2025 年 74 巻 10 号 p. 859-878
Abstract: Camellia oleifera seed oil (COSO), a nutritionally rich oil from a key southern Chinese woody crop, has gained significance in food, cosmetic, and pharmaceutical fields. This review summarizes its high-value products, extraction technologies, chemical composition, and health benefits. High-value products include crude COSO and refined COSO, with by-products such as seed meal and shells that yield bioactive compounds for animal feed, fertilizers, and nutraceuticals. Extraction methods range from traditional mechanical pressing and solvent extraction to innovative approaches like supercritical CO2 extraction and enzyme/ultrasound/microwave-assisted techniques. Chemically, COSO features a balanced fatty acid profile dominated by oleic acid (52.13%-86.6%), along with abundant phytosterols, squalene, α-tocopherol, and phenolic compounds, which collectively enhance its oxidative stability and antioxidant activity. Health benefits include antioxidative and anti-inflammatory effects, cardiovascular protection, neuroprotection in Alzheimer's disease, anti-fatigue properties, antimicrobial activity, and osteoporosis prevention via mechanisms like NF-κB signaling modulation. In conclusion, COSO and its by-products offer nutritional, industrial, and therapeutic value, with innovative technologies promoting sustainability. Further research on large-scale optimization and by-product utilization is needed to fully exploit their potential in functional foods and healthcare.
Camellia oleifera, a member of the Theaceae family, has played a vital role as a woody oil crop in Southern China for more than 2,300 years1) , 2) . It is globally recognized as one of the four primary woody edible oil plants, alongside oil palm, olive, and coconut3) . Camellia oleifera seed oil (COSO) , derived from Camellia oleifera seeds (COSs) , is highly prized as a premium edible oil and serves as a vital raw material for the cosmetics and pharmaceutical sectors4) . Owing to its strikingly analogous physicochemical properties and nutrient composition to olive oil, it is frequently referred to as the 〝Oriental Olive Oil〟5) . COSOs exhibit a nutritional profile as a rich source of unsaturated fatty acids, notably oleic acid (ranging from 52.13% to 86.6%) and linoleic acid (ranging from 3.00% to 24.32%) , as well as phytosterols, squalene, α-tocopherol, polyphenols, and various other bioactive compounds2) . Recent research has shed light on the antioxidative, anti-inflammatory, anti-fatigue, and antimicrobial properties of COSOs, as demonstrated in several studies6) , 7) , 8) , 9) . Additionally, COSOs may serve a valuable prophylactic and therapeutic function in addressing cardiovascular diseases, Alzheimer's disease prevention, and osteoporosis10) , 11) , 12) .
While existing reviews extensively catalog its fatty acid composition and health benefits, critical gaps persist in three areas: (1) systematic valorization of underutilized by-products for industrial and nutraceutical applications; (2) comparative analysis of emerging extraction technologies balancing yield, sustainability, and bioactive preservation; and (3) mechanistic insights into COSO's modulation of signaling pathways in chronic diseases. These gaps hinder the translation of COSO's potential into scalable, eco-friendly processes and evidence-based therapeutic strategies.
This review addresses these challenges by synthesizing interdisciplinary advances in green extraction, circular economy frameworks, and multi-omics-driven mechanistic studies. The article critically evaluates various extraction methods, emphasizing novel hybrid techniques that enhance oil quality while enabling protein/polysaccharide recovery from by-products. Furthermore, we elucidate COSO's role in gut microbiota modulation and epigenetic regulation-areas underexplored in prior reviews-supported by recent preclinical and clinical data. By contextualizing COSO within global trends in sustainable functional ingredients and preventive medicine, this work provides a roadmap for maximizing the economic, environmental, and health impacts of Camellia oleifera resources, bridging the divide between traditional applications and modern scientific innovation.
Derived from Camellia oleifera seeds (COSs) , crude Camellia oleifera seed oil (C-COSO) is a natural, multifunctional oil distinguished by its high oleic acid content exceeding 50% which contrasts with traditional edible oils such as sesame, coconut, and safflower oils, which typically contain approximately 30% oleic acid13) . Oleic acid, a monounsaturated fatty acid, is a key nutrient recognized for its anti-inflammatory activities, cardiovascular protective effects, and potential role in supporting cognitive function. Characterized by a mild nutty flavor and light consistency, C-COSO is well-suited for diverse culinary applications, including sautéing, stir-frying, and salad dressing formulations14) , 15) .
Beyond culinary use, C-COSO demonstrates functional properties in cosmetics: its natural antioxidant profile provides protection against ultraviolet (UV) radiation when applied topically16) . From a storage stability perspective, C-COSO mirrors olive oil and outperforms sunflower oil; as a natural additive, it extends the shelf life of sunflower oil by 5%17) . However, its utility as a cooking and salad oil remains regionally limited in certain Asian areas due to its high saponin content, which imparts a bitter taste18) .
