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Summary Pummelo (Citrus maxima or Citrus grandis) is a basic species and an important type for breeding in Citrus. Pummelo is used not only for fresh consumption but also for medicinal purposes. However, the molecular basis of medicinal traits is unclear. Here, compared with wild citrus species/Citrus‐related genera, the content of 43 bioactive metabolites and their derivatives increased in the pummelo. Furthermore, we assembled the genome sequence of a variety for medicinal purposes with a long history, Citrus maxima ‘Huazhouyou‐tomentosa’ (HZY‐T), at the chromosome level with a genome size of 349.07 Mb. Comparative genomics showed that the expanded gene family in the pummelo genome was enriched in flavonoids‐, terpenoid‐, and phenylpropanoid biosynthesis. Using the metabolome and transcriptome of six developmental stages of HZY‐T and Citrus maxima ‘Huazhouyou‐smooth’ (HZY‐S) fruit peel, we generated the regulatory networks of bioactive metabolites and their derivatives. We identified a novel MYB transcription factor, CmtMYB108, as an important regulator of flavone pathways. Both mutations and expression of CmtMYB108, which targets the genes PAL (phenylalanine ammonia‐lyase) and FNS (flavone synthase), displayed differential expression between Citrus‐related genera, wild citrus species and pummelo species. This study provides insights into the evolution‐associated changes in bioactive metabolism during the origin process of pummelo.

The aim of the study was to compare the mineral content between the peel and the pulp of citrus fruits and to determine which citrus fruit, among orange ( Citrus sinensis ), pomelo ( Citrus maxima ), mandarin ( Citrus reticulata Blanco), lemon ( Citrus limon ), key lime ( Citrus aurantifolia ), and red, yellow, or green grapefruit ( Citrus paradisi ), is the richest in minerals. The research material consisted of fresh citrus fruits belonging to the genus Citrus L in the family Rutaceae. The fruits were purchased at a supermarket at one time. To prepare laboratory samples, each fruit was cut in half, and one half was homogenized, treating the sample as a whole (peel + flesh), while the other half was peeled and the pulp (F) and peel (P) were homogenized separately. To determine the content of minerals (Na + , K + , Ca +2 , Mg +2 , Fe +2 , Zn +2 , Cu +2 , Mn +2 , and Se +2 ), the samples were mineralized and analyzed using an Analytik Jena PlasmaQuant PQ 9000 inductively coupled plasma optical emission spectrometer. The content of macro- and micronutrients in the peel of most of the fruits far exceeded their quantity in the pulp. Oranges and pomelos are the fruits richest in iron and copper, so they could be recommended in cases such as hemoglobin production disorders resulting from a deficiency of these elements. Oranges can additionally enrich the body with potassium, phosphorus, and manganese, while lime can be a source of calcium, zinc, sodium, and especially potassium. It should also be noted that all citrus fruits are a very valuable source of potassium, which is needed to ensure the water and electrolyte balance.

Summary Pummelo (Citrus maxima) is a fundamental species of Citrus which contributes to most of the cultivated citrus, including sweet orange, lemon and etc. The fruit neck is a structural feature of pummelo, and a long fruit neck reduces the edible rate of the fruit. In this study, we assembled a telomere‐to‐telomere (T2T) gap‐free reference genome for the typical short fruit neck cultivar, ‘Pingshan’ pummelo, and a chromosome‐level genome for the typical long fruit neck cultivar, ‘Shatian’ pummelo. Here, we used a segment population derived from a cross between a long fruit neck cultivar (‘Guanxi’ pummelo) and a short fruit neck (‘Pingshan’ pummelo) cultivar to map the determinant controlling the fruit neck length. We identified a strong peak on chromosome 1 within the 27.5–30.5 Mb physical region and found a 52 bp deletion linked with the fruit neck length. Moreover, by combining RNA sequencing data of the fruit neck development and variation analysis, we identified two genes, one encodes ethylene‐responsive transcription factor (CgABR1) and the other encodes FAD‐dependent urate hydroxylase (CgFAD). Genetic transformation confirmed that overexpression of CgABR1 and CgFAD can inhibit fruit neck length. DNA affinity purification sequencing, electrophoretic mobility shift assays and dual‐LUC reporter assays demonstrated that CgABR1 can activate the expression of CgFAD by directly binding to its promoter. In summary, we assembled a T2T gap‐free genome for pummelo and identified the key genes for fruit neck length in citrus, offering an important resource and new genes for citrus genetic improvement and breeding programs.

