Antioxidative and anti-inflammatory activities of Citrus unshiu peel extracts using a combined process of subcritical water extraction and acid hydrolysis

Current Treatments for COVID-19: Application of Supercritical Fluids in the Manufacturing of Oral and Pulmonary Formulations

Even though more than two years have passed since the emergence of COVID-19, the research for novel or repositioned medicines from a natural source or chemically synthesized is still an unmet clinical need. In this review, the application of supercritical fluids to the development of novel or repurposed medicines for COVID-19 and their secondary bacterial complications will be discussed. We envision three main applications of the supercritical fluids in this field: (i) drug micronization, (ii) supercritical fluid extraction of bioactives and (iii) sterilization. The supercritical fluids micronization techniques can help to improve the aqueous solubility and oral bioavailability of drugs, and consequently, the need for lower doses to elicit the same pharmacological effects can result in the reduction in the dose administered and adverse effects. In addition, micronization between 1 and 5 µm can aid in the manufacturing of pulmonary formulations to target the drug directly to the lung. Supercritical fluids also have enormous potential in the extraction of natural bioactive compounds, which have shown remarkable efficacy against COVID-19. Finally, the successful application of supercritical fluids in the inactivation of viruses opens up an opportunity for their application in drug sterilization and in the healthcare field.

Assessment of safety and health-benefits of Citrus hystrix DC. peel essential oil, with regard to its bioactive constituents in an in vitro model of physiological and pathological skin conditions

Citrus hystrix DC. peel essential oil (ChEO) has been reported to have many biological activities and is promoted for topical application. However, its effect on skin functioning has not yet been studied. This study aimed to evaluate its safety for normal skin cells as well as its potential activity against human melanoma. In addition, pro-inflammatory and anti-inflammatory activity was assessed, as well as inhibitory effects on important skin enzymes: tyrosinase and hyaluronidase. To better understand the complexity of the action of ChEO and the role of individual components, the study also included an evaluation of the activity of its main constituents: limonene, β-pinene, and terpinen-4-ol as well as two mixtures of these compounds, specially designed for this purpose: M1 in equal proportions (1:1:1) and M2 in proportions mimicking those found in the ChEO (2.6:1.7:1). The results showed that the essential oil of the C. hystrix peel, as well as its major components, was not cytotoxic to normal human skin cells representing various skin layers, namely keratinocytes (HaCaT), melanocytes (HEM), and fibroblasts (HDF), even after prolonged exposure of 72 h. The pro-inflammatory effect of ChEO, tested by caspase-1 activation in HaCaT cells, was less pronounced compared to limonene, β-pinene and terpinen-4-ol, and generally very low. On the other hand, its anti-inflammatory effect was noticeable and was half the potency of diclofenac sodium used as the reference drug. Although the anti-hyaluronidase activity of C. hystrix peel essential oil was lower compared to β-pinene and terpinen-4-ol, ChEO revealed fairly high anti-tyrosinase activity, with an enzyme inhibition level of over 80% at a concentration of 150-220 μg/ml. Studies on the potential anti-melanoma effect were performed using the LDH assay on three human cell lines of varying degrees of malignancy, namely WM793, A375, and HTB140. ChEO was more active than the tested single compounds or their mixtures. WM793 cells were found to be most susceptible, while HTB140 and A375 cells were slightly more resistant (IC₅₀ 59, 88 and 70 μg/ml, respectively). Our data indicate that ChEO is safe for the skin and has a perspective as an anti-melanoma agent.

Green Synthesis of Silver Nanoparticles Using Aqueous Citrus limon Zest Extract: Characterization and Evaluation of Their Antioxidant and Antimicrobial Properties

The current work concentrated on the green synthesis of silver nanoparticles (AgNPs) through the use of aqueous Citruslimon zest extract, optimizing the different experimental factors required for the formation and stability of AgNPs. The preparation of nanoparticles was confirmed by the observation of the color change of the mixture of silver nitrate, after the addition of the plant extract, from yellow to a reddish-brown colloidal suspension and was established by detecting the surface plasmon resonance band at 535.5 nm, utilizing UV-Visible analysis. The optimum conditions were found to be 1 mM of silver nitrate concentration, a 1:9 ratio extract of the mixture, and a 4 h incubation period. Fourier transform infrared spectroscopy spectrum indicated that the phytochemicals compounds present in Citrus limon zest extract had a fundamental effect on the production of AgNPs as a bio-reducing agent. The morphology, size, and elemental composition of AgNPs were investigated by zeta potential (ZP), dynamic light scattering (DLS), SEM, EDX, X-ray diffraction (XRD), and transmission electron microscopy (TEM) analysis, which showed crystalline spherical silver nanoparticles. In addition, the antimicrobial and antioxidant properties of this bioactive silver nanoparticle were also investigated. The AgNPs showed excellent antibacterial activity against one Gram-negative pathogens bacteria, Escherichia coli, and one Gram-positive bacteria, Staphylococcus aureus, as well as antifungal activity against Candida albicans. The obtained results indicate that the antioxidant activity of this nanoparticle is significant. This bioactive silver nanoparticle can be used in biomedical and pharmacological fields.

