The research team, led by Mohamed T. Selim and Nashaat N. Mahmoud of the Botany and Microbiology Department, took a deliberately comparative approach. Rather than examining a single plant part or a single solvent, they prepared extracts of dried stems, leaves, and flowers using five solvents spanning a wide range of polarity: petroleum ether, ethyl acetate, acetone, methanol, and water. This polarity gradient matters because different classes of plant metabolites dissolve preferentially in solvents of different chemical character. Non-polar solvents such as petroleum ether tend to pull out lipids, waxes, and steroids, while highly polar water and methanol extract sugars, glycosides, tannins, and other hydrophilic compounds. By running the full spectrum, the researchers could determine exactly where the plant’s chemical treasure is concentrated.

Before any extraction began, the team characterized the proximate composition of each plant part, and the results revealed striking differences. The flowers carried the highest moisture content at 9.40 percent, while the stems were unusually mineral-rich, showing an ash content of 18.58 percent that exceeded both leaves and flowers. The flowers also proved to be the most nutritionally dense tissue, with a lipid content of 4.33 percent, a carbohydrate content of 66.16 percent, and a crude protein content of 15.29 percent. These baseline measurements are more than academic bookkeeping; they help determine which plant part is worth processing for which purpose, since a tissue dominated by carbohydrates will behave very differently in extraction and formulation than one rich in lipids or minerals.

When it came to extraction efficiency, solvent choice dominated the outcome. Water extracts delivered the highest percentage yield across the plant parts, followed by methanol, acetone, ethyl acetate, and finally petroleum ether. Among the plant tissues, leaves produced the maximum extract yield, with flowers and stems trailing behind. This pattern is chemically intuitive: oleander tissues are loaded with polar glycosides and phenolic compounds that dissolve readily in water and methanol but remain locked away from non-polar solvents. For anyone hoping to industrialize the process, the message is clear: the cheapest and greenest solvent, plain water, is also the most productive one, an encouraging alignment of economic and environmental incentives.

The phytochemical screening painted a detailed portrait of the plant’s defensive arsenal. Across the different parts, the researchers detected alkaloids, flavonoids, tannins, glycosides, steroids, coumarins, quinones, phenols, cardiac glycosides, and terpenoids, the full roster of secondary metabolites that plants typically deploy against microbes and herbivores. Two classes were conspicuously absent: saponins and anthraquinones were not found in any part of the plant. Anthocyanins, the pigments responsible for red and purple coloration, appeared exclusively in the flowers and were completely absent from stems and leaves. This tissue-specific distribution underscores a key principle of natural product chemistry: a plant is not a uniform bag of chemicals but a mosaic of specialized tissues, each with its own metabolic profile.

Quantitative assays sharpened that picture considerably. The acetone extract of the flowers emerged as the phytochemical powerhouse, registering the greatest levels of total phenols at 157.12 milligrams of gallic acid equivalents per gram, total flavonoids at 187.43 milligrams of quercetin equivalents per gram, and tannins at 89.93 milligrams of tannic acid equivalents per gram. At the opposite extreme, the petroleum ether extract of stems contained the lowest amounts of all three, at just 5.45, 6.43, and 3.45 milligrams per gram respectively. The roughly thirtyfold spread between these extremes illustrates how dramatically solvent polarity and plant tissue interact to determine the composition of an extract, and why screening studies of this kind are essential before any product development can begin.

The antimicrobial testing then put these chemical inventories to work. Using the agar well diffusion method, a standard technique in which extract-loaded wells are cut into plates seeded with microorganisms and zones of inhibited growth are measured, the team challenged six strains. The panel included Gram-positive bacteria Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633, Gram-negative bacteria Pseudomonas aeruginosa ATCC 9027, Salmonella Typhimurium ATCC 14028, and Escherichia coli ATCC 11229, and the unicellular fungal pathogen Candida albicans ATCC 10231. The extracts showed the ability to inhibit representatives of all these groups, a breadth of activity that spans both major bacterial membrane architectures as well as a eukaryotic pathogen responsible for serious infections in immunocompromised patients.

That broad-spectrum activity is significant in the context of the global antimicrobial resistance crisis. Gram-negative bacteria such as Pseudomonas aeruginosa and E. coli are wrapped in an outer membrane that excludes many conventional antibiotics and makes new drug development notoriously difficult, which is why the World Health Organization has flagged carbapenem-resistant Pseudomonas among its priority pathogens. Plant phenolics, tannins, and flavonoids are known to attack microbial cells through multiple mechanisms simultaneously, including membrane disruption, enzyme inhibition, and interference with quorum sensing, and this multi-target action makes resistance harder to evolve. The oleander extracts’ activity against both Gram-positive and Gram-negative organisms, along with Candida, suggests a complex mixture whose components complement one another rather than a single narrow-spectrum compound.