2.2 RefinedCamellia oleifera seed oil (R-COSO)Crude Camellia oleifera seed oil (C-COSO) is characterized by elevated concentrations of free fatty acids, saponins, dark pigments, and off-odors impurities that, if unprocessed, can compromise both its quality and consumer acceptability. To meet the stringent requirements for food and cosmetic applications, a systematic refining process is employed to remove these constituents. The refining sequence, comprising degumming, neutralization, bleaching, and deodorization, operates under distinct operational parameters (Fig. 1) 18) .
Schematic diagram of COSO extraction and refining processes*.
*COS: Camellia oleifera seeds; COSM: Camellia oleifera seed meal (COSM) ; COSC: Camellia oleifera seed cake (COSC) ; COSP: Camellia oleifera seed powder (COSP) ; C-COSO: Crude Camellia oleifera seed oil; R-COSO: Refined Camellia oleifera seed oil.
Degumming targets the elimination of phospholipids, trace metals, and mucilaginous substances, which can otherwise precipitate during storage and degrade oil quality, including color and flavor stability19) . This process separates hydratable gums (primarily phospholipids) from the crude oil, yielding degummed oil and a by-product stream (gum or lecithin) . Neutralization, or deacidification, reduces free fatty acid content to below 0.1%, a critical quality standard for refined edible oils, producing neutral oil and soap stock as a by-product. While traditionally focused on color remediation, modern bleaching processes also eliminate a broader spectrum of undesirable compounds, including aldehydes, ketones, peroxides, trace metals, pesticides, and polycyclic aromatic hydrocarbons20) .
Deodorization represents the final refining stage, aiming to produce a bland, stable oil through steam distillation. This step effectively removes volatile components, such as free fatty acids, peroxides, and odoriferous aldehydes/ketones, from the bleached oil, generating deodorized oil and a valuable by-product (deodorizer distillate) 21) . Beyond impurity removal, these refining steps enhance the oil's oxidative stability and nutritional profile, while enabling the recovery of by-products for further valorization.
2.3 Camellia oleifera seed meal (COSM)Camellia oleifera seed meal (COSM) is a fine-textured byproduct generated during the mechanical pressing or conventional organic solvent leaching of Camellia oleifera seeds (COSs) . Characterized by a notable composition, COSM contains 10% saponins, 2% tannins, 12%-18% crude protein, 5% crude fat, and 40% sugars22) , 23) , 24) . As a protein-rich byproduct, it is widely utilized in animal feed, fertilizer production, and biofuel applications25) , 26) , 27) , 28) . Recent investigations have explored its functional potential: Maillard reaction products derived from COSM have been developed into antioxidant-rich flavoring agents29) , while protein hydrolysates from COSM serve as a primary substrate for purifying angiotensin-I-converting enzyme (ACE) inhibitory peptides30) , 31) .
2.4 Camellia oleifera seed cake (COSC)Camellia oleifera seed cake (COSC) is the primary solid residue generated during the mechanical pressing of Camellia oleifera seeds for oil extraction, with annual pro-duction in China reaching approximately 73 million tons32) . Despite its substantial output, COSC has seen limited industrial exploitation, primarily utilized in biofuel production, detergent formulations, animal feed, and organic fertilizers33) , 34) , 35) , 36) . Even after defatting, COSC retains a rich array of bioactive constituents, including amino acid (87.04 g/kg) 37) , polyphenols (29.01 mg GAE/g dw) 38) , crude polysaccharides (1.8%) 39) , saponins (11%-17%) 40) , tannins (1.03%) 41) , and flavonoids (29.01 mg QC/g) 38) .
Recent advancements highlight its potential in functional applications: albumin extracted from COSC proteins has been used as a carrier for lutein-loaded nanoparticles, fostering sustainable utilization of this byproduct42) . Bioactive polysaccharides isolated from COSC, valued for their hypoglycemic, antioxidant, and antitumor activities, are increasingly incorporated into functional food formulations39) , 43) , 44) , 45) . Phenolic extracts from COSC act as natural antioxidants, inhibiting the formation of harmful compounds, such as polar substances, aldehydes, and monoepoxy oleic acids, during high-temperature frying processes38) . Additionally, four oleanane-type triterpenoid saponins identified in COSC have demonstrated potent cytotoxic effects against five human tumor cell lines, namely hepatocellular carcinoma (BEL-7402) , gastric adenocarcinoma (BGC-823) , breast adenocarcinoma (MCF-7) , acute promyelocytic leukemia (HL-60) , and nasopharyngeal carcinoma (KB) , underscoring its therapeutic potential32) .
2.5 Camellia oleifera seed powder (COSP)Camellia oleifera seed powder (COSP) is the granular byproduct generated during COSO production in southern China, with a single county in Guangxi province reportedly yielding approximately 2,000 tons annually46) . Despite its substantial output, COSP is often discarded or used as fuel, releasing harmful particulates and contributing to environmental pollution. Current research focuses on enhancing its sustainable utilization, particularly as a cost-effective, eco-friendly adsorbent for removing hazardous dyes and heavy metal ions from wastewater46) , 47) . Innovative applications include 3D-printed porous materials derived from COSP, which exhibit improved adsorption capacity for methylene blue compared to conventional adsorbents48) .