Effects of pretreatment and type of hydrolysis on the composition, antioxidant potential and HepG2 cytotoxicity of bound polyphenols from Tartary buckwheat (Fagopyrum tataricum L. Gaerth) hulls

This study investigated the effects of ultrasound assisted-subcritical water (U-SW), subcritical water (SW), ultrasound (U) and hot water (HW) pretreatments and acid hydrolysis (AH) and alkaline hydrolysis (AlkH) on the phenolic composition, antioxidant potential and cytotoxicity of Tartary buckwheat hull extracts. The Folin Ciocalteu assay and HPLC-MS were used to characterize and quantify phenolics of the extracts. The ABTS, FRAP and TEAC assays were used to measure antioxidant activity and the MTT assay was used to measure cytotoxicity of the extracts in HepG2 human liver cancer cells. Results showed that U-SW gave the best AH yield of phenolics (128.45), followed by SW (85.82) and U (64.70), compared to the control, HW (35.82 mgg^-1). The same trend was observed for phenols extracted using AlkH. U-SW had the highest antioxidant activity, followed by SW and U regardless of hydrolytic method used. Cytotoxicity followed a similar trend with U-SW and SW being the most cytotoxic to liver cancer cells, followed by U, with the least being HW. The findings suggested that plant materials such as Tartary buckwheat hulls can be pretreated with U-SW, SW and U prior to hydrolytic recovery of bound polyphenols. Also, AH was more efficient than AlkH for phenol extraction, and gave extracts with higher antioxidant activity and cytotoxicity in HepG2 liver carcinoma cells. This application allows for beneficial usage of agricultural biomass and help diversify income sources and products for industry.

Optimization of Vacuum-Microwave-Assisted Extraction of Natural Polyphenols and Flavonoids from Raw Solid Waste of the Orange Juice Producing Industry at Industrial Scale

Orange pomace (OP) is a solid waste produced in bulk as a byproduct of the orange juice industry and accounts for approximately 50% of the quantity of the fruits processed into juice. In numerous literature references there is information about diverse uses of orange pomace for the production of high-added-value products including production of natural antioxidant and antimicrobial extracts rich in polyphenols and flavonoids which can substitute the hazardous chemical antioxidants/antimicrobials used in agro-food and cosmetics sectors. In this work and for the first time, according to our knowledge, the eco-friendly aqueous vacuum microwave assisted extraction of orange pomace was investigated and optimized at real industrial scale in order to produce aqueous antioxidant/antimicrobial extracts. A Response Surface Optimization methodology with a multipoint historical data experimental design was employed to obtain the optimal values of the process parameters in order to achieve the maximum rates of extraction of OP total polyphenols and/or total flavonoids for economically optimum production at industrial scale. The three factors used for the optimization were: (a) microwave power (b) water to raw pomace ratio and (c) extraction time. Moreover, the effectiveness and statistical soundness of the derived cubic polynomial predictive models were verified by ANOVA.

Compressed fluids and phytochemical profiling tools to obtain and characterize antiviral and anti-inflammatory compounds from natural sources

Many natural compounds, found mainly in plants, are associated with the treatment of various diseases. The search for natural therapeutic agents includes compounds with antiviral and anti-inflammatory activities. Among the many steps involved in bioprospection, extraction is the first and most critical step for obtaining bioactive compounds. One of the main advantages of using compressed fluids extraction is the high quality of the final product obtained due to the use of green solvents, while the selectivity towards target compounds can be tuned by adjusting the process parameters, especially pressure, temperature and solvent characteristics. In this review, a discussion is provided on the power of compressed fluids, such as supercritical fluid extraction (SFE), pressurized liquid extraction (PLE) and subcritical water extraction (SWE) to obtain antiviral and anti-inflammatory compounds from natural sources. In addition, an adequate knowledge about the identity and quantity of the compounds present in the extract is essential to correlate biological activity with chemical composition. Phytochemical profiling tools used for identification and quantification of these bioactive natural compound are also discussed. It can be anticipated that after the current SARS-COV-2 pandemic, the search of new natural compounds with antiviral and anti-inflammatory activity will be a hot research topic, so, this review provides an overview on the technologies currently used that could help this research.

Innovative "Green" and Novel Strategies for the Extraction of Bioactive Added Value Compounds from Citrus Wastes-A Review

Citrus is a major processed crop that results in large quantities of wastes and by-products rich in various bioactive compounds such as pectins, water soluble and insoluble antioxidants and essential oils. While some of those wastes are currently valorised by various technologies (yet most are discarded or used for feed), effective, non-toxic and profitable extraction strategies could further significantly promote the valorisation and provide both increased profits and high quality bioactives. The present review will describe and summarize the latest works concerning novel and greener methods for valorisation of citrus by-products. The outcomes and effectiveness of those technologies such as microwaves, ultrasound, pulsed electric fields and high pressure is compared both to conventional valorisation technologies and between the novel technologies themselves in order to highlight the advantages and potential scalability of these so-called "enabling technologies". In many cases the reported novel technologies can enable a valorisation extraction process that is "greener" compared to the conventional technique due to a lower energy consumption and reduced utilization of toxic solvents.