Neohesperidosides are disaccharides that are present in some flavonoids and impart a bitter taste, which can significantly affect the commercial value of citrus fruits. In this study, we identified three flavonoid-7-O-di-glucosyltransferase (dGlcT) genes closely related to 1,2-rhamnosyltransferase (1,2RhaT) in citrus genomes. However, only 1,2RhaT was directly linked to the accumulation of neohesperidoside, as demonstrated by association analysis of 50 accessions and co-segregation analysis of an F₁ population derived from Citrus reticulata × Poncirus trifoliata. In transgenic tobacco BY2 cells, over-expression of CitdGlcTs resulted in flavonoid-7-O-glucosides being catalysed into bitterless flavonoid-7-O-di-glucosides, whereas over-expression of Cit1,2RhaT converted the same substrate into bitter-tasting flavonoid-7-O-neohesperidoside. Unlike 1,2RhaT, during citrus fruit development the dGlcTs showed an opposite expression pattern to CHS and CHI, two genes encoding rate-limiting enzymes of flavonoid biosynthesis. An uncoupled availability of dGlcTs and substrates might result in trace accumulation of flavonoid-7-O-di-glucosides in the fruit of C. maxima (pummelo). Past human selection of the deletion and functional mutation of 1,2RhaT has led step-by-step to the evolution of the flavor-related metabolic network in citrus. Our research provides the basis for potentially improving the taste in citrus fruit through manipulation of the network by knocking-out 1,2RhaT or by enhancing the expression of dGlcT using genetic transformation.

Flavonoid profile and antioxidant activity of citrus peels, pulps, and juices from 27 local citrus cultivars in China were investigated. Flavonoid composition and content were determined using UPLC-PDA. Total phenolic content (TPC) and total flavonoid content (TFC) were measured using a Folin–Ciocalteau reagent and Al(NO3)-NaNO2 complexometry, respectively. The antioxidant capacities of the extracts were evaluated by DPPH, ABTS and FRAP method, respectively. Citrus peel not only exhibited better antioxidant potential, but also presented more composition diversity and contained higher concentrations of flavonoids than pulp and juice. Different citrus species were characterized by their individual predominant flavonoids, contributing largely to the antioxidant activity, such as mandarin was characterized by hesperidin, nobiletin and tangeretin, while pummelo and papeda were characterized by naringin. The peel of Guihuadinanfeng (Citrus reticulata) had the highest TPC of 23.46 mg equivalent gallic acid/g DW (dry weight) and TFC of 21.37 mg equivalent rutin/g DW. Shiyueju (C. reticulata) peel showed the highest antioxidant capacity based on the antioxidant potency composite (APC) analysis. Overall, mandarin (C. reticulata) fruits peel contained more TPC and TFC, exhibiting higher antioxidant capacities than other species, and were good natural sources of flavonoids and antioxidants.

The study investigated the effect of albedo and flavedo extracts of grapefruit and pomelo on storage stability of turkey patties during refrigerated storage. Five different types of products were developed depending on the addition of extracts viz. control (C), albedo and flavedo extract of grapefruit (GA and GF), and albedo and flavedo extract of pomelo (PA and PF). The products were stored for 10 days and evaluated for lipid and protein oxidation, pH, colour and sensory properties. The extracts improved the lipid oxidative stability by decreasing (P < 0.05) the TBARS values of the samples compared to control group. No effect of the extract treatments (P > 0.05) was observed on pH and colour values of the products (a* and b*). The lowest TBARS values were found for the products containing GF (0.78 mg MA/kg) on day 4. The treatments showed a significant impact on flavour of the products and the highest scores were obtained for PA containing products.