2.6 Camellia oleifera seed shells (COSS)Camellia oleifera seed shells (COSS) , the hard outer husks of Camellia oleifera seeds (COSs) , represent a significant residual by-product of COSO production. These shells are rich in bioactive compounds, including tea saponin (16%-19%) , tannins (9%-11%) , proteins (2%-4%) , and bioactive polysaccharides (2%-8%) 49) , 50) , 51) . COSS exhibit substantial potential as mushroom bed substrates; a formulation containing 40% COSS and 20% sawdust was shown to promote the growth of Hericium erinaceus, yielding a 29.2% increase in fruiting body production when integrated into a 63% COSS-dominated substrate52) . Commercially, COSS are often blended with other nut shells (e.g., chestnut, walnut) , crushed, and compressed into standardized briquette fuel53) , 54) . As reported in previous studies, COSS exhibits a high calorific value of 19.08 MJ/kg, which is significantly higher than miscanthus grass (17.52 MJ/kg) , bamboo (18.39 MJ/kg) , and Egyptian grass (18.09 MJ/kg) , making it a competitive biomass fuel feedstock55) . From a biochemical perspective, COSS serve as a valuable source for isolating bioactive polysaccharides with antioxidant activity and inhibitory effects against α-glucosidase and α-amylase24) , 56) , 57) , highlighting their utility in functional food and pharmaceutical research.
In southern China, COSO serves as a dominant cooking oil, with over 50% of the region's edible vegetable oil derived from COSs58) . Despite its culinary significance, COSO production faces technical challenges, as outlined in the schematic of extraction and refining processes depicted in Fig. 1. Prior to oil extraction, COSs undergo rigorous cleaning to eliminate impurities such as stems, leaves, shells, dust, sand, metallic contaminants, and moldy particles59) .
A critical preprocessing step involves drying, typically via sun exposure, hot air, or, when necessary, ultrasound/microwave pretreatment, to ensure oil quality. This process is tightly controlled at approximately 60°C to reduce seed moisture content, inhibit microbial growth, and prevent deleterious biochemical reactions59) . Subsequently, dehulling machinery separates the seed shells from kernels, facilitating efficient oil recovery60) . Heat-moisture conditioning follows, wherein kernels are treated at an optimal temperature of 90°C for 30 minutes to maintain a moisture content of 5%-8%, enhancing the release of oil droplets from cellular structures during pressing61) , 62) .
After kernel grinding, COSO is extracted using methods detailed below. Table 1 summarizes extraction yields and optimized parameters for both traditional and innovative extraction techniques, highlighting the balance between efficiency and quality in industrial processing.
Extraction yields of COSO obtained by different technologies.
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Mechanical pressing methods are preferred in vegetable oil production due to their operational simplicity, chemical-free processing, high oil recovery efficiency, and preservation of oil quality attributes. Two primary mechanical pressing techniques are employed: screw pressing (Fig. 2A) and hydraulic pressing (Fig. 2B) . The screw press utilizes a rotating screw axis to perform continuous feeding, crushing, and oil extraction within approximately 1 minute74) . Turbidity generated during this process is mitigated through sedimentation or filtration, ensuring the extracted oil retains its natural nutritional and flavor profiles.
In contrast, hydraulic presses use a liquid medium to transmit pressure (62 MPa applied over 30 minutes) for oil extraction from COSs74) . Compared to solvent extraction, hydraulic systems offer lower capital and operational costs with minimal chemical contamination risks. Typically used at the laboratory scale, hydraulic pressing maintains superior physicochemical properties and sensory quality of COSO75) . Screw pressing, conversely, is better suited for industrial-scale continuous or semi-continuous operations. Jirarattanarangsri et al.63) reported that screw pressing had negligible effects on the acid value and free fatty acid content of extracted COSO. Rakita et al.76) systematically compared cold-pressed and solvent-extracted COSO, revealing that cold-pressed oils exhibited superior preservation of bioactive components. Specifically, cold-pressed oils contained 148% higher α-tocopherol (26.8±2.33 vs 10.8±0.28 mg/kg) and 197% greater γ-tocopherol (547.4±38.5 vs 198.2±15.6 mg/kg) compared to petroleum ether-extracted counterparts. Notably, cold-pressed oils demonstrated enhanced oxidative stability at moderate temperatures (63°C) .
3.2 Solvent extraction (SE)Solvent extraction (SE) represents a conventional technique widely adopted in industrial-scale oil production owing to its economic viability and operational efficiency2) . This method hinges on the ability of chemical solvents to dissolve vegetable oils, enabling extraction from whole seeds. In the context of COSO extraction, solvent selection is a pivotal determinant influencing both oil yield and the nutritional profile of C-COSO79) . In industrial-scale COSO production, hexane is the predominant solvent due to its high extraction efficiency, low boiling point, and regulatory approval for food-grade oil extraction. Other solvents (e.g., methanol, petroleum ether, diethyl ether, chloroform) are primarily used in laboratory research but face restrictions in edible oil applications due to residual toxicity concerns and regulatory limitations80) . Hexane typically achieves 41.30%-44.42% oil yield from COSs under optimized conditions (liquid-solid ratio 8:1 mL/g, 45°C, 2 h) 81) , comparable to its efficiency in soybean (24.28%) 82) and sunflower (22.8%) extraction83) .
