RP-HPLC–DAD-ESI-TOF–MS based strategy for new insights into the qualitative and quantitative phenolic profile in Tunisian industrial Citrus Limon by-product and their antioxidant activity

A robust method for quantifying 42 phenolic compounds by RP-HPLC/DAD: Columns performance and characterization of Brazilian Citrus peels

Reliable analytical methods are the basis for the elucidation of phenolic compounds in foods. This study aimed to optimize and validate a method for determining 42 phenolics using reverse-phase (RP) high-performance liquid chromatography (HPLC) coupled to diode-array-detector-DAD. The performance of two RP columns was evaluated. The 150x4.6 mm 3-μm column showed superior separation quality, whereas 35 of the 42 phenolics showed a separation resolution ≥1.5. The method's linearity, precision (coefficient variation< 3.09%), recovery (87.5-103.2%), specificity, limits of detection (0.04-0.25 mg/L), and quantification (0.06-0.25 mg/L) had acceptable ranges. Thirty phenolics were quantified in Citrus peels, mainly flavanones, flavanols, flavonols, and phenolic acids, highlighting the high values of hesperidin (535-35070 mg/kg) and naringin (26-36466 mg/kg). Lemon peels named 'Lisboa,' 'Thaiti,' 'Thaiti-2000', and 'Thaiti-2001' presented the main phenolics associated with antioxidant capacity. The presented method was robust for determining 42 phenolic compounds, offering a new approach for bioactive compound quantification in food matrices.

Lemon Peel Water Extract: A Novel Material for Retinal Health, Protecting Retinal Pigment Epithelial Cells against Dynamin-Related Protein 1-Mediated Mitochondrial Fission by Blocking ROS-Stimulated Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Pathway

Previous studies showed that NaIO3 can induce oxidative stress-mediated retinal pigment epithelium (RPE) damage to simulate age-related macular degeneration (AMD). Lemon peel is rich in antioxidants and components that can penetrate the blood-retinal barrier, but their role in retinal oxidative damage remains unexplored. Here, we explore the protection of lemon peel ultrasonic-assisted water extract (LUWE), containing large amounts of flavonoids and polyphenols, against NaIO3-induced retinal degeneration. We initially demonstrated that LUWE, orally administered, prevented retinal distortion and thinning on the inner and outer nuclei layers, downregulating cleaved caspase-3 protein expression in RPE cells in NaIO3-induced mice. The effect of LUWE was achieved through the suppression of apoptosis and the associated proteins, such as cleaved PARP and cleaved caspase-3, as suggested by NaIO3-induced ARPE-19 cell models. This is because LUWE reduced reactive oxygen species-mediated mitochondrial fission via regulating p-Drp-1 and Fis1 expression. We further confirmed that LUWE suppresses the expression of p-MEK-1/2 and p-ERK-1/2 in NaIO3-induced ARPE-19 cells, thereby providing the protection described above, which was confirmed using PD98059 and U0126. These results indicated that LUWE prevents mitochondrial oxidative stress-mediated RPE damage via the MEK/ERK pathway. Elucidation of the molecular mechanism may provide a new protective strategy against retinal degeneration.

Functional Ingredients and Additives from Lemon by-Products and Their Applications in Food Preservation: A Review

Citrus trees are among the most abundant fruit trees in the world, with an annual production of around 124 million tonnes. Lemons and limes are among the most significant contributors, producing nearly 16 million tonnes per year. The processing and consumption of citrus fruits generates a significant amount of waste, including peels, pulp, seeds, and pomace, which represents about 50% of the fresh fruit. Citrus limon (C. limon) by-products are composed of significant amounts of bioactive compounds, such as phenolic compounds, carotenoids, vitamins, essential oils, and fibres, which give them nutritional value and health benefits such as antimicrobial and antioxidant properties. These by-products, which are typically discarded as waste in the environment, can be explored to produce new functional ingredients, a desirable approach from a circular economy perspective. The present review systematically summarizes the potential high-biological-value components extracted from by-products to achieve a zero-waste goal, focusing on the recovery of three main fractions: essential oils, phenolic compounds, and dietary fibres, present in C. limon by-products, and their applications in food preservation.

