Identification of phenolic compounds from a unique citrus species, finger lime (Citrus australasica) and their inhibition of LPS-induced NO-releasing in BV-2 cell line

The phytochemical composition and unexplored potential of Australian native plants for application in physical activity-related muscle recovery and inflammation: a literature review

Native plants are adaptable in various environmental conditions in part through the production of unique phytochemicals which may have beneficial effects on human health. Native Australian fruits contain higher phytochemical and antioxidant levels than most Western fruits, suggesting potential for greater health benefits arising from their consumption. These beneficial effects, in turn, may be mediated by the inhibition of inflammatory pathways as well as oxidative stress via the regulation of reactive oxygen (ROS) and/or nitrogen (RNS) species levels. Unaccustomed or strenuous exercise causes muscle damage and soreness, that may be driven by increased ROS and inflammation. There is growing interest in the application of polyphenol-rich food supplementation for the alleviation of exercise-induced oxidative stress, for the reduction of exercise-induced inflammation and improvement of muscle recovery. Therefore, the aim of this review was to provide an overview of the phytochemical and bioactive composition of some Australian native plant foods and their potential use for functional food development in the management of muscle recovery and inflammation. Native plant foods and food products could be beneficial for reducing inflammation, though it is important to note that most of the research in this field has been conducted in animal models or in vitro, in addition to there being little data on skeletal muscle inflammation. Further studies, particularly in humans, would be needed to confirm these effects and to determine the appropriate dosages and forms of native foods and food products for consumption to reduce inflammation and enhance muscle recovery.

Anion exchanger1 (AE1/SLC4A1) function is impaired in red blood cells from prediabetic subjects: Potential benefits of finger lime (Citrus australasica, Faustrime cultivar) juice extract

Prediabetes is a risk state that defines a high chance of developing diabetes and cardiovascular disease. Oxidative stress mediated by hyperglycemia-induced production of reactive species could play a crucial role in this context. In the present study, we investigated whether the anion exchange capability mediated by AE1 (SLC4A1), which is sensitive to oxidative stress, was altered in human red blood cells (RBCs) obtained from prediabetic volunteers. In addition, we assessed the precise composition of bioactive compounds and the potential benefits of finger lime juice extract (Citrus australasica, Faustrime cultivar) in counteracting oxidative stress-related functional alterations. Human RBCs from normal and prediabetic volunteers were incubated with 50 µg/mL juice extract for 2 h at 25°C. Juice extract restored alterations of the anion exchange capability mediated by AE1 and prevented the structural rearrangements of AE1 and α/β-spectrin in prediabetic RBCs. AE1 functional and structural alterations were not associated with an increase in lipid peroxidation or protein oxidation at the level of the plasma membrane. An increased production of intracellular ROS, which provoked the oxidation of hemoglobin to methemoglobin, both reverted by juice extract, was instead observed. Importantly, juice extract also induced a reduction in glycated hemoglobin levels in prediabetic RBCs. Finally, juice extract blunted the overactivation of the endogenous antioxidant enzymes catalase and superoxide dismutase and prevented glutathione depletion in prediabetic RBCs. These findings contribute to clarifying cellular and molecular mechanisms related to oxidative stress and glycation events that may influence RBC and systemic homeostasis in prediabetes, identify AE1 as a sensitive biomarker of RBC structural and function alterations in prediabetes and propose finger lime juice extract as a natural antioxidant for the treatment and/or prevention of the complications associated with the prediabetic condition.