However, when compared to mechanical pressing extraction (MPE) , solvent-extracted COSO often exhibits lower quality metrics, including fatty acid composition and natural compound content, primarily due to residual solvent transfer into the oil during processing84) . It is critical to emphasize that organic solvents can introduce undesirable odors, flavors, and chemical toxicity, posing health risks unless the oil undergoes rigorous refining. These limitations underscore the need for careful solvent selection and post-extraction purification to ensure safety and suitability for human consumption2) .
3.3 Supercritical carbon dioxide fluid extraction (SFE-CO2)Supercritical fluid extraction (SFE) is a high-pressure technique that facilitates the separation of target solutes from solid matrices through intimate contact with super-critical fluids, as illustrated in Fig. 385) . Leveraging the gas-like diffusivity and liquid-like density of these fluids, supercritical carbon dioxide (CO2) (a non-toxic, non-flammable, and generally recognized as safe (GRAS) compound) serves as an environmentally benign alternative to conventional toxic organic solvents86) , 87) , 88) . Characterized by excellent dissolving capacity, high diffusivity, low viscosity, non-corrosiveness, and thermostability, CO2 is ideally suited for SFE applications, particularly for heat-sensitive bioactive compounds.
Schematic diagram of COSO extraction by supercritical CO2 extraction method93) .
Compared to traditional extraction methods, SFE-CO2 reduces the need for extensive refining while enhancing oil yield and quality, with minimal chemical residues or contaminants detected in the extracted oil89) , 90) . Fang et al.84) reported that SFE-CO2-extracted COSO exhibited the highest contents of β-sitosterol, squalene, and tocopherol compared to mechanical pressing (MPE) , aqueous enzyme extraction (AEE) , and solvent extraction (SE) , although fatty acid compositions showed no statistically significant differences from soxhlet extraction80) . Under optimized conditions (45°C, 32 MPa, 89.7 min dynamic extraction) , Wang et al.65) achieved a COSO yield of 29.2%, significantly higher than the 25.3% obtained via solvent extraction. Natolino et al.64) further demonstrated a maximum yield of 50.03±0.68% (w/w) at 300 bar and 40°C, highlighting the technique's efficiency. While SFE-CO2 is lauded for its safety, sustainability, and ability to preserve bioactive components, its industrial adoption is constrained by high equipment and operational costs, limiting large-scale implementation91) , 92) .
3.4 Aqueous extraction (AE)Aqueous extraction (AE) emerges as a promising eco-friendly alternative to SE, leveraging water as the extraction medium to solubilize intracellular components and facilitate oil release into the liquid phase, followed by centrifugal separation of the oil fraction79) . C-COSO obtained via AE exhibits superior quality, meeting or even exceeding the national standard for first-grade pressed oil, often obviating the need for subsequent refining processes5) , 94) . Lv et al.66) developed an innovative aqueous protocol using 1.2 g water, 0.1 g sodium chloride, and 8 mg sodium bicarbonate per 10 g of COS slurry, achieving a high oil extraction efficiency of 94.79% and producing a defatted meal with only 3.67% residual oil, characteristics indicative of premium-quality byproducts. This method offers milder, environmentally benign extraction conditions compared to conventional techniques, enhancing its suitability for the comprehensive utilization of co-products95) .
However, the complex multi-layered structure of plant cell walls poses a significant challenge, necessitating the use of at least three types of hydrolytic enzymes to disrupt cellular integrity. This enzymatic requirement increases processing costs, limiting the industrial scalability of AE despite its technical merits96) , 97) .
3.5 Enzyme-assisted aqueous extraction (EAAE)Enzyme-assisted aqueous extraction (EAAE) represents an environmentally friendly oil extraction technology, as illustrated in Fig. 4, wherein specialized enzymes, including protease, cellulase, and pectinase, are integrated into the aqueous extraction process to enhance oil recovery. These enzymes degrade plant cell walls and hydrolyze structural polysaccharides and lipoprotein complexes, facilitating the release of intracellular oils98) . Following enzymatic hydrolysis, the mixture is centrifuged to yield three distinct phases: an upper oil-rich layer, a middle aqueous phase containing dissolved bioactive components, and a lower solid meal residue99) . This three-phase separation enables efficient recovery of COSO alongside valuable co-products such as proteins, polysaccharides, and polyphenols100) .
Schematic diagram of COSO extraction by enzyme-assisted aqueous extraction method.
EAAE offers notable advantages over traditional solvent-based methods: it eliminates the need for organic solvents, operates under mild conditions that reduce energy consumption and preserve heat-sensitive bioactives, and allows precise optimization of extraction parameters through enzyme selection and process control66) . Peng et al.69) reported that a 5-hour hydrolysis using free cellulase and Alcalase enzymes achieved a free oil recovery of 94.14%, demonstrating the technique's high efficiency.