The study also carries a sustainability angle that fits squarely within the green chemistry movement. Oleander is fast-growing, drought-tolerant, and widely cultivated as an ornamental, which means substantial biomass is already generated through routine pruning in parks and along roadsides. Converting that low-value biomass into standardized bioactive extracts would require no dedicated agricultural land, and the finding that water, the greenest solvent of the five tested, gives the highest yields strengthens the environmental case further. The researchers note that the collection of plant material complied with WHO guidelines for the assessment of herbal medicines, and the work was conducted at the Faculty of Science of Al-Azhar University in Cairo with open access funding provided through Egypt’s Science, Technology and Innovation Funding Authority and the Egyptian Knowledge Bank.

Important caveats remain before oleander extracts could ever reach a pharmacy shelf or a food-preservation line. The plant’s cardiac glycosides, including the compounds known as oleandrin and nerine referenced in the study, are potently toxic to humans and animals, so any practical application would demand rigorous fractionation, toxicity testing, and dosage control to separate antimicrobial benefit from systemic danger. The current work was conducted in vitro, meaning the results demonstrate inhibition on agar plates rather than efficacy in living organisms, and standardization of extract composition would be essential given the natural variability of plant chemistry. Still, as a foundational map of where oleander’s bioactive chemistry lives, which solvents unlock it, and which microbes it can suppress, the study provides a credible starting point. It transforms a familiar poisonous shrub from a hazard into a candidate feedstock for the search for new natural antimicrobials at a moment when such candidates are urgently needed.

Subject of Research: Phytochemical composition and antimicrobial activity of Nerium oleander extracts obtained with different solvents

Article Title: Green extraction routes for conversion of Nerium oleander L. biomass into bioactive agents: phytochemical insights and antimicrobial promise

Article References: Selim, M. T., & Mahmoud, N. N. (2026). Green extraction routes for conversion of Nerium oleander L. biomass into bioactive agents: phytochemical insights and antimicrobial promise. BMC Complementary Medicine and Therapies, 26(1), Article 288. https://doi.org/10.1186/s12906-026-05594-x

Image Credits: AI Generated

DOI: 10.1186/s12906-026-05594-x

Keywords: Nerium oleander, phytochemistry, green extraction, antimicrobial activity, natural products, phenolics, flavonoids, cardiac glycosides, antimicrobial resistance, plant biomass, solvent extraction, Candida albicans

The investigation began with a deceptively simple question: does flower color correlate with leaf chemistry? Understanding phytochemical variability within a species matters because it shapes how researchers and industries select plant material for natural product discovery. If two visually distinct forms of the same tree accumulate different suites of phenolic compounds, then any pharmacological or food-industry application of E. sideroxylon could depend heavily on which form is harvested, and even on which solvent is used during extraction. The team therefore designed a systematic comparison, extracting leaf material from each form with both methanol and ethanol and then subjecting the resulting extracts to a battery of quantitative and analytical tests.

The quantitative results were striking. Methanolic extracts consistently outperformed their ethanolic counterparts in total secondary metabolite content, and the red-flowered form stood out with a total phenolic content reaching 528.40 milligrams of gallic acid equivalents per gram of dry weight. Condensed tannins were also abundant, peaking at 334.60 milligrams of tannic acid equivalents per gram of dry weight, while flavonoid contents ranged between 60.40 and 64.60 milligrams per gram of dry weight. These figures place E. sideroxylon among the more phenolic-rich eucalypts examined in the broader literature, and they underscore why solvent choice is such a critical variable: methanol, being more polar, appears to draw a richer load of phenolics out of the leaf matrix than ethanol does.

To move beyond bulk measurements, the researchers turned to high-performance liquid chromatography coupled with diode-array detection, a technique that separates individual compounds and records their characteristic light absorption spectra. This HPLC-DAD profiling allowed the tentative annotation of seventeen phenolic compounds, whose relative abundances shifted according to both the extraction solvent and the flower-color form. Rutin, myricetin and diosmin emerged as among the most abundant putatively assigned compounds in the methanolic extract of the white-flowered form, whereas morin hydrate was particularly prominent in the ethanolic extract of the red-flowered form. Such differences are chemically meaningful: rutin and myricetin are flavonoids with well-documented antioxidant behavior, while morin hydrate has attracted attention for its wide-ranging pharmacological potential.