Citrus By-Products as a Valuable Source of Biologically Active Compounds with Promising Pharmaceutical, Biological and Biomedical Potential

Citrus fruits processing results in the generation of huge amounts of citrus by-products, mainly peels, pulp, membranes, and seeds. Although they represent a major concern from both economical and environmental aspects, it is very important to emphasize that these by-products contain a rich source of value-added bioactive compounds with a wide spectrum of applications in the food, cosmetic, and pharmaceutical industries. The primary aim of this review is to highlight the great potential of isolated phytochemicals and extracts of individual citrus by-products with bioactive properties (e.g., antitumor, antimicrobial, antiviral, antidiabetic, antioxidant, and other beneficial activities with health-promoting abilities) and their potential in pharmaceutical, biomedical, and biological applications. This review on citrus by-products contains the following parts: structural and chemical characteristics; the utilization of citrus by-products; bioactivities of the present waxes and carotenoids, essential oils, pectins, and phenolic compounds; and citrus by-product formulations with enhanced biocactivities. A summary of the recent developments in applying citrus by-products for the treatment of different diseases and the protection of human health is also provided, emphasizing innovative methods for bioaccessibility enhancements (e.g., extract/component encapsulation, synthesis of biomass-derived nanoparticles, nanocarriers, or biofilm preparation). Based on the representative phytochemical groups, an evaluation of the recent studies of the past six years (from 2018 to 2023) reporting specific biological and health-promoting activities of citrus-based by-products is also provided. Finally, this review discusses advanced and modern approaches in pharmaceutical/biological formulations and drug delivery (e.g., carbon precursors for the preparation of nanoparticles with promising antimicrobial activity, the production of fluorescent nanoparticles with potential application as antitumor agents, and in cellular imaging). The recent studies implementing nanotechnology in food science and biotechnology could bring about new insights into providing innovative solutions for new pharmaceutical and medical discoveries.

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.

LC-MS and GC-MS Data Fusion Metabolomics Profiling Coupled with Multivariate Analysis for the Discrimination of Different Parts of Faustrime Fruit and Evaluation of Their Antioxidant Activity

The comparative chemical composition of different part of Faustrime fruits (peels, pulp, albedo, and seeds) extracted with different solvents was determined by GC-MS and UHPLC-HRMS QTof. The obtained data were also combined for their in vitro antioxidant activity by multivariate analysis to define a complex fingerprint of the fruit. The principal component analysis model showed the significative occurrence of volatile organic compounds as α-bisabolol and α-trans-bergamotol in the pulp and albedo, hexanoic acid in the seeds, and several coumarins and phenolics in the peels. The higher radical scavenging activity of the pulp was related to the incidence of citric acid in partial least square regression.

Comparative Volatilomic Profile of Three Finger Lime (Citrus australasica) Cultivars Based on Chemometrics Analysis of HS-SPME/GC-MS Data

Finger lime is receiving growing attention as an ingredient of gastronomic preparations of haute cuisine for its delicious flavor and fragrance and for its appealing aspect. Volatile compounds play a crucial role in determining the organoleptic characteristics of the fruit and its pleasantness for consumers. The aim of the present study was to investigate the volatile profiles by headspace solid phase micro-extraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) in the peel and, for the first time, in the pulp of three Australian finger lime cultivars grown in Sicily (southern Italy): Pink Pearl, Sanguinea, and Faustrime, allowing to overall identify 84 volatile organic compounds (VOCs). The analytical data showed that the three cultivars were characterized by distinct volatile chemotypes: limonene/sabinene/bicyclogermacrene in the Pink Pearl, limonene/γ-terpinene/bicyclogermacrene in the Sanguinea, and limonene/β-phellandrene/γ-terpinene in the Faustrime. Moreover, some volatiles, found exclusively in one cultivar, could be considered potential markers of the individual cultivar. PCA allowed us to clearly discriminate the samples into three clusters: the first related to the Sanguinea peel, the second to the Faustrime peel, and a third group associated with the Pink Pearl peel along with the pulp of the three cultivars. Accordingly, the VOCs that mostly contributed to the differentiation of the three finger lime cultivars were also identified. Among them, D-limonene, sabinene γ-terpinene, α-pinene, α-phellandrene, β-myrcene, p-cymene, linalool, δ-elemene, ledene, bicyclogermacrene β-citronellol, α-bergamotene, α-caryophillene, and β-bisabolene, have been previously reported to exhibit important biological activities, suggesting that these cultivars, in addition to possessing unique volatile profiles, can show promise for several applications in pharmaceutical and food industry, namely for development of functional foods.

