Finger Lime Research Articles

Effect of Silver Nitrate and Silver Thiosulphate on In Vitro Shoot Regeneration of Australian Pink Finger Lime (Citrus australasica cv. Mia Rose)

Citrus australasica, commonly known as the finger lime, is a distinctive fruit indigenous to the coastal rainforest of Australia. It is renowned for its unique appearance, tangy flavor, and multiple medicinal properties. Additionally, its unique caviar-like pulp has garnered significant attention in the culinary industry. Conventional propagation of C. australasica is challenged by incompatibility issues during grafting and budding, its monoembryonic nature, and the lengthy time required to flower and bear fruits. Micropropagation on the other hand is an efficient alternative to conventional propagation for various commercial crops including citruses. However, the issue of leaf abscission was previously observed in C. australasica cultures, which has resulted in reduced shoot viability. The current study aimed to determine the effects of silver nitrate (AgNO3) and silver thiosulphate (STS) on in vitro shoot regeneration of C. australasica cv. Mia Rose. Nodal explants were cultured on half-strength Murashige and Skoog (MS) media supplemented with AgNO3 at 2.00, 4.00, 6.00, 8.00, and 10.00 mg/L and STS at 10.00, 20.00, 40.00, 60.00 and 80.00 µM in combination with 2.00 mg/L 6-benzylaminopurine (BAP). Results demonstrated that 4.00 mg/L AgNO3 resulted in the highest shoot number and length (2.65 ± 0.18 and 0.27 ± 0.03 cm respectively), while treatment with 10.00 µM STS resulted in the highest number of shoots and shoot length (2.36 ±0.19 and 0.32 ± 0.04 cm respectively). No leaf abscission was observed for all treatments of AgNO3 and STS after eight weeks of culture. This study underscored the efficacy of AgNO3 and STS as potent ethylene antagonists in shoot cultures of C. australasica cv. Mia Rose, suggesting their potential utilization in the micropropagation of the finger lime species.

Exploring the use of portable infrared spectroscopy as a quality assurance tool for the Australian Native/Traditional food industry: a case study on finger lime (Citrus australasica)

SummaryFinger limes (Citrus australasica) are an Australian native and traditional food that are known for their caviar‐like pearls often referred to as “Citrus Caviar”. This study aimed to spectrally characterise finger lime varieties sourced across South‐East Queensland and Northern New South Wales. The varieties investigated demonstrated a wide diversity in their phenotypic appearance; however, their infrared spectra were similar. The NIR spectra of the samples were collected using a portable instrument and the data analysed using principal component analysis (PCA) and partial least squares (PLS) regression. Differences in the PCA score plot were observed associated with the different varieties analysed. The cross‐validation statistics obtained for the prediction of adulteration of finger with Tahitian lime were R2CV and SECV 0.96% and 7%, respectively (using 8 PLS factors), using PLS regression. This study demonstrated that a portable handheld NIR instrument is able to identify finger lime varieties using both whole fruits and the corresponding peel samples. This study also showed that NIR was able to identify the level of adulteration of finger lime with Tahitian lime.

A Flexible MXene-Black Phosphorus/Zinc Oxide Hybrid Structure with Excellent UVA-Specific Photoelectric Sensing Properties for Human Skin Protection.

Ultraviolet A (UVA) radiation causes various irreversible damages to human skin, so the research about UVA-specific sensing device is urgent. 2D black phosphorus (BP) is used in many photosensors due to its advantages of high carrier mobility and tunable bandgap, but its application for UVA-specific photosensor is not reported. Here, a MXene-BP/Zinc oxide (ZnO) hybrid structure with lamellar-spherical interfaces like finger lime fruit is prepared by the layer-by-layer assembly (LLA) method, and p-n junctions are constructed between BP and ZnO with the Ti3C2Tx electrode, showing excellent photoelectric performance. Density functional theory (DFT) calculations demonstrate that the enhanced performance is attributed to the rapid separation of photogenerated carriers in the presence of a built-in electric field at interface. Furthermore, a flexible MXene-BP/ZnO based UVA-specific photosensor is prepared, which shows a specific response to UVA as high as 7 mAW-1 and excellent mechanical stability, maintaining 98.46% response after 100 bending cycles. In particular, the integrated anti-UVA skin protection device shows excellent UVA-specific identification and wireless transmission capability, which can provide timely UVA exposure information and skin protection warning for the visually impaired. This work demonstrates a new approach for further developments of advanced photoelectric sensing technology toward improving people's skin health protection.