However, the formation of stable oil-in-water emulsions during centrifugation poses a critical challenge to commercial scalability, necessitating additional de-emulsification steps68) . Yang et al.94) developed a novel aqueous extraction protocol involving freeze-thaw treatment of emulsified oil, yielding 89.37% COSO, significantly higher than microwave-assisted aqueous enzymatic extraction (83.05%, p<0.05) and comparable to cold pressing (90.85%) and refined solvent-extracted oil. Despite these advancements, the substantial enzyme consumption in EAAE increases production costs, limiting its practical implementation. Future research will focus on optimizing enzyme formulations and developing efficient emulsion-breaking techniques to overcome these bottlenecks.
3.6 Ultrasound-assisted extraction (UAE)Ultrasonic-assisted extraction (UAE) is an environmentally friendly technique utilizing high-frequency sound waves (20 kHz-10 MHz) to induce cavitation, a process whereby mechanical energy generates and collapses vapor bubbles in the extraction solvent101) . This cavitational effect disrupts plant cell walls, enhancing mass transfer and facilitating the release of intracellular lipids into the solvent phase102) .
Numerous studies have demonstrated that UAE significantly improves COSO yield under optimized conditions: 50 W ultrasonic power, 30°C extraction temperature, 30 minutes treatment time, and a 6:1 (v/w) liquid-to-solid ratio, yielding 85.21% COSO, substantially higher than conventional solvent extraction71) . Mechanistically, ultrasonic waves propagate through the liquid medium, generating cavitation bubbles that collapse violently under localized high temperature and pressure. This produces shock waves and high-speed jets, enhancing solvent penetration into seed cell tissues and accelerating the dissolution of oil bodies via cell wall disruption103) , 104) , 105) .
COSO recovery increases with ultrasonic power: elevating power from 10 to 50 W boosts yield from 46.23% to 85.21%, reflecting stronger cavitational forces71) . Conversely, temperature exerts a biphasic effect: yields peak at 30°C, declining at higher temperatures (30-60°C) due to reduced bubble collapse efficiency, despite increased bubble formation. This highlights the critical role of cavitation intensity in optimizing UAE performance71) .
3.7 Microwave-assisted extraction (MAE)Microwave-assisted extraction (MAE) is an eco-friendly, high-efficiency technique leveraging non-ionizing electromagnetic waves (300 MHz-300 GHz) to induce dielectric heating, which disrupts oilseed cell structures and accelerates the release of intracellular oil bodies106) , 107) . Key parameters governing its extraction efficiency include treatment time, temperature, microwave power, solid-to-liquid ratio, and solvent polarity108) .
This technology enhances COSO yield, reduces extraction duration, and minimizes chemical solvent use72) . Notably, MAE promotes the production of phenolic compounds, potent antioxidants that mitigate lipid peroxidation during COSO storage and thermal processing. Microwave pretreatment of COSs has been shown to increase total carotenes by 52.16%, sterols by 13.27%, and squalene by 10.95%, contributing to the oil's exceptional oxidative stability73) . Mechanistically, microwave energy induces protein denaturation in seed cells, weakening cellular matrices and facilitating oil release during subsequent solvent extraction. Experimental data demonstrate that MAE can elevate COSO yield from 53% to 95% compared to conventional methods, underscoring its efficiency in improving extraction kinetics109) .
While MAE offers notable advantages in efficiency and bioactive preservation, it is not without limitations. The technology requires specialized microwave equipment, leading to higher initial capital investment compared to conventional extraction methods, which may pose challenges for large-scale industrial adoption, particularly in resource-constrained settings. Additionally, although MAE typically employs lower temperatures than traditional thermal techniques, improper optimization of parameters could potentially induce thermal degradation of heat-sensitive phytochemicals, necessitating rigorous process control to maintain oil quality.
Fatty acid composition is a critical quality parameter for oil crops, serving as a key indicator of oxidative stability and governing the nutritional profile of plant oils. These components are fundamental to human physiology, influencing membrane structure, intracellular signaling, transcription factor activity, gene expression, and the biosynthesis of bioactive lipid mediators. The fatty acid profile of COSO exhibits qualitative and quantitative variations attributable to genetic origin, cultivation practices, storage conditions, extraction methods, and analytical techniques.
Table 2 summarizes the fatty acid composition (%) of COSO from diverse geographical regions, revealing saturated fatty acid (SFA) contents ranging from 8.99% to 22.71%, monounsaturated fatty acids (MUFA) from 54.12% to 87.00%, and polyunsaturated fatty acids (PUFA) from 3.10% to 24.55%. Oleic acid (C18:1) , the predominant MUFA, accounts for 52.13% (Hunan) to 86.6% (Tokyo) of total fatty acids, underscoring COSO's predominantly unsaturated nature. Palmitoleic acid (C16:1) is present at low levels (0.07-0.24%) , while linoleic acid (C18:2) varies significantly between regions, with Tokyo cultivars showing 3.00% and Hunan cultivars 24.32%.
Fatty acid composition (%) of COSOs from different geographic regions.