Green Synthesis, Characterization, and Empirical Thermal Conductivity Assessment of ZnO Nanofluids for High-Efficiency Heat-Transfer Applications

ZnO nanoparticles were synthesized using lemon juice and zinc nitrate (1:1) through the green method. The structure of the biosynthesized ZnO nanoparticles was analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The morphology and the size of ZnO nanoparticles were elucidated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The powder was highly dispersed and irregularly shaped and the size of the nanoparticles ranged from 28 to 270 nm, depending on the shape of the particles. Thermal conductivity of the biosynthesized ZnO PG/W mixture 40:60 (v/v) nanofluids was measured within the temperature range of 20-70 °C. Experimental results revealed a linear increase in thermal conductivity with the rise of temperature and volume fraction. The enhancement of this parameter with temperature was probably due to the different shapes of the former agglomerates. They were broken by the thermal energy in aggregates of different forms. A correlation of these structures with temperature was established. Finally, an empirical model was developed for predicting thermal conductivity with particle volume fraction and temperature.

The profiles of durian (Durio zibethinus Murr.) shell phenolics and their antioxidant effects on H2O2-treated HepG2 cells as well as the metabolites and organ distribution in rats

Durian is a nutritious tropical fruit with potent antioxidant, anti-inflammatory, antibacterial and anti-cancer effects. However, the durian shell was mainly discarded as waste, while there were few studies on the characterization of its phenolic profiles, antioxidant activities, and in vivo metabolites. In the present study, a total of 17 compounds were identified in durian shell extract (DSE) by using an ultra-high-performance liquid chromatography coupled with linear ion trap quadrupole Orbitrap mass spectrometry (UHPLC-LTQ-Orbitrap-MS/MS), while 33 metabolites were found in rats' plasma, urine and organ. Moreover, DSE could effectively reduce H₂O₂-induced oxidative damage in HepG2 cells, reduce the expression of Reactive Oxygen Species (ROS), Malondialdehyde (MDA) and Lactate Dehydrogenase (LDH) and inhibit apoptosis by regulating the expression of Bcl-2-Associated X (BAX), B-Cell Lymphoma 2 (BCL-2), Caspase-3 and Caspase-9 genes and proteins related to mitochondrial pathway apoptosis. This is the first comprehensive report on Durian shell phenolics, their metabolic profiles and underlying mechanisms of the in vitro antioxidant activities.

Fluorescence of nanodiamond cocktails: pH-induced effects through interactions with comestible liquids

Fluorescent nanodiamonds with nitrogen-vacancy centers have become important nanoscale probes for sensing and imaging. The surface chemistry of the nanodiamonds influences their emission, interactions, and quantum properties. In this work, we propose to utilize fluorescent nanodiamonds as photostable markers for investigation of comestible liquids. We prepared nanodiamond/comestibles suspensions/cocktails with a wide range of pH levels and studied the samples via fluorescence, wettability, and zeta potential. The composition of the created cocktails revealed a strong impact on the properties of the nanodiamond and its surface chemistry, mainly induced by pH but also tuned by specific quenching compounds. Moreover, the stability of the nanodiamonds in the cocktail media was studied, along with various nature-originated compounds influencing their surface termination, polarity, and charge states. Thanks to the stability and biocompatibility of the nanodiamond, it can be applied in monitoring the condition of foodstuffs, and in the detection of toxins and pathogens in them.

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.

