Phytochemical Properties and Biological Activities of Quercus Species

The genus Quercus encompasses over 600 species of oaks distributed across temperate and tropical regions, whose leaves, bark and acorns are rich reservoirs of bioactive phytochemicals. Prominent among these are phenolic compounds—including simple phenolic acids, flavonoids and complex tannins—together with triterpenoids, sterols and volatile organic constituents. Extraction methods such as ultrasound‐ and microwave‐assisted techniques have been widely adopted to optimise recovery of these compounds, which exhibit diverse biological activities. In vitro and in vivo studies report potent antioxidant capacity by free‐radical scavenging and ferric‐reducing assays, broad‐spectrum antimicrobial effects against Gram‐positive and Gram‐negative pathogens, and enzyme‐inhibitory properties targeting α-glucosidase, tyrosinase and acetylcholinesterase. Thermal processing of acorns, notably roasting, modulates phenolic profiles and sensory attributes, while enriched extracts from oak cups demonstrate hypoglycaemic and lipid-modulating effects in diabetic models. Collectively, these findings underscore the global significance of Quercus species as sources of natural agents for functional foods, nutraceuticals and pharmaceutical leads, and highlight the need for standardised extraction protocols, comprehensive phytochemical profiling and mechanistic studies to support their practical applications.

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Investigations into bark extracts of Quercus dalechampii and Q. frainetto have employed microwave- and ultrasound-assisted extraction to yield high phenolic and tannin contents, with UPLC-PDA analysis revealing gallic acid, catechin, taxifolin and related compounds. These extracts exhibit moderate antibacterial activity against methicillin-resistant Staphylococcus aureus, α-glucosidase inhibition and cytotoxic effects on cultured cell lines, illustrating their multifunctional bioactivity.

A complementary study on Northern red oak (Quercus rubra) seeds evaluated the impact of roasting at various temperatures on polyphenol content and antioxidant potential. Roasting above 135 °C reduced total phenolics while increasing Maillard-derived melanoidins; both unroasted and mildly roasted seeds retained strong DPPH scavenging and ferric-reducing power, suggesting optimised thermal treatments can balance sensory properties with health-promoting activities.

Further work on Q. rubra bark compares aqueous and ethanolic extracts obtained by ultrasonic- and microwave-assisted methods. Total phenolic and tannin contents varied with technique, and all extracts demonstrated significant antioxidant, anti-glucosidase and anti-tyrosinase activities. Notably, microwave-derived extracts showed enhanced antibacterial effects against Staphylococcus aureus and Candida spp., with inhibition of biofilm formation on clinical isolates.

Phytochemical Properties and Biological Activities of Quercus Species publication trend

The graph below shows the total number of articles in phytochemical properties and biological activities of quercus species across all publications each year (not limited to Nature Index journals).

Technical terms

Phenolic compounds: Plant secondary metabolites bearing one or more hydroxyl groups on an aromatic ring, known for antioxidant and enzyme-modulatory activities.

Tannins: High-molecular-weight polyphenols that precipitate proteins, contributing to astringency and antimicrobial effects.

Flavonoids: A class of polyphenols with C6-C3-C6 structure, associated with anti-inflammatory and free-radical-scavenging properties.

Microwave-assisted extraction: Technique using microwave energy to heat solvent-sample mixtures, improving yield and speed of phytochemical recovery.

Ultrasound-assisted extraction: Use of acoustic cavitation to disrupt plant matrices and enhance release of bioactive compounds.

DPPH assay: Spectrophotometric method that measures antioxidant capacity by reduction of the DPPH radical, indicated by a change in absorbance.

UPLC-PDA: Ultra-performance liquid chromatography with photodiode array detection, enabling separation and quantification of complex phytochemical profiles.

α-Glucosidase: Enzyme that hydrolyses carbohydrates to glucose; its inhibition can moderate postprandial blood sugar excursions.

References

1. Potential Use of Quercus dalechampii Ten. and Q. frainetto Ten. Barks Extracts as Antimicrobial, Enzyme Inhibitory, Antioxidant and Cytotoxic Agents. Pharmaceutics (2023).
2. Bioactive Compounds, Antioxidant Activity and Sensory Properties of Northern Red Oak (Quercus rubra L., syn. Q. borealis F. Michx) Seeds Affected by Roasting Conditions. Molecules (2023).
3. A Comprehensive Review of Phytochemistry and Biological Activities of Quercus Species. Forests (2020).
4. Biological Activity of Bark Extracts from Northern Red Oak (Quercus rubra L.): An Antioxidant, Antimicrobial and Enzymatic Inhibitory Evaluation. Plants (2022).