Antibacterial Activity of Ethanol Extract from Australian Finger Lime.

Australian finger lime (Citrus australasica L.) has become increasingly popular due to its potent antioxidant capacity and health-promoting benefits. This study aimed to determine the chemical composition, antibacterial characteristics, and mechanism of finger lime extract. The finger lime extracts were obtained from the fruit of the Australian finger lime by the ethanol extraction method. The antibacterial activity of the extract was examined by detecting the minimum inhibitory concentration (MIC) for two Gram-positive and four Gram-negative bacterial strains in vitro, as well as by assessing variations in the number of bacteria for Candidatus Liberibacter asiaticus (CLas) in vivo. GC-MS analysis was used to identify the antibacterial compounds of the extract. The antibacterial mechanisms were investigated by assessing cell permeability and membrane integrity, and the bacterial morphology was examined using scanning electron microscopy. The extract demonstrated significant antibacterial activity against Staphylococcus aureus, Bacillus subtilis, and Gram-negative bacterial species, such as Escherichia coli, Agrobacterium tumefaciens, Xanthomonas campestris, Xanthomonas citri, and CLas. Among the six strains evaluated in vitro, B. subtilis showed the highest susceptibility to the antimicrobial effects of finger lime extract. The minimum inhibitory concentration (MIC) of the extract against the tested microorganisms varied between 500 and 1000 μg/mL. In addition, the extract was proven effective in suppressing CLas in vivo, as indicated by the lower CLas titers in the treated leaves compared to the control. A total of 360 compounds, including carbohydrates (31.159%), organic acid (30.909%), alcohols (13.380%), polyphenols (5.660%), esters (3.796%), and alkaloids (0.612%), were identified in the extract. We predicted that the primary bioactive compounds responsible for the antibacterial effects of the extract were quinic acid and other polyphenols, as well as alkaloids. The morphology of the tested microbes was altered and damaged, leading to lysis of the cell wall, cell content leakage, and cell death. Based on the results, ethanol extracts from finger lime may be a fitting substitute for synthetic bactericides in food and plant protection.

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.

Physical, colour, and mechanical properties of pearls (citrus caviar) from three finger lime (Citrus australasica) varieties: Implications for economic value, quality grading, and benchmarking

Citrus australasica, the Australian finger lime or caviar lime have garnered interest both in culinary and scientific communities. Despite extensive studies on their metabolomic and volatilomic profiles, research on the physical properties of finger lime pearls, especially their diameter, colour, and mechanical properties, remains limited. Understanding these attributes is crucial for quality assessment, consumer preference, and marketability in the food industry. This study aims to investigate the diameter, visual appearance, and mechanical properties of finger lime pearls from three different varieties (‘Champagne Red’, ‘Emerald’, and ‘Chartreuse’), comparing them with similar foods and assessing their implications for culinary use and market value. Colour properties were analysed using the CIELAB system, and mechanical properties were assessed through texture analysis, focusing on bursting strength and strain. Finger lime pearl diameters ranged between 1.62 and 3.60 mm, aligning with sizes of comparative foods. Colour analysis revealed distinct differences among varieties. Mechanical properties, particularly bursting strength, and strain, varied significantly across varieties, with ‘Champagne Red’ and ‘Chartreuse’ showing higher bursting strengths. These properties suggest different culinary applications and potential for a grading system based on sensory experience. The study highlights the importance of physical and mechanical properties in determining the quality and marketability of finger lime pearls. It introduces a novel framework for assessing these attributes, suggesting that finger lime varieties can be differentiated and graded for culinary use based on pearl diameter, colour, and mechanical properties. This research lays the groundwork for future sensory-based studies and the development of quality grading systems for finger limes.

Chromosome-Scale, De Novo, Phased Genome Assemblies of Three Australian Limes: Citrus australasica, C. inodora, and C. glauca.