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Unsaturated fatty acids (UFAs) in COSO confer multiple health benefits, including anti-inflammatory effects, blood lipid regulation, delayed atherosclerosis progression, and prevention of hypertension, hyperlipidemia, and other cardiovascular disorders. Regional disparities are evident in SFA composition: palmitic acid (C16:0) ranges from 7.50% (Tokyo) to 17.36% (Hunan) , and stearic acid (C18:0) from 1.08% (Hainan) to 4.13% (Chiang Rai) . Arachidic acid (C20:0) is detected as a trace component in samples from Jiangxi, Tokyo, Hainan, Guangxi, Guangdong, Jiangsu, Hunan, and Chiang Rai.
Genetic and environmental factors significantly influence these variations. He et al.114) reported that fruit ripeness profoundly impacts fatty acid composition: oleic acid peaks mid-ripening before declining, while linoleic and palmitic acids decrease gradually, and stearic acid increases. Drought stress further alters the profile, causing substantial reductions in stearic, oleic, and linolenic acid levels117) , highlighting the interplay between agronomic conditions and lipid biosynthesis.
4.2 Phytosterols and squalenePhytosterols represent critical micronutrients in edible vegetable oils, with compelling evidence supporting their essential role in lowering blood cholesterol levels and reducing cardiovascular disease risk118) . The Food and Agriculture Organization (FAO) recommends that individuals with normal or elevated cholesterol incorporate adequate phytosterol intake into their diets, establishing an acceptable daily intake (ADI) of 0-40 mg/kg body weight119) . Compared to common vegetable oils such as corn, rapeseed, soybean, and sunflower oils, COSO stands out for its remarkably high phytosterol content.
Table 3 summarizes the total phytosterol content of COSO across diverse Chinese regions, ranging from 1,514 to 7,626 mg/kg. Over 100 distinct phytosterol compounds have been identified in COSO, with lanosterol (934.41-1,680.95 mg/kg) prevailing as the major component, followed by β-amyrin (362.10-607.24 mg/kg) , cycloartenol (662.88-1,565.33 mg/kg) , betulin (250.19-480.26 mg/kg) , stigmast-7-en-3-ol (191.37-552.87 mg/kg) , lupeol (306.64-757.75 mg/kg) , and β-sitosterol (229.58-820.22 mg/kg) , collectively accounting for over 95% of total phytosterols. In contrast, stigmasterol (48.36 mg/kg) and campesterol (44.44-120.63 mg/kg) are present in relatively minor quantities115) .
Phytosterols and squalene (mg/kg) of COSO from different geographic regions59) , 115) , 120) .
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Phytosterol composition in COSO exhibits variability influenced by plant genotype, agronomic practices, storage conditions, and extraction methods115) , 121) . These bioactive compounds not only contribute to the oil's nutritional value but also underscore its potential as a functional food ingredient in cholesterol-lowering dietary strategies.
Squalene, a bioactive triterpene compound, serves as a key precursor in the biosynthesis of phytosterols and other steroidal compounds. Extensive in vitro and in vivo studies have highlighted its multifunctional properties, including anticancer, antioxidative, anti-inflammatory activities, skin moisturizing effects, and potential applications in drug delivery systems122) , 123) . In COSO, squalene has been identified as a major bioactive component, with concentrations ranging from 117.5 to 756.38 mg/kg (Table 3) .
Notably, COSO exhibits significantly higher squalene levels compared to conventional vegetable oils: rapeseed oil (34.18 mg/kg) , soybean oil (58.42 mg/kg) , safflower oil (62.27 mg/kg) , sesame oil (9.94 mg/kg) , walnut oil (22.71 mg/kg) , flaxseed oil (27.05 mg/kg) , linseed oil (23.21 mg/kg) , and cottonseed oil (70.95 mg/kg) 124) . This substantial squalene content positions COSO as a valuable botanical source of this bioactive lipid, with promising implications for functional food development and nutraceutical applications.
4.3 Vitamin EVitamin E, a vital lipophilic antioxidant micronutrient, exerts diverse biological effects in the human body and plays a pivotal role in preserving the quality of plant oils during processing and storage by inhibiting lipid oxidation, thereby preventing rancidity and the formation of undesirable off-flavors125) . Comprising tocopherols and tocotrienols, vitamin E occurs naturally in four isomeric forms (α, β, γ, δ) , with α-tocopherol typically exhibiting the highest concentration and biological activity124) , 126) . γ-Tocopherol, conversely, has emerged as a promising anti-inflammatory and anticancer agent, demonstrating efficacy in mitigating mild-to-moderate colon cancer tumor growth and reducing tumor heterogeneity127) .
COSs and their derived oil (COSO) represent valuable industrial sources of vitamin E. Uoonlue et al.80) reported that solvent-extracted COSO contains total vitamin E concentrations ranging from 16.88 to 23.84 mg/100 g, with α-tocopherol as the predominant (nearly exclusive) component. This content significantly surpasses that of other common oils: rice bran oil (9.45 mg/100 g) 80) , palm oil (9.5-13 mg/100 g) 128) , low-phenolic olive oil (14.13 mg/100 g) 129) , and coconut oil (2.90 mg/100 g) 129) . A regional study by Ye et al.130) analyzing COSO from eight locations observed total tocopherol content ranging from 11.23 to 33.87 mg/100 g, with α-tocopherol accounting for ~98% (11.06-33.26 mg/100 g) , and minor contributions from γ-tocopherol (0.18-0.50 mg/100 g) and δ-tocopherol (0.05-0.11 mg/100 g) . These data underscore COSO's status as a rich botanical source of α-tocopherol, positioning it as a valuable industrial source for functional food and nutraceutical applications.