Complementing the chromatography, the team applied attenuated total reflectance Fourier-transform infrared spectroscopy, or ATR-FTIR, a rapid fingerprinting method that identifies functional groups within a sample by measuring how its molecular bonds absorb infrared light. The spectra revealed absorption features consistent with phenolic compounds, including signals attributable to hydroxyl groups and aromatic ring structures, and the spectroscopic patterns supported the trends observed chromatographically. This dual confirmation matters because it demonstrates that two independent analytical windows, one separation-based and one vibration-based, tell a coherent story about the chemical composition of the extracts, lending weight to the tentative compound assignments made by HPLC-DAD alone.

Biological testing followed, and the extracts delivered a series of concentration-dependent effects. In the DPPH radical scavenging assay, a standard measure of antioxidant capacity, all four extracts neutralized free radicals in a dose-dependent fashion, with the methanolic extracts again leading the pack. The white-flowered methanolic extract achieved an IC50 of 109.30 micrograms per milliliter, meaning that concentration sufficed to quench half of the radicals present, while the red-flowered methanolic extract required 151.10 micrograms per milliliter. Lower IC50 values indicate stronger antioxidant activity, so the white-flowered form’s methanolic extract was the most potent radical scavenger in this comparison, an outcome consistent with its flavonoid-rich profile.

Antimicrobial screening added another dimension. The extracts inhibited microbial growth in a concentration-dependent manner, with the largest inhibition zones measuring 15 millimeters against the Gram-positive bacterium Bacillus subtilis and 18 millimeters against the yeast Candida albicans. The authors are careful to frame these results as initial screening evidence rather than definitive antimicrobial potency data, but the pattern aligns with a substantial body of literature showing that plant phenolics, particularly flavonoids, can disrupt microbial membranes and interfere with microbial metabolism. The activity against Candida albicans is especially noteworthy given the clinical challenge posed by fungal infections and the ongoing search for plant-derived antifungal leads.

Perhaps the most pharmacologically intriguing results concerned enzyme inhibition and membrane protection. The extracts suppressed alpha-amylase, the digestive enzyme that breaks down starch into sugars, with the strongest preparation achieving 74.36 percent inhibition and an IC50 of 3.33 milligrams per milliliter. Kinetic analysis suggested an apparent competitive mode of inhibition under the experimental conditions, meaning the extracts’ constituents appear to compete with starch for the enzyme’s active site, a mechanism directly relevant to managing post-meal blood glucose spikes. However, the authors caution that this inhibition pattern requires validation through nonlinear kinetic modeling and independent determination of inhibition constants before firm mechanistic conclusions can be drawn. On the anti-inflammatory front, the extracts stabilized biological membranes, protecting up to 42.02 percent of red blood cells against heat-induced hemolysis, with methanolic extracts generally outperforming ethanolic ones. Because membrane stabilization is considered a plausible in vitro proxy for anti-inflammatory action, this result opens a tentative window onto the extracts’ therapeutic potential.

The researchers are equally candid about the limits of their work, and that transparency is itself scientifically valuable. Only one biological specimen from each flower-color variant was sampled, so the findings describe the particular extracts examined rather than population-level differences between red- and white-flowered E. sideroxylon as a whole. Tree age, season, soil, climate and local growing conditions can all influence phenolic accumulation, and a single tree per form cannot disentangle genetic flower-color effects from environmental noise. The team explicitly recommends broader sampling and complementary analytical approaches, including more rigorous enzyme kinetics, to test whether the observed chemical and biological patterns hold up across populations and to establish their biological significance.

Even with those caveats, the study adds a compelling chapter to the natural products literature surrounding eucalypts, a genus already celebrated for essential oils, polyphenols and antimicrobial compounds. It demonstrates, with technical rigor, that a visible trait like flower color can accompany measurable shifts in leaf chemistry and bioactivity, and it highlights how extraction solvent acts as a powerful lever on both composition and function. For researchers hunting new antioxidants, antifungal agents or alpha-amylase inhibitors, the message is that E. sideroxylon deserves closer attention, and that the red and white forms may offer subtly different chemical toolkits. For the wider public, it is a reminder that the chemistry of a familiar street tree can be far richer, and far more variable, than its appearance suggests.

Subject of Research: Comparative phytochemical profiling and biological activities of red- and white-flowered forms of Eucalyptus sideroxylon

Article Title: Comparative phytochemical profiling and biological activities of red- and white-flowered forms of Eucalyptus sideroxylon (Myrtaceae)

Article References: Comparative phytochemical profiling and biological activities of red- and white-flowered forms of Eucalyptus sideroxylon (Myrtaceae). (n.d.). https://doi.org/10.1007/s44473-026-00273-8

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00273-8

Keywords: Eucalyptus sideroxylon, phytochemical profiling, phenolic compounds, flavonoids, antioxidant activity, antimicrobial activity, alpha-amylase inhibition, anti-inflammatory activity, HPLC-DAD, ATR-FTIR spectroscopy, solvent extraction, Myrtaceae