The use of whole citrus fruits in the food industry means that the valuable peel is used, but this may raise palatability or health concerns among consumers. The content of sugars, dietary fibre, redox compounds, lead, and cadmium was compared in citrus fruits (orange; pomelo; mandarin; lemon; key lime; and red, yellow, and green grapefruit). The pulp of all fruits contained significantly less fibre, tannins, and phenolic compounds than the peel. Whole citrus fruits had significantly lower content of sugars and higher content of dietary fibre and phenolic compounds, including ferulic acid, than their pulps. Whole grapefruits had higher concentrations of ascorbic acid. Whole lemons, limes, and mandarins had higher antioxidant potential than their pulp, due to their higher content of ascorbic acid, tannins, and phenolic compounds. Lead and cadmium content in whole fruits, while higher than in the pulps, was well below the acceptable daily intake.

Background Pomelo is one of the three major species of citrus. The fruit accumulates a variety of abundant secondary metabolites that affect the flavor. UDP-glycosyltransferases (UGTs) are involved in the glycosylation of secondary metabolites. Results In the present study, we performed a genome-wide analysis of pomelo UGT family, a total of 145 UGTs was identified based on the conserved plant secondary product glycosyltransferase (PSPG) motif. These UGT genes were clustered into 16 major groups through phylogenetic analysis of these genes with other plant UGTs (A-P). Pomelo UGTs were distributed unevenly among the chromosomes. At least 10 intron insertion events were observed in these UGT genome sequences, and I-5 was identified to be the highest conserved one. The expression profile analysis of pomelo UGT genes in different fruit tissues during development and ripening was carried out by RNA-seq. Conclusions We identified 145 UGTs in pomelo fruit through transcriptome data and citrus genome database. Our research provides available information on UGTs studies in pomelo, and provides an important research foundation for screening and identification of functional UGT genes.

The decline of fossil- and ore-based materials is calling for more recycling of waste into new materials. Here, I review the recycling of ashes from biomass into reagents for chemical synthesis and biodiesel production. Biomass includes banana, pomegranate, rice, papaya, century plant, water hyacinth, bael fruit, nilgiri, mango, onion, muskmelon fruit, pomelo, lemon fruit, teak and tamarind. Chemical reactions include Knoevenagel condensation, Suzuki–Miyaura cross-coupling, Sonogashira reaction, Dakin reaction, Henry reaction, Ullmann coupling, Pd-catalyzed homocoupling, aromatic bromination, hydroxylation of arylboronic acids, hydration of nitriles and azide–alkyne click reaction. The synthesis of peptide bonds, disulfides, aminochromenes, carboxycoumarins, diazohydroxy esters, imidazopyridines, pyranopyrazoles, chalcones, flavones and bisenols is described.

Citrus fruits exhibit a high level of different phytoconstituents, of which the changes in the different parts of the fruit during ripening have not been thoroughly studied yet. Thus, in this study, we have investigated how different parts of pomelo fruit (Citrus grandis L.) are modified throughout the development of two consecutive growing seasons. In detail, the main phytochemical compounds, such as total phenolic content, total flavonoid content, antioxidant capacity, DPPH free radical scavenging activity, Ferric reducing antioxidant power (FRAP), and naringin and tannin content, were analyzed. A systematic metabolism of these compounds was found during the development of the fruit, but some pomelo tissues showed a fluctuating trend, suggesting a dependence on the different growing season. Focusing on the tissue distribution of these compounds, the fruit membrane contained the highest level of total phenolic and flavonoid content; fruit flavedo displayed the highest antioxidant capacities and FRAP activities, whereas maximum accumulation of naringin was noticed in fruit albedo. Instead, the highest DPPH free radical scavenging activity and tannin contents were found in the pomelo juice. Regarding the distribution of compounds, a possible bias pattern for the accumulation of those compounds has been noticed throughout the fruit development. From the GC-MS analysis, a total of 111 compounds were identified, where 91 compounds were common in both seasons. Overall, these results could be useful for the food processing industry as guidelines for excellent quality foods and for introducing health-beneficial products and components into our daily diets.