4.4 Phenolic compoundsCOSO exhibits exceptional oxidative stability, attributed to its abundant natural antioxidants, most notably, phenolic compounds. The total phenolic content of COSO ranges from 22.57 to 52.93 mg gallic acid equivalents (GAE) /100 g of oil131) , 132) , with these compounds significantly contributing to its robust antioxidant capacity. Compared to other common plant oils, COSO contains notably higher phenolic levels: corn oil and palm oil exhibit 6.1-9.1 mg GAE/100 g133) , peanut oil 0.57-0.98 mg GAE/100 g134) , rapeseed oil 1.35-1.96 mg GAE/100 g, and safflower oil 4.08 mg GAE/100 g135) , highlighting its superior antioxidant potential.
Using UPLC-MS/MS, Liu et al.136) identified 39 phenolic compounds in COSO, including 22 flavonoids, 1 stilbene, 9 phenolic acids, 2 simple phenols, and 5 other phenols. The ten most abundant components: naringenin (15.47 μg/g) , 3,4-dihydroxyphenyl glycol (11.23 μg/g) , gentisic acid (4.95 μg/g) , hydroxytyrosol (4.60 μg/g) , 7-hydroxy coumarin (2.65 μg/g) , homovanillic acid (2.53 μg/g) , pyrocatechol (2.37 μg/g) , p-hydroxy phenylacetic acid (1.78 μg/g) , p-coumaraldehyde (1.37 μg/g) , and trans-cinnamic acid (1.13 μg/g) , account for over 95% of total phenolic content. Phenolic acids dominate the phenolic profile, comprising 76.2%-90.4% (18.87 μg/g) , followed by catechins (2.1%-9.7%, 1.87-2.78 μg/g) and other flavonoids (4.2%-17.8%) 137) .
In vitro and in vivo studies demonstrate that these phenolic compounds exhibit potent antioxidant activities: they scavenge free radicals (DPPH, ABTS, ･O2-, HO2･) and reactive oxygen species (ROS) , enhance antioxidant enzyme activities (GSH-Px, SOD) , and reduce oxidation product accumulation136) . This biochemical profile underscores the critical role of phenolic compounds in COSO's oxidative stability and its potential as a functional ingredient in antioxidant-rich formulations.
Lipid peroxidation poses significant adverse effects, accelerating food spoilage, damaging cellular membranes, inducing genetic material fragmentation, and increasing disease susceptibility138) . Extensive research has corroborated the potent antioxidant properties of COSs and their derived oil (COSO) , attributed to bioactive components including unsaturated fatty acids, phenolic compounds, saponins, carotenoids, squalene, and vitamins, which collectively confer robust antioxidative and anti-inflammatory activities136) , 139) , 140) . Virgin COSO, in particular, exhibits heightened bioactivity compared to refined oils, as the refining process diminishes its antioxidant component profile141) .
In vitro evaluations of COSO's antioxidant potential using 1,1- diphenyl- 2- pic-rylhydrazyl (DPPH) radical scavenging, lipid peroxidation inhibition (LPO) , and iron-reducing capacity assays (with Trolox® used as standard) revealed substantial activity: EC50 values of 33.48 mg/mL (DPPH) and 2.81 mg/mL (reducing power) , alongside an IC50 of 0.37 mg/mL for LPO inhibition8) . Further in vitro studies demonstrated that COSO mitigates colitis by upregulating antioxidative enzymes (SOD, CAT, GSH-Px) and reducing NO and MDA levels142) . In an acetic acid-induced colitis rat model, daily oral administration of 2 mL/kg COSO for 21 days significantly alleviated colonic damage, increasing serum immunoglobulin G1 while reducing MDA and inflammatory cytokine production in colonic tissue143) . Pre-treatment with COSO (2 mL/kg/day) prior to ketoprofen administration (50 mg/kg/day) in SD rats inhibited cyclooxygenase-2 (COX-2) synthesis, suppressed interleukin-6 (IL-6) and NO production, upregulated heme oxygenase-1 (HO-1) and vascular endothelial growth factor (VEGF) , restored antioxidant system function, and reduced gastrointestinal mucosal oxidative damage144) .
Mechanistically, COSO's bioactive constituents (unsaturated fatty acids, phenolic compounds, and squalene) neutralize free radicals, inhibit lipid peroxidation, and en-hance antioxidative enzyme activity (Fig. 5) . These components may also modulate the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway, reducing downstream pro-inflammatory cytokines (IL-6, tumor necrosis factor-α TNF-α) , IL-1β, IL-22) . By maintaining redox balance, COSO protects against diseases associated with oxidative and inflammatory stress, underscoring its therapeutic potential in preventing and managing chronic conditions.
