158 pure juice samples were obtained to establish a purity discriminant model using an omics strategy. Reduction of OHA variables showed that three important methoxyflavones, i.e. isosinensetin, tangeretin and sinensetin provided the best discrimination ability between sweet orange and mandarin juices. There are two subtypes of pomelos, Shatianyou Group and Wendan Group, of which juices should be separately compared to grapefruit juice. Five OHAs, namely meranzin, 3,5,6,7,8,3',4'-heptamethoxyflavone, osthole, 6',7'-epoxybergamottin, and bergamottin were found to discriminate Shatianyou Group of pomelo juice from grapefruit juice; whereas three OHAs, namely bergaptol, isomeranzin, and 6',7'-dihydroxybergamottin were able to discriminate Wendan Group of pomelo juice from grapefruit juice. The established partial least squares discriminant analysis (PLS-DA) models were capable of detecting as little as 10% mandarin juice in sweet orange juice and 10% pomelo juice in grapefruit juice, allowing for fast prescreening of excess addition with good reliability (root mean square error of prediction, RMSEP < 5%).

Neuroprotective Effects and Therapeutic Potential of the Citrus Flavonoid Hesperetin in Neurodegenerative Diseases

Neurodegenerative disorders affect more than fifty million Americans each year and represent serious health threats as the population ages. Neuroinflammation and oxidative stress are critical in the onset, progression, and pathogenesis of neurodegenerative diseases such as Alzheimer’s (AD), Parkinson’s (PD), and amyotrophic lateral sclerosis (ALS). A wide range of natural compounds has been investigated because of their antioxidant, anti-inflammatory, and neuroprotective properties. The citrus flavonoid hesperetin (HPT), an aglycone of hesperidin found in oranges, mandarins, and lemons, has been extensively reported to exert neuroprotective effects in experimental models of neurogenerative diseases. This review has compiled multiple studies on HPT in both in vivo and in vitro models to study neurodegeneration. We focused on the modulatory effects of hesperetin on the release of cellular anti-inflammatory and antioxidative stress mediators. Additionally, this review discusses the hesperetin effect in maintaining the levels of microRNA (miRNA) and modulating autophagy as it relates to hesperetin’s protective mechanisms against neurodegeneration. Moreover, this review is focused on providing experimental data for hesperetin’s potential as a neuroprotective compound and discusses reported evidence that HPT crosses the blood–brain barrier. In summary, this review shows the evidence available in the literature to indicate the efficacy of hesperetin in delaying the onset of neurodegenerative diseases.

Citrus Peel Flavonoid Extracts: Health-Beneficial Bioactivities and Regulation of Intestinal Microecology in vitro

Citrus peel and its extracts are rich in flavonoids, which are beneficial to human health. In this study, the extraction, component analysis, biological activity and intestinal microbiota regulation of citrus peel flavonoid extracts (CPFEs) were investigated. CPFEs from 14 Chinese cultivars were purified by ultrasound-assisted extraction and XAD-16 macroporous resin. The total flavonoid content of lemon was greatest at 103.48 ± 0.68 mg/g dry weight (DW) by NaNO2-Al(NO3)3-NaOH spectrophotometry. Using high-performance liquid chromatography–diode array detection, the highest concentrations of naringin, hesperidin and eriocitrin were found in grapefruit (52.03 ± 0.51 mg/g DW), chachiensis (43.02 ± 0.37 mg/g DW) and lemon (27.72 ± 0.47 mg/g DW), respectively. Nobiletin was the most polymethoxylflavone in chachiensis at 16.91 ± 0.14 mg/g DW. CPFEs from chachiensis and grapefruit had better antioxidant activity, α-glucosidase inhibitory and sodium glycocholate binding ability. In addition, chachiensis and grapefruit CPFEs had positive effects on intestinal microecology, as evidenced by a significant increase in the relative abundance of Bifidobacterium spp., and production of short-chain fatty acids, especially acetic acid, by a simulated human intestinal model. Collectively, our results highlight the biological function of CPFEs as prebiotic agents, indicating their potential use in food and biomedical applications.