Huanglongbing (HLB) is a severe citrus disease worldwide. Wild Australian limes like Citrus australasica, C. inodora, and C. glauca possess beneficial HLB resistance traits. Individual trees of the three taxa were extensively used in a breeding program for over a decade to introgress resistance traits into commercial-quality citrus germplasm. We generated high-quality, phased, de novo genome assemblies of the three Australian limes using PacBio long-read sequencing. The genome assembly sizes of the primary and alternate haplotypes were determined for C. australasica (337 Mb/335 Mb), C. inodora (304 Mb/299 Mb), and C. glauca (376 Mb/379 Mb). The nine chromosome-scale scaffolds included 86-91% of the genome sequences generated. The integrity and completeness of the assembled genomes were estimated to be at 97.2-98.8%. Gene annotation studies identified 25,461 genes in C. australasica, 27,665 in C. inodora, and 30,067 in C. glauca. Genes belonging to 118 orthogroups were specific to Australian lime genomes compared to other citrus genomes analyzed. Significantly fewer canonical resistance (R) genes were found in C. inodora and C. glauca (319 and 449, respectively) compared to C. australasica (576), C. clementina (579), and C. sinensis (651). Similar patterns were observed for other gene families associated with potential HLB resistance, including Phloem protein 2 (PP2) and Callose synthase (CalS) genes predicted in the Australian lime genomes. The genomic information on Australian limes developed in the present study will help understand the genetic basis of HLB resistance.

The genome of Citrus australasica reveals disease resistance and other species specific genes

BackgroundThe finger lime (Citrus australasica), one of six Australian endemic citrus species shows a high natural phenotypic diversity and novel characteristics. The wide variation and unique horticultural features have made this lime an attractive candidate for domestication. Currently no haplotype resolved genome is available for this species. Here we present a high quality, haplotype-resolved reference genome for this species using PacBio HiFi and Hi-C sequencing.ResultsHifiasm assembly and SALSA scaffolding resulted in a collapsed genome size of 344.2 Mb and 321.1 Mb and 323.2 Mb size for the two haplotypes. The nine pseudochromosomes of the collapsed genome had an N50 of 35.2 Mb, 99.1% genome assembly completeness and 98.9% gene annotation completeness (BUSCO). A total of 41,304 genes were predicted in the nuclear genome. Comparison with C. australis revealed that 13,661 genes in pseudochromosomes were unique in C. australasica. These were mainly involved in plant-pathogen interactions, stress response, cellular metabolic and developmental processes, and signal transduction. The two genomes showed a syntenic arrangement at the chromosome level with large structural rearrangements in some chromosomes. Genetic variation among five C. australasica cultivars was analysed. Genes related to defense, synthesis of volatile compounds and red/yellow coloration were identified in the genome. A major expansion of genes encoding thylakoid curvature proteins was found in the C. australasica genome.ConclusionsThe genome of C. australasica present in this study is of high quality and contiguity. This genome helps deepen our understanding of citrus evolution and reveals disease resistance and quality related genes with potential to accelerate the genetic improvement of citrus.

Celebrating Australian native foods through hospital foodservices: Engaging patients, staff and the broader community

Objective: The modern Australian diet is largely characterised by too few fruits and vegetables and too many discretionary foods. This is very different to how Indigenous Australians ate prior to colonisation. Native plants and seeds like bush tomatoes, warrigal greens, Kakadu plum and wattleseed are not common features of the contemporary Australian diet. We developed an initiative to incorporate native plants and seeds into a hospital inpatient menu to normalise their use and provide nutrition education to patients, staff and the community of the nutrition and sustainability benefits of native ingredients. Design: Between May and August 2022, the Chef’s Special menu (for privately funded patients) featured Australian native ingredients in all dishes. The nutritional benefits of native foods were communicated to patients through a printed brochure delivered with the menu, to foodservices staff through in-service training, and to the broader community through social media. Setting: Urban hospital in Brisbane, Australia. Method: Data were collected on acceptability, engagement and reach of the education initiative. Results: The initiative was successfully delivered, with more than 8,000 patient brochures distributed, 45 staff attending training, and social media reaching approximately 10,000 people. The most frequently ordered main meal on the menu was grilled snapper (fish) with macadamia Asian herb salad and finger lime. Conclusion: The work highlighted how the patient menu in hospital can serve as a useful tool to communicate nutrition education to patients, staff and the broader community. In addition, we reflect on the many opportunities to continue to celebrate the nutritional benefits of Australian native foods in healthcare settings.