Schematic diagram of the mechanism of antioxidant and anti-inflammatory effects of COSO. The primary components of COSO can engage in three potential mechanisms to exhibit antioxidant and anti-inflammatory activities. Firstly, bioactive constituents can potentially interfere with the activation of transcription factors, in-cluding AP-1 and NF-κB, thereby preventing the production of downstream products in the NF-κB signaling pathway. Furthermore, they may regulate the growth and repair of epidermal cells through the Ras/Raf/ERK signaling pathway by enhancing the sensitivity of the epidermal growth factor receptor (EGFR) . Additionally, they have the potential to mitigate oxidative stress in tissues and organs by reducing ROS levels and other oxidation products, while simultaneously activating antioxidant enzymes such as SOD, CAT, and GSH6) .
Cardiovascular diseases (CVDs) stand as a primary contributor to global morbidity and mortality. CVDs typically manifest as dyslipidemia, atherosclerosis, hypertension, thromboembolism, arrhythmia, and heart failure, among others. Moderate consumption of dietary vegetable oils, rich in unsaturated fatty acids, is strongly associated with CVD therapy. Studies by Du et al.145) and Gao et al.146) using animal models have reported the effectiveness of COSO in combating CVDs. Preclinical studies indicate that COSO administration in animal models has been associated with increased plasma high-density lipoproteins (HDLs) and decreased levels of total cholesterol (TC) , triglycerides (TGs) , and low-density lipoproteins (LDLs) 147) . In vivo trials in rats demonstrated that COSO, administered at varying dosages (1.5-4.5 g/kg BW) , markedly reduced angiotensin-converting enzyme (ACE) activity in multiple tissues and lowered levels of endothelin, renin, and angiotensin II in the serum. Furthermore, in both long-term and acute administration experiments using spontaneously hyperten-sive rats, COSO exhibited a comparable antihypertensive effect in spontaneously hypertensive rats when compared to olive oil and captopril23) . A recent animal study showed that oral COSO alleviates dyslipidemia in high-fat-fed (HFD) mice by modulating the gene and protein expression of PPARγ, with a particular focus on isoleucine and leucine-mediated regulation of arachidonic acid and steroid biosynthesis metabolism145) . Another animal study demonstrated that COSO supplementation exerted an anti-dyslipidemia effect and mitigated lipid accumulation in HFD mice by inhibiting the mammalian target of rapamycin (mTOR) signaling pathway, leading to the reorganization of gut microbiota, including Alistipes and Dubosiella12) . While these preclinical findings in animal models suggest potential cardiovascular benefits of COSO, confirming these effects and establishing their relevance for human health requires well-designed clinical trials in human populations.
5.3 Prevention of Alzheimer's diseaseAlzheimer's disease (AD) is a progressive neurodegenerative disorder, accounting for 60%-70% of all global dementia cases. It is characterized by disruptions in brain function, cognitive impairment, and neuronal loss148) . Growing evidence suggests that COSO is among the most promising health foods for alleviating AD149) , 150) . Several proposed mechanisms for preventing AD include modulating the microbiota-gut-brain axis, reducing amyloid beta (Aβ) deposition, decreasing Tau protein hyperphosphory-lation, regulating the cholinergic system, reducing oxidative stress, inhibiting apoptosis, and ameliorating inflammation, among others151) , 152) , 153) , 154) . Neuroprotective capabilities improved in AlCl3-induced rats following oleic acid-rich COSO administration, surpas-sing the effects of olive oil treatment. Research data suggested that COSO intake significantly increased the abundance of Ruminococcaceae_UCG014 in gut microbiota, which was positively associated with the reduction of oxidative stress and inflammatory cytokines155) . Moreover, COSO has the potential to ameliorate Aβ25-35-induced memory impairment in mice by modulating in vivo immune cells and brain inflammation via peroxisome proliferator-activated receptors (PPARs) , subsequently influencing gut microbiota and serving as lipid receptors and regulators of lipid metabolism156) .
5.4 Anti-fatigue effectFatigue syndrome has become a significant public concern in modern society. Several factors, such as intensive exercise, chronic insomnia, altitude hypoxia, and drug side effects, can result in severe or prolonged fatigue157) . There is an urgent need to develop foods that can either prevent the onset of fatigue or facilitate the recovery from fatigue-induced damage. COSO has been demonstrated to exhibit anti-fatigue effects and alleviate fatigue symptoms158) , 159) , 160) . Administering COSO at a dosage of 2.0 g/kg body weight for four weeks resulted in reduced body weight in ICR mice and extended their endurance in weight-loaded swimming. The results indicated that ap-propriate COSO dosages have a positive impact on the levels of blood urea nitrogen (BUN) , hepatic glycogen, and blood lactic acid (BLA) . In particular, COSO can enhance hepatic glycogen concentration and inhibit BLA and BUN production during increased exercise load158) .
5.5 Antimicrobial effectCOSO is rich in bioactive compounds, allowing it to function as a natural antimi-crobial agent. Specifically, research has shown that COSO has a stronger inhibitory effect on the growth of gram-negative bacteria in comparison to gram-positive