Comparative Analysis of the Chalcone-Flavanone Isomerase Genes in Six Citrus Species and Their Expression Analysis in Sweet Orange (Citrus sinensis)

Citrus fruit contains rich nutrients which is edible and of officinal value. Citrus flavanones are widely used in the treatment of cardiovascular and other diseases, and they are a foundational material of Chinese medicine. The chalcone-flavanone isomerase (CHI) plays a key role in flavanone synthesis. Therefore, we comprehensively analyzed CHI genes in Citrus species. Here, thirty CHI genes were identified for the first time in six Citrus species, which were divided into CHI and FAP groups. Evolutionary analysis showed that CHI gene members were highly conserved and were an ancient family. All CsCHI genes showed the highest expression level after the second physiological fruit-falling period in C. sinensis. CsCHI1 and CsCHI3 were highly expressed at 50 days after the flowering (DAF) stage in albedo. The expression of CsFAP2 and CsCHI3 genes at the 50 DAF stage was 16.5 and 24.3 times higher than that at the 220 DAF stage, respectively. The expression of CsCHI1, CsCHI3, and CsFAP2 genes in the peel was higher than that in the pulp, especially in common sweet orange. The CsCHI3 gene maintained a high expression level in the epicarp and juice sac at all periods. The members of CHIs interacted with chalcone synthase (CHS), flavonol synthase/flavanone 3-hydroxylase (FLS) and naringenin, and 2-oxoglutarate 3-dioxygenase (F3H) to form heterodimers, which might together play a regulatory role and participate in the flavonoid pathway. This study will provide the basis for the selection of flavonoids in plant tissues and periods and fundamental information for further functional studies.

Compendium of naringenin: potential sources, analytical aspects, chemistry, nutraceutical potentials and pharmacological profile

Naringenin is flavorless, water insoluble active principle belonging to flavanone subclass. It exhibits a diverse pharmacological profile as well as divine nutraceutical values. Although several researchers have explored this phytoconstituent to evaluate its promising properties, still it has not gained recognition at therapeutic levels and more clinical investigations are still required. Also the neutraceutical potential has limited marketed formulations. This compilation includes the description of reported therapeutic potentials of naringenin in variety of pathological conditions alongwith the underlying mechanisms. Details of various analytical investigations carried on this molecule have been provided along with brief description of chemistry and structural activity relationship. In the end, various patents filed and clinical trial data has been provided. Naringenin has revealed promising pharmacological activities including cardiovascular diseases, neuroprotection, anti-diabetic, anticancer, antimicrobial, antiviral, antioxidant, anti-inflammatory and anti-platelet activity. It has been marketed in the form of nanoformulations, co-crystals, solid dispersions, tablets, capsules and inclusion complexes. It is also available in various herbal formulations as nutraceutical supplement. There are some pharmacokinetic issue with naringenin like poor absorption and low dissolution rate. Although these issues have been sorted out upto certain extent still further research to investigate the bioavailability of naringenin from herbal supplements and its clinical efficacy is essential.

UHPLC-Q-TOF-MS/MS-based Metabolite Profiling of Ganpu Tea in Rat Urine and Feces

Ganpu tea is a novel type of beverage produced from Pu-erh tea stuffed in the pericarp of Citrus reticulata “Chachi”. It has gained considerable popularity in China owing to its inviting flavor and health effects. However, the in vivo metabolites of Ganpu tea, which may contribute to its overall health effects, are still unclear. In the present work, rat urine and feces samples were collected after oral administration of Ganpu tea extract (GTE), and then subjected to ultra-high-performance liquid chromatography/quadrupole-time-of-flight tandem mass spectrometry (UHPLC-Q-TOF-MS/MS)-based metabolite profiling. As a result, 27 prototype compounds and 41 metabolites derived from caffeic acid, gallic acid, p-coumaric acid, xanthine, catechin, polymethoxyflavone, (PMF) flavanone, and flavone were identified in rat urine and feces. Based on the detected metabolites, the ingested prototype compounds derived from Ganpu tea were found to undergo extensive phase II metabolism in rats, especially and sulfation. These results will be valuable for interpreting the health effects of Ganpu tea.

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.