Comparing Metabolomic and Essential Oil Fingerprints of Citrus australasica F. Muell (Finger Lime) Varieties and Their In Vitro Antioxidant Activity

Comparative chemical analyses among peel and pulp essential oils (EOs) and methanolic extracts of four Citrus australasica varieties (Red, Collette, Pink Ice, and Yellow Sunshine), and the hybrid Faustrime, were performed using GC-MS and UHPLC-DAD-HR-Orbitrap/ESI-MS. Peel and pulp extracts were also analysed for their in vitro antioxidant activity on a Balb/3T3 clone A31 mouse embryo fibroblast cell line. The results of peel and pulp EOs were mainly characterised by monoterpenes and sesquiterpenes, respectively. All peels displayed a higher total phenol content (TPC) than pulps, and consequently a greater antioxidant activity. Collette peels and Pink Ice pulps showed the highest amount of identified flavonoids (e.g., luteolin, isosakuranetin, and poncirin derivatives). Collette and Red peels were rich in anthocyanins (delphinidin and petunidin glycosides), exhibiting the maximum protective activity against induced oxidative damage. In conclusion, finger lime fruits are good sources of health-promoting phytocomplexes, with the Red, Collette, and Pink Ice varieties being the most promising.

"Planeterranea": An attempt to broaden the beneficial effects of the Mediterranean diet worldwide

Non-communicable diseases (NCDs) lead to a dramatic burden on morbidity and mortality worldwide. Diet is a modifiable risk factor for NCDs, with Mediterranean Diet (MD) being one of the most effective dietary strategies to reduce diabetes, cardiovascular diseases, and cancer. Nevertheless, MD transferability to non-Mediterranean is challenging and requires a shared path between the scientific community and stakeholders. Therefore, the UNESCO Chair on Health Education and Sustainable Development is fostering a research project-"Planeterranea"-aiming to identify a healthy dietary pattern based on food products available in the different areas of the world with the nutritional properties of MD. This review aimed to collect information about eating habits and native crops in 5 macro-areas (North America, Latin America, Africa, Asia, and Australia). The information was used to develop specific "nutritional pyramids" based on the foods available in the macro-areas presenting the same nutritional properties and health benefits of MD.

Metabolomic Investigation of Citrus latifolia and the Putative Role of Coumarins in Resistance to Black Spot Disease

Citrus black spot (CBS) is a disease caused by the fungus Phyllosticta citricarpa that affects citrus plants, causing fruit blemish and premature drop that result in severe economic losses in commercial citrus orchards. However, CBS symptoms and effects may vary depending on the citrus species: Citrus limon (lemon) is susceptible and highly affected by the disease, while no CBS-related damage has ever been observed for Citrus latifolia (Tahiti lime), implying that it must be resistant to the disease. The difference in the response to this disease provided the opportunity to gain insight into the metabolites responsible for the resistance by comparison of the metabolomic profiles of these two citrus species. Metabolic variations of C. limon and C. latifolia inoculated with P. citricarpa were analyzed using various metabolomic-based platforms including 1H NMR for overall metabolic profiling, and LC-MS and HPTLC for targeted analysis. The 1H NMR spectra of the samples demonstrated that certain phenolics were strongly induced after pathogenic inoculation, especially in the resistant species. The induced phenolics were identified from C. latifolia by further 1H NMR, LCMS and HPTLC analysis yielding six prenylated and methoxy coumarins, i.e., 5,7-dimethoxycoumarin, 5-geranyloxy-7-methoxycoumarin, 7-geranyloxycoumarin, 8-methoxypsoralen, 5,8-dimethoxypsoralen and 5-geranyloxypsoralen. These isolated coumarins and a coumarin-rich fraction were tested against the fungal pathogen, P. citricarpa, to evaluate their activity. None of the individual coumarins exhibited a significant inhibition, while the coumarin fraction exhibited a strong antifungal activity suggesting a synergistic interaction of its components. To obtain further insight into the roles of these compounds in the plant defense, the possible mechanisms of the individual coumarins were tested using an in-silico model, the PASS Online Tool; the analysis showed that each coumarin appeared to have a unique defense mechanism, even with very slight variations in the chemical structures. The results could provide evidence of the existence of a complex plant defense mechanism consisting in a multitude of synergistic interactions between compounds.