An investigation of germplasm resources and phylogenetic analysis of finger lime in Hainan Province, China

An investigation of germplasm resources and phylogenetic analysis of finger lime in Hainan Province, China

A practical synthesis of 8‐methyldecanal

Abstract8‐methyldecanal is a characteristic ingredient of Australian finger lime (Citrus australasica), and has found important applications in flavour and fragrance industry. A novel and practical preparation method of 8‐methyldecanal is presented. Starting from cheap and readily available 6‐chloro‐1‐hexanol, 8‐methyldecanal was prepared in five steps with an overall yield of 50.7%.

Conserving Citrus Diversity: From Vavilov’s Early Explorations to Genebanks around the World

Citrus is among the most economically important fruit crops. Its vast species diversity and global production was observed by N.I. Vavilov during his international plant explorations from the early to mid-1900s. Currently, ex situ citrus collections located around the world conserve and protect citrus genetic resources, as revealed in a survey conducted in 2021. Responses were received from 43 collections in 27 countries, of which 35 provided data regarding collection composition, management practices, and security, as well as other information. The six largest citrus collections have between 1000 and 1735 accessions. The largest accession holdings are mandarins and sweet oranges, although all citrus fruit types are maintained: mandarin, sweet orange, lemon, pummelo, grapefruit, hybrids, lime, sour orange, citron, kumquat, papeda, finger lime, and crop wild relatives. Diseases pose significant threats to collections, though some collections are maintained in a clean-plant state as a result of intensive sanitation efforts. National and regional quarantine regulations often limit the export and import of citrus plants or propagative materials, thus limiting the availability of materials at an international level. Resources, both financial and human, are necessary to ensure the long-term safety and security of citrus collections on a global scale. Future efforts to develop citrus genebanking communities will provide opportunities for improved conservation, as well as collaborations and training.

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.

Insights into the mechanism of Huanglongbing tolerance in the Australian finger lime (Citrus australasica).

The Australian finger lime (Citrus australasica) is tolerant to Huanglongbing (HLB; Citrus greening). This species can be utilized to develop HLB tolerant citrus cultivars through conventional breeding and biotechnological approaches. In this report, we conducted a comprehensive analysis of transcriptomic data following a non-choice infection assay to understand the CaLas tolerance mechanisms in the finger lime. After filtering 3,768 differentially expressed genes (DEGs), 2,396 were downregulated and 1,372 were upregulated in CaLas-infected finger lime compared to CaLas-infected HLB-susceptible 'Valencia' sweet orange. Comparative analyses revealed several DEGs belonging to cell wall, β-glucanase, proteolysis, R genes, signaling, redox state, peroxidases, glutathione-S-transferase, secondary metabolites, and pathogenesis-related (PR) proteins categories. Our results indicate that the finger lime has evolved specific redox control systems to mitigate the reactive oxygen species and modulate the plant defense response. We also identified candidate genes responsible for the production of Cys-rich secretory proteins and Pathogenesis-related 1 (PR1-like) proteins that are highly upregulated in infected finger lime relative to noninfected and infected 'Valencia' sweet orange. Additionally, the anatomical analysis of phloem and stem tissues in finger lime and 'Valencia' suggested better regeneration of phloem tissues in finger lime in response to HLB infection. Analysis of callose formation following infection revealed a significant difference in the production of callose plugs between the stem phloem of CaLas+ 'Valencia' sweet orange and finger lime. Understanding the mechanism of resistance will help the scientific community design strategies to protect trees from CaLas infection and assist citrus breeders in developing durable HLB tolerant citrus varieties.

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.

Citrus australasica F. Muell. Leaf Extracts are Ineffective Inhibitors of the Growth of a Panel of Bacterial Pathogens

Citrus australasica F. Muell. Leaf Extracts are Ineffective Inhibitors of the Growth of a Panel of Bacterial Pathogens

Phytochemical and Safety Evaluations of Finger Lime, Mountain Pepper, and Tamarind in Zebrafish Embryos.