Bioactive Compounds of Citrus Fruits: A Review of Composition and Health Benefits of Carotenoids, Flavonoids, Limonoids, and Terpenes

The increased consumption of fruits, vegetables, and whole grains contributes to the reduced risk of many diseases related to metabolic syndrome, including neurodegenerative diseases, cardiovascular disease (CVD), diabetes, and cancer. Citrus, the genus Citrus L., is one of the most important fruit crops, rich in carotenoids, flavonoids, terpenes, limonoids, and many other bioactive compounds of nutritional and nutraceutical value. Moreover, polymethoxylated flavones (PMFs), a unique class of bioactive flavonoids, abundantly occur in citrus fruits. In addition, citrus essential oil, rich in limonoids and terpenes, is an economically important product due to its potent antioxidant, antimicrobial, and flavoring properties. Mechanistic, observational, and intervention studies have demonstrated the health benefits of citrus bioactives in minimizing the risk of metabolic syndrome. This review provides a comprehensive view of the composition of carotenoids, flavonoids, terpenes, and limonoids of citrus fruits and their associated health benefits.

Phytogenic Selenium Nanoparticles Elicited the Physiological, Biochemical, and Antioxidant Defense System Amelioration of Huanglongbing-Infected ‘Kinnow’ Mandarin Plants

Citrus greening or huanglongbing (HLB) is commonly known as yellow dragon disease and affects citrus production worldwide. Therefore, it has a significant impact on and deleterious effects in the agro-industrial sector. Significant efforts have been made to combat this disease and mitigate its destructive impact on citrus production, but still, there is no effective biocompatible treatment available to control HLB disorder. This study is considered the first biocompatible approach to evaluate the potential of phytogenic selenium nanoparticles (SeNPs) to improve the health of HLB-infected ‘Kinnow’ mandarin plants. Polymerase chain reactions (PCRs) with specific primers were used to detect HLB disease in ‘Kinnow’ mandarin plants, and PCR products were sequenced to identify Candidatus Liberibacter asiaticus (CLas), and accession numbers for CLas1 and CLas2, MZ851933 and MZ851934, respectively, were obtained. SeNPs were synthesized by using Allium sativum L. clove extract as a reducing, capping, and stabilizing agent and various techniques such as UV-visible spectrophotometry, energy dispersive X-rays, scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were used to confirm the biogenesis of SeNPs. Different concentrations of SeNPs (25, 50, 75, and 100 mg L⁻¹) were exogenously applied to HLB-infected ‘Kinnow’ mandarin plants and obtained spectacular results. The obtained results from the current study proved that 75 mg L⁻¹ of SeNPs was most effective to improve the chlorophyll, carotenoids, relative water content (RWC), membrane stability index (MSI), total soluble sugar (TSS), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), total flavonoid content (TFC), and total phenolic content (TPC) and significant decrease was observed in hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and proline (PRO) contents of HLB-infected ‘Kinnow’ mandarin plants as compared to untreated diseased citrus plants. In conclusion, these results allow us to synthesize the SeNPs formulation as a promising management strategy to treat the HLB disease in citrus plants.

Functional Characterization of a Flavone Synthase That Participates in a Kumquat Flavone Metabolon

Flavones predominantly accumulate as O- and C-glycosides in kumquat plants. Two catalytic mechanisms of flavone synthase II (FNSII) support the biosynthesis of glycosyl flavones, one involving flavanone 2-hydroxylase (which generates 2-hydroxyflavanones for C-glycosylation) and another involving the direct catalysis of flavanones to flavones for O-glycosylation. However, FNSII has not yet been characterized in kumquats. In this study, we identified two kumquat FNSII genes (FcFNSII-1 and FcFNSII-2), based on transcriptome and bioinformatics analysis. Data from in vivo and in vitro assays showed that FcFNSII-2 directly synthesized apigenin and acacetin from naringenin and isosakuranetin, respectively, whereas FcFNSII-1 showed no detectable catalytic activities with flavanones. In agreement, transient overexpression of FcFNSII-2 in kumquat peels significantly enhanced the transcription of structural genes of the flavonoid-biosynthesis pathway and the accumulation of several O-glycosyl flavones. Moreover, studying the subcellular localizations of FcFNSII-1 and FcFNSII-2 demonstrated that N-terminal membrane-spanning domains were necessary to ensure endoplasmic reticulum localization and anchoring. Protein-protein interaction analyses, using the split-ubiquitin yeast two-hybrid system and bimolecular fluorescence-complementation assays, revealed that FcFNSII-2 interacted with chalcone synthase 1, chalcone synthase 2, and chalcone isomerase-like proteins. The results provide strong evidence that FcFNSII-2 serves as a nucleation site for an O-glycosyl flavone metabolon that channels flavanones for O-glycosyl flavone biosynthesis in kumquat fruits. They have implications for guiding genetic engineering efforts aimed at enhancing the composition of bioactive flavonoids in kumquat fruits.