Measurement of Naringin from Citrus Fruits by High-Performance Liquid Chromatography - a Review

Naringin is a flavonoid found primarily in citrus species with especially high concentrations being present in grapefruit (Citrus paradisi), bitter orange (Citrus aurantium), and pomelo (Citrus grandis). Because of its many positive effects on human health, naringin has been the focus of increasing attention in recent years. Recently, conventional extraction methods have been commonly replaced with unconventional methods, such as ultrasound-assisted extraction (UAE) and other, more eco-friendly extraction methods requiring little-to-no environmentally harmful solvents or significantly less energy. Naringin analysis is most commonly done via high-performance liquid chromatography (HPLC), and ultrahigh-performance liquid chromatography (UHPLC) coupled with a mass spectrometer (MS) or a photodiode array (DAD) detector. The aim of this review is to provide an overview of recent trends developments in the extraction, sample preparation, and liquid chromatographic analysis of the compound originating from citrus fruits or their products.

Cryptochlorogenic acid and its metabolites ameliorate myocardial hypertrophy through a HIF1α-related pathway

Cryptochlorogenic acid (4-CQA) is a phenolic acid that has antioxidant and anti-inflammatory activities. Our preliminary study found that 4-CQA has a good effect on isoproterenol (ISO)-induced myocardial hypertrophy, while the mechanism remains largely unknown. This study aimed at delineating the metabolites and metabolic pathways of 4-CQA using liquid mass spectrometry and molecular biotechnology, exploring possible active metabolites and the mechanism of myocardial hypertrophy amelioration in H9c2 cells, and finally, investigating the pharmacokinetics of 4-CQA and its active metabolites in vivo. In summary, 56 potential effective metabolites were distinguished in rat urine, feces, plasma samples and heart tissue after intragastric administration of 4-CQA, and the main metabolic reaction types of 4-CQA included hydrogenation, methylation, glucuronidation, sulfation, hydration and their composite reactions in in vivo biotransformation. Besides, 4-CQA and its main active metabolites, caffeic acid and 4-O-feruloylquinic acid, significantly ameliorated pathological cardiac hypertrophy of H9c2 cells treated with ISO based on the Akt/mTOR/HIF-1α pathway. In addition, this study demonstrated that the prototype drugs 4-CQA and 4-O-ferulylquinic acid generally exhibit similar pharmacokinetic characteristics and caffeic acid presents relatively late peak time and low peak concentration in rats, which make them suitable candidate drugs.

Comprehensive Characterization and Quantification of Antioxidant Compounds in Finger Lime (Citrus australasica L.) by HPLC-QTof-MS and UPLC-MS/MS

Australian finger limes (Citrus australasica L.), an unusual citrus due to its unique pulp with a caviar-like appearance, has reached the global market as a promising source of bioactive compounds that promote health. This research was, therefore, performed to shed light on the bioactivity and composition of different parts of Citrus australasica L. (peel and pulp). Initial ultrasound-assisted extraction using MeOH:H2O (80:20, v/v) was carried out. After that, four fractions (hexane, ethyl acetate, butanol and water) were generated through liquid–liquid partitioning, and the total phenolic content (TPC) and antioxidant activity were evaluated using the Folin–Ciocalteu and the ferric reducing antioxidant power (FRAP) assays, respectively. The ethyl acetate fraction in the peel, which presented the highest values of TPC and antioxidant activity, was characterized using high-performance liquid chromatography coupled to quadrupole time-of-flight (HPLC-QTof) mass spectrometry. Fifteen compounds were identified, of which seven were characterized for the first time in this matrix. Moreover, ten phenolic compounds were quantified using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The major compounds in the sample were citric acid, pyrogallol, caffeic acid, coumarin, rutin, naringin, 2-coumaric acid, didymin, naringenin and isorhamnetin, which were found in a range from 2.7 to 8106.7 µg/g sample dry weight. Finally, the results presented in this novel work confirmed that the peel by-product of C. australasica L. is a potential source of bioactive compounds and could result in a positive outcome for the food, cosmetics and pharmaceutical industries.