Fluorescence Intensity Enhancement of Green Carbon Dots: Synthesis, Characterization and Cell Imaging

The hydrothermal treatment of green carbon dots (CDs) is an appropriate fluorescent probe synthesis method. CDs are exploited as biological staining agents, especially for cellular detection and imaging. The nitrogen-doped green carbon dots (N-CDs) formation can improve the fluorescence intensity property in a one-step process. Here, we report two N-CDs from lemon and tomato extraction in the presence of hydroxylamine. Lemon and tomato N-CDs showed the blue fluorescence under ultraviolet radiation of about 360 nm. The characterization of CDs and N-CDs showed the presence of N-H and C-N bonds which enhanced the fluorescence efficiency. The mean size of lemon and tomato N-CDs were about 2 and 3 nm with an increased quantum yield (QY) of 5% and 3.38%, respectively. The CDs and N-CDs cytotoxicity assay exhibited high cell viability approximately 85% and 73%, respectively. N-CDs show superior fluorescent intensity in different solvents and significant stability under long-time UV irradiation, different PH and high ionic strength. Our results indicated that the use of N-CDs in cell imaging can lead to fluorescence intensity enhancement as well as proper biocompatibility. Therefore, the safe and high fluorescence intensity of green N-CDs can be utilized for fluorescent probes in biolabeling and bioimaging applications.

Modern Extraction and Purification Techniques for Obtaining High Purity Food-Grade Bioactive Compounds and Value-Added Co-Products from Citrus Wastes

Citrus contains a range of highly beneficial bioactive compounds, such as polyphenols, carotenoids, and vitamins that show antimicrobial and antioxidant properties and help in building the body's immune system. On consumption or processing, approximately 50% of the fruit remains as inedible waste, which includes peels, seeds, pulp, and segment residues. This waste still consists of substantial quantities of bioactive compounds that cause environmental pollution and are harmful to the ecosystem because of their high biological oxygen demand. In recent years, citrus cultivation and the production of processed foods have become a major agricultural industry. In addition to being a substantial source of economy, it is an ideal and sustainable and renewable resource for obtaining bioactive compounds and co-products for food and pharmaceutical industries. In the present article, the various methods of extraction, conventional and modern, as well as separation and isolation of individual bioactive compounds from the extraction mixture and their determination have been reviewed. This article presents both aspects of extraction methods, i.e., on a small laboratory scale and on an industrial mass scale. These methods and techniques have been extensively and critically reviewed with anticipated future perspectives towards the maximum utilization of the citrus waste.

Chemical components of Hyssopus cuspidatus Boriss.: isolation and identification, characterization by HPLC-DAD-ESI-HRMS/MS, antioxidant activity and antimicrobial activity

Eighteen compounds were isolated from the ethyl acetate fraction of the aerial part of Hyssopus cuspidatus. Their structures were established by analysis of mass and NMR data, as well as comparison with previous published data in the literatures. Among them, ten compounds were found from the Hyssopus genus for the first time, and one compound was isolated from H. cuspidatus for the first time. HPLC-DAD-ESI-HRMS/MS investigations was applied to further obtain the phenolic profiling of the ethyl acetate fraction, and nine derivatives of caffeic acid and ferulic or isoferulic acid were identified. Antioxidant activity against DPPH free radical and antibacterial activity against Candida albicans, Escherichia coli and Staphylococcus aureus were evaluated. The ethyl acetate fraction exhibited weak antioxidant activity and moderate antibacterial activity. The isolated compounds showed weak to potent antioxidant and antibacterial activity. To the best of our knowledge, this is the first report on the antioxidant and antibacterial activity of H. cuspidatus.

Characterisation of nutraceutical compounds from different parts of particular species of Citrus sinensis 'Ovale Calabrese' by UHPLC-UV-ESI-HRMS

Consumers are aware of diet causing health problems and therefore there is an increased demand for natural ingredients that are expected to be safe and health-promoting. Many of these compounds belong to the class of flavonoids and can be divided into these five groups: flavanones, flavones, flavonols, flavanols, isoflavones and anthocyanidins. Extracts from citrus fruits are usually used as functional ingredients for several products. The aim of this paper was to develop an UHPLC-UV-ESI-HRMS method to define the metabolite profile of different parts of citrus fruit, of a particular cultivar called 'Ovale Calabrese', and in its main by-products. The high resolution mass spectrometry analysis allowed the identification of 27 compounds belonging to the classes of flavonoids and terpenoids. The high contents of phytochemical compounds, reveal the potential use of the 'Ovale Calabrese' as a rich source of nutraceutical compounds.