Integrated Transcriptomics and Widely Targeted Metabolomics Analyses Provide Insights Into Flavonoid Biosynthesis in the Rhizomes of Golden Buckwheat (Fagopyrum cymosum)

Golden buckwheat (Fagopyrum cymosum) is used in Traditional Chinese Medicine. It has received attention because of the high value of its various medicinal and nutritional metabolites, especially flavonoids (catechin and epicatechin). However, the metabolites and their encoding genes in golden buckwheat have not yet been identified in the global landscape. This study performed transcriptomics and widely targeted metabolomics analyses for the first time on rhizomes of golden buckwheat. As a result, 10,191 differentially expressed genes (DEGs) and 297 differentially regulated metabolites (DRMs) were identified, among which the flavonoid biosynthesis pathway was enriched in both transcriptome and metabolome. The integration analyses of the transcriptome and the metabolome revealed a network related to catechin, in which four metabolites and 14 genes interacted with each other. Subsequently, an SG5 R2R3-MYB transcription factor, named FcMYB1, was identified as a transcriptional activator in catechin biosynthesis, as it was positively correlated to eight flavonoid biosynthesis genes in their expression patterns and was directly bound to the promoters of FcLAR2 and FcF3'H1 by yeast one hybrid analysis. Finally, a flavonoid biosynthesis pathway was proposed in the rhizomes of golden buckwheat, including 13 metabolites, 11 genes encoding 9 enzymes, and 1 MYB transcription factor. The expression of 12 DEGs were validated by qRT-PCR, resulting in a good agreement with the Pearson R ranging from 0.83 to 1. The study provided a comprehensive flavonoid biosynthesis and regulatory network of golden buckwheat.

Beneficial Role of Fruits, Their Juices, and Freeze-Dried Powders on Inflammatory Bowel Disease and Related Dysbiosis

Inflammatory bowel disease (IBD) is a group of complex chronic inflammatory conditions affecting the gastrointestinal tract. It is linked to a number of genetic and environmental factors able to perturb the immune-microbiome axis. Diet is the most investigated variable both for its role in the etiology of IBD and for its beneficial potential in the treatment of the symptoms. Dietary products may influence intestinal inflammation through different mechanisms of action, such as the modulation of inflammatory mediators, the alteration of gene expression, changes in gut permeability, and modifications in enteric flora composition. A consisting number of studies deal with the link between nutrition and microbial community, and particular attention is paid to plant-based foods. The effects of the dietary intake of different fruits have been investigated so far. This review aims to present the most recent studies concerning the beneficial potential of fruit consumption on human gut microbiota. Investigated plant species are described, and obtained results are presented and discussed in order to provide an overview of both in vitro and in vivo effects of fruits, their juices, and freeze-dried powders.

The Potential Role of Phytonutrients Flavonoids Influencing Gut Microbiota in the Prophylaxis and Treatment of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), characterized by the chronic inflammation of the gastrointestinal tract, is comprised of two idiopathic chronic intestinal inflammatory diseases. As the incidence of IBD increases, so does the need for safe and effective treatments. Trillions of microorganisms are colonized in the mammalian intestine, coevolve with the host in a symbiotic relationship. Gut microbiota has been reported to be involved in the pathophysiology of IBD. In this regard, phytonutrients flavonoids have received increasing attention for their anti-oxidant and anti-inflammatory activities. In this review, we address recent advances in the interactions among flavonoids, gut microbiota, and IBD. Moreover, their possible potential mechanisms of action in IBD have been discussed. We conclude that there is a complex interaction between flavonoids and gut microbiota. It is expected that flavonoids can change or reshape the gut microbiota to provide important considerations for developing treatments for IBD.