Discovery of Active Ingredients Targeted TREM2 by SPR Biosensor-UPLC/MS Recognition System, and Investigating the Mechanism of Anti-Neuroinflammatory Activity on the Lignin-Amides from Datura metel Seeds

As a new target protein for Alzheimer’s disease (AD), the triggering receptor expressed on myeloid Cells 2 (TREM2) was expressed on the surface of microglia, which was shown to regulate neuroinflammation, be associated with a variety of neuropathologic, and regarded as a potential indicator for monitoring AD. In this study, a novel recognition system based on surface plasmon resonance (SPR) for the TREM2 target spot was established coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC-MS), in order to screen the active ingredients targeting TREM2 from Datura metel seeds. The results showed that four lignan-amides were discovered as candidate compounds by SPR biosensor-UPLC/MS recognition analysis. According to the guidance of the active ingredients discovered by the system, the lignin-amides from Datura metel seeds (LDS) were preliminarily identified as containing 27 lignan-amides, which were enriched compositions by the HP-20 of Datura metel seeds. Meanwhile, the anti-inflammatory activity of LDS was evaluated in BV2 microglia induced by LPS. Our experimental results demonstrated that LDS could reduce NO release in LPS-treated BV2 microglia cells and significantly reduce the expression of the proteins of inducible Nitric Oxide Synthase (iNOS), cyclooxygenase 2 (COX-2), microtubule-associated protein tau (Tau), and ionized calcium-binding adapter molecule 1 (IBA-1). Accordingly, LDS might increase the expression of TREM2/DNAX-activating protein of 12 kDa (DAP12) and suppress the Toll-like receptor SX4 (TLR4) pathway and Recombinant NLR Family, Pyrin Domain Containing Protein 3 (NLRP3)/cysteinyl aspartate specific proteinase-1 (Caspase-1) inflammasome expression by LDS in LPS-induced BV2 microglial cells. Then, the inhibitory release of inflammatory factors Interleukin 1 beta (IL-1β), Interleukin 6 (IL-6), and Tumor necrosis factor-alpha (TNFα) inflammatory cytokines were detected to inhibit neuroinflammatory responses. The present results propose that LDS has potential as an anti-neuroinflammatory agent against microglia-mediated neuroinflammatory disorders.

Tangeretin maintains antioxidant activity by reducing CUL3 mediated NRF2 ubiquitination

To explore the antioxidant capacity of citrus flavonoids under different evaluation systems, chemical and biological methods were engaged to determine the antioxidant abilities of flavanones and polymethoxyflavones. Results showed that flavanones exhibited good antioxidant activity, while polymethoxyflavones had a weak ability to scavenge free radicals. Both flavanones and polymethoxyflavones exerted the ability to inhibit H₂O₂-induced oxidative stress, but the effective concentration of polymethoxyflavones was lower. Further exploration showed that neohesperidin and tangeretin selectively regulated antioxidant enzyme activity, both in vitro and in vivo. Tangeretin also maintained the expression of antioxidant enzymes in L02 cells and in ICR mice liver. The mechanism exploration showed that both neohesperidin and tangeretin promoted the expression of NRF2 and inhibit the expression of KEAP1, but tangeretin could inhibit the ubiquitination of NRF2 by inhibiting CUL3. The mechanism was verified by CUL3 gene silencing. This study demonstrates a novel antioxidant mechanism of natural products.