Plants play a pivotal role in drug discovery, constituting 50% of modern pharmacopeia. Many human diseases, including age-related degenerative diseases, converge onto common cellular oxidative stress pathways. This provides an opportunity to develop broad treatments to treat a wide range of diseases in the ageing population. Here, we characterize and assess the toxicological effects of finger lime (Citrus australasica), mountain pepper (Tasmannia lanceolata), and small-leaved tamarind (Diploglottis australis) extracts. The characterization demonstrates that these Australian native plants have antioxidant potential and, importantly, they have high concentrations of distinct combinations of different antioxidant classes. Using zebrafish larvae as a high-throughput pre-clinical in vivo toxicology screening model, our experiment effectively discriminates which of these extracts (and at what exposure levels) are suitable for development towards future therapies. The LC50-96h for finger lime and tamarind were >480 mg/L, and 1.70 mg/L for mountain pepper. Critically, this work shows that adverse effects are not correlated to the properties of these antioxidants, thus highlighting the need for combining characterization and in vivo screening to identify the most promising plant extracts for further development. Thus, we present a high-throughput pre-clinical screening that robustly tests natural plant products to utilize the diversity of antioxidant compounds for drug development.

Poor Host Status of Australian Finger Lime, Citrus australasica, to Ceratitis capitata, Zeugodacus cucurbitae, and Bactrocera dorsalis (Diptera: Tephritidae) in Hawai'i.

Simple SummaryTephritid fruit flies are major economic pests for fruit production and impede international trade. Different host fruits are known to vary in their suitability for fruit flies to complete their life cycle. International regulatory standards that define the legal host status for tephritid fruit flies categorize fruits as a natural host, a conditional host, or a nonhost. For those fruits that are natural or conditional hosts, infestation rate can vary as a spectrum ranging from highly attractive fruits supporting large numbers of fruit flies to very poor hosts supporting low numbers. Finger lime, Citrus australasica, is a new crop in Hawai’i, and no information existed on its susceptibility to Hawai’i’s tephritid fruit fly pests. Host status testing was conducted using no-choice cage tests and field collections. Ceratitis capitata and Zeugodacus cucurbitae readily oviposited into finger limes, but individuals rarely developed to the pupal or adult stage. Finger lime was not infested by Bactrocera dorsalis and is probably a nonhost. For export, a postharvest treatment may still be required despite the very low infestation rate. Heat treatment, irradiation, and a systems approach are options to reduce the risk of exporting tephritid fruit flies in Hawai’i finger limes.We examined the host status of the Australian finger lime, Citrus australiasica F. Muell. (Rutaceae), to Hawai’i’s tephritid fruit fly pests using laboratory and field studies. In high-density (500 flies, 1:1 males and females) no-choice cage exposures (25 × 25 × 25-cm cage size), both undamaged and punctured finger limes were infested by Ceratitis capitata and Zeugodacus cucurbitae at a low rate compared to papaya controls, whereas Bactrocera dorsalis did not infest undamaged fruit, suggesting finger lime is a nonhost. In low-density (50 females) no-choice cage exposures, C. capitata and Z. cucurbitae readily oviposited in undamaged fruit but individuals rarely developed to the pupal or adult stage. For C. capitata, 274 finger limes exposed to 2000 gravid females, which laid an estimated 14,384 eggs, produced two pupae and no adults. For Z. cucurbitae, 299 fruit exposed to 2000 gravid females, which laid an estimated 4484 eggs, produced four pupae and one adult. Field sampling of undamaged fruit from the tree and off the ground from commercial farms produced five C. capitata pupa and one adult from 1119 fruit, for an infestation rate of 0.05 flies per kilogram of fruit; field collections found no natural Z. cucurbitae or B. dorsalis infestation, but the number of fruit available was too low to demonstrate nonhost status with a high degree of confidence.

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.

The complete chloroplast genome sequence of a Citrus australasica cultivar (Rutaceae）

Citrus australasica (F. Muell.) Swingle belongs to the family Rutaceae. Citrus australasica is native to eastern Australia and southeastern New Guinea, and is mainly concentrated in a small region of northern New South Wales and tropical rainforest areas in southern Queensland. The complete plastome length of C. australasica is 160,335 bp, with the typical structure and gene content of angiosperm plastids, including a 26,592 bp repeat B (IRB) region, 26,952 bp IRA, 87,678 bp large single copy (LSC) region and 18,756 bp small single copy (SSC) region. The plastid contains 135 genes, including 89 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The total G/C content of the C. australasica plastome is 38.4%. The complete plastome sequence of C. australasica will provide useful resources for conservation genetics research of this species and phylogenetic research of Rutaceae.