Chemical characterization and in vivo antioxidant activity of parsley (Petroselinum crispum) aqueous extract

Twenty-nine flavonoid glycosides were identified in the aqueous extract (PC) of Petroselinum crispum var. crispum leaves and apiin, the major compound, was isolated thereof. Apigenin was obtained (90% purity) by the hydrolysis of apiin. A high content of phenolics (12.49 ± 1.70 mg GAE per g of parsley extract - Folin-Ciocalteu method) and total flavonoids (15.05 ± 2.20 mg of quercetin equivalents per g of parsley extract - aluminum chloride method) was quantified in P. crispum, as well as high antioxidant activity ((EC50 - 15.50 mg mL-1, DPPH method) and (189.8 mM Fe(ii) per mg of dry plant aqueous extract - FRAP method)). In vivo analysis with Saccharomyces cerevisiae cells showed low toxicity of the aqueous extract of parsley, however, it revealed a high dose-dependent antioxidant potential, mainly in the lipoperoxidation assay. In addition, flavonoid apiin also showed antioxidant action on yeast cells under oxidative stress in the cell viability assay (0.1 mM) and lipid peroxidation (0.01 and 0.1 mM), while apigenin was slightly antioxidant. Therefore, it is likely that the antioxidant activity of apiin is related to the total antioxidant capacity of parsley.

Limonin induces apoptosis of HL-60 cells by inhibiting NQO1 activity

Limonin is an important bioactive substance in citrus fruits, especially in seeds, which has great potential in cancer prevention and treatment. In order to explore the anticancer activity based on interaction between limonin and NQO1, Human promyelocytic leukemia cells (HL-60) were studied in vitro. We found that limonin could inhibit proliferation and promote apoptosis of HL-60 cells, and the effect was positively correlated with its dosage. Western blot results showed that limonin could activate the endogenous apoptosis pathway mediated by mitochondria via up-regulating pro-apoptotic proteins (Bax, cytochrome c, Caspase3, and Caspase9) and down-regulating anti-apoptotic proteins (Bcl-2), thus inhibiting the proliferation of HL-60 cells and promoting apoptosis, which further proved the anticancer activity of limonin from the molecular mechanism. At the same time, limonin down-regulated the expression of NQO1, indicating that limonin may indirectly act on the apoptosis pathway by regulating the expression activity of antioxidant enzymes in vivo, thus exerting its inhibitory effect on tumor cells, which provides an idea for the molecular mechanism that natural products can indirectly exert their anticancer effect by regulating the activity of antioxidant enzymes.

Citrus flavonoids and their antioxidant evaluation

The antioxidant ability is the link and bridge connecting a variety of biological activities. Citrus flavonoids play an essential role in regulating oxidative stress and are an important source of daily intake of antioxidant supplements. Many studies have shown that citrus flavonoids promote health through antioxidation. In this review, the biosynthesis, composition and distribution of citrus flavonoids were concluded. The detection methods of antioxidant capacity of citrus flavonoids were divided into four categories: chemical, cellular, animal and clinical antioxidant capacity evaluation systems. The modeling methods, applicable scenarios, and their relative merits were compared based on these four systems. The antioxidant functions of citrus flavonoids under different evaluation systems were also discussed, especially the regulation of the Nrf2-antioxidases pathway. Some shortcomings in the current research were pointed out, and some suggestions for progress were put forward.

Polymethoxyflavones from citrus inhibited gastric cancer cell proliferation through inducing apoptosis by upregulating RARβ, both in vitro and in vivo

In order to discover the active anti-tumor ingredients during the flavonoids separation process of Ougan (Citrus reticulata cv. Suavissima), gastric cancer cell lines including AGS, BGC-823, and SGC-7901 were employed to evaluate the proliferation inhibition abilities of Ougan extracts, flavanone components, polymethoxyflavone components, neohesperidin, nobiletin, tangeretin, and 5-demethylnobiletin. Quantitative real-time PCR was used to detect the expression of three retinoic acid receptor genes, including RARA, RARB, and RARG. Western blot and immunohistochemistry were used to detect protein expressions. The results showed that the polymethoxyflavone components and the PMFs monomers inhibited the proliferation of three gastric cancer cell lines and induced apoptosis. The mechanism exploration found that PMFs up-regulated the expression of the RARB gene selectively and activated the Caspase3, 9, and PARP1 proteins. In addition to 5-demethylnobiletin, other PMFs also upregulated the expression of cleaved Caspase8. The mechanism was preliminarily verified by a RARβ inhibitor AGN 193109. Moreover, a nude mice tumor xenograft model confirmed the tangeretin could exhibit in vivo anti-tumor effect through inducing apoptosis and upregulating RARβ protein. All result suggested that tangeretin may be a potentially novel, safe and effective drugs with less toxicity and lesser side effects for gastric cancer therapeutics.

Analysis of Phenolic Components and Related Biological Activities of 35 Apple (Malus pumila Mill.) Cultivars

Apple (Malus pumila Mill.) is a popular fruit with high economic values and various biological activities that are beneficial to human health. In this study, 35 apple cultivars were collected and were evaluated for their basic quality indexes, phenolic compositions, antioxidant activity, anti-tumour, and anti-diabetic activities. The compositions of phenolics were detected by using high-performance liquid chromatography (HPLC) and high-resolution mass spectroscopy (HRMS) assays. The antioxidant activities of peel and pulp extracts from 35 apple cultivars were evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay and ferric reducing antioxidant power (FRAP) assay. Results showed that the contents of phenolic acids and proanthocyanidins showed significant correlations with the antioxidant activities. Phenolic-rich extracts significantly inhibited HepG2 cell proliferation, with the inhibition activity varied significantly between cultivars. ‘Gold Delicious’ pulp extract, ‘Xiboliyabaidian’ peel and pulp extracts showed protective effects on H₂O₂-induced injury of human umbilical vein endothelial cells (HUVEC). ‘Red Fuji’ peel extract, ‘Xiboliyabaidian’ peel and pulp extracts, as well as ‘Gold Delicious’ peel extract, significantly increased glucose consumption of HepG2 cells, in a dose-dependent manner. This research may provide theoretical guidance for further nutritional investigation of the apple resources.

Target-Genes Reveal Species and Genotypic Specificity of Anthocyanin Pigmentation in Citrus and Related Genera

Background: Anthocyanin pigmentation characterizes a number of tissues of Citrus and its relatives. The gain and loss of pigmentation is intriguing and is inherited variously among species. Methods: Citrus germplasm was used to investigate the anthocyanin pigmentation of tissues never before considered, including stamen, style and stigma, and of young leaves, petals, rind and flesh of 28 genotypes belonging to 14 species. Citrus genotypes encompassed citron, lemon, sweet orange, lime, and Citrus relatives included Microcitrus, Murraya, and Severinia. A relative qRT-PCR analysis was carried out on the structural and regulatory genes: phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3′-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), uridine diphosphate glucose flavonoid glucosyl-transferase (UFGT), glutathione S-transferase (GST), Ruby and Noemi. Image analysis and a genomic approach were employed to evaluate how the red pigmentation is inherited among tissues and species. Results: Pigmentation of young leaves and petals is specific to citron and its hybrids. Ruby controls the pigmentation of petals, but not of leaves. The red color of the rind and flesh is a trait that particularly characterizes a diversity of sweet oranges, citron hybrids and Citrus relatives. Color expression depends on external factors and also on developmental stage. The coloration of stamen and style is citron-specific, while a red stigma is exclusive to Moro orange and its hybrids. Conclusion: It is hypothesized that there is a relationship among Citrus species and genes controlling anthocyanin pigmentation.

Untargeted and Targeted Metabolomic Profiling of Australian Indigenous Fruits

Selected Australian native fruits such as Davidson's plum, finger lime and native pepperberry have been reported to demonstrate potent antioxidant activity. However, comprehensive metabolite profiling of these fruits is limited, therefore the compounds responsible are unknown, and further, the compounds of nutritional value in these native fruits are yet to be described. In this study, untargeted and targeted metabolomics were conducted using the three fruits, together with assays to determine their antioxidant activities. The results demonstrate that targeted free and hydrolysed protein amino acids exhibited high amounts of essential amino acids. Similarly, important minerals like potassium were detected in the fruit samples. In antioxidant activity, Davidson's plum reported the highest activity in ferric reducing power (FRAP), finger lime in antioxidant capacity (ABTS), and native pepperberry in free radical scavenging (DPPH) and phosphomolybdenum assay. The compounds responsible for the antioxidant activity were tentatively identified using untargeted GC×GC-TOFMS and UHPLC-QqQ-TOF-MS/MS metabolomics. A clear discrimination into three clusters of fruits was observed using principal component analysis (PCA) and partial least squares (PLS) analysis. The correlation study identified a number of compounds that provide the antioxidant activities. GC×GC-TOFMS detected potent aroma compounds of limonene, furfural, and 1-R-α-pinene. Based on the untargeted and targeted metabolomics, and antioxidant assays, the nutritional potential of these Australian bush fruits is considerable and supports these indigenous fruits in the nutraceutical industry as well as functional ingredients for the food industry, with such outcomes benefiting Indigenous Australian communities.

Characterization of a Flavonoid 3'/5'/7-O-Methyltransferase from Citrus reticulata and Evaluation of the In Vitro Cytotoxicity of Its Methylated Products

O-methylation of flavonoids is an important modification reaction that occurs in plants. O-methylation contributes to the structural diversity of flavonoids, which have several biological and pharmacological functions. In this study, an O-methyltransferase gene (CrOMT2) was isolated from the fruit peel of Citrus reticulata, which encoding a multifunctional O-methyltransferase and could effectively catalyze the methylation of 3’-, 5’-, and 7-OH of flavonoids with vicinal hydroxyl substitutions. Substrate preference assays indicated that this recombinant enzyme favored polymethoxylated flavones (PMF)-type substrates in vitro, thereby providing biochemical evidence for the potential role of the enzyme in plants. Additionally, the cytotoxicity of the methylated products from the enzymatic catalytic reaction was evaluated in vitro using human gastric cell lines SGC-7901 and BGC-823. The results showed that the in vitro cytotoxicity of the flavonoids with the unsaturated C2-C3 bond was increased after being methylated at position 3’. These combined results provide biochemical insight regarding CrOMT2 in vitro and indicate the in vitro cytotoxicity of the products methylated by its catalytic reaction.

Extraction and characterization of phenolic compounds with antioxidant and antimicrobial activities from pickled radish

The pickled radish can be kept at room temperature for years without spoilage. 2,6-dihydroxyacetophenone (DHAP), 4-hydroxybenzaldehyde (HBA), and 4-hydroxyphenethyl alcohol (4-HPEA) were first found from the pickled radish. The structures of three phenolic compounds were elucidated by analysis of their nuclear magnetic resonance and high-resolution electro-spray ionization mass spectrometry data. All these phenolic compounds showed good free radical scavenging capacity except HBA. Both DHAP and 4-HPEA also showed high ferric reducing ability. DHAP showed good antimicrobial activity against Escherichia coli, Bacillus subtilis, and Canidia albicans. HBA demonstrated antimicrobial activity against E. coli and C. albicans but not B. subtilis. Based on the results of MTT assay, these compounds did not show cytotoxicity to LO2 cell line. All results indicated the pickled radish had antioxidant and antimicrobial phenolic compounds. To the best of our knowledge, this report is the first to answer partially the question of why pickled foods can be kept at room temperature for years without spoilage based on the evidence of three phenolic compounds.

Green Tea Polyphenol (-)-Epigallocatechin Gallate (EGCG) Attenuates Neuroinflammation in Palmitic Acid-Stimulated BV-2 Microglia and High-Fat Diet-Induced Obese Mice

Obesity is closely associated with neuroinflammation in the hypothalamus, which is characterized by over-activated microglia and excessive production of pro-inflammatory cytokines. The present study was aimed at elucidating the effects of (−)-epigallocatechin gallate (EGCG) on palmitic acid-stimulated BV-2 microglia and high-fat-diet-induced obese mice. The results indicated the suppressive effect of EGCG on lipid accumulation, pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) release, and microglial activation in both cellular and high-fat-diet rodent models. These results were associated with lower phosphorylated levels of the janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT3) signaling pathway. In conclusion, EGCG can attenuate high-fat-induced hypothalamic inflammation via inhibiting the JAK2/STAT3 signaling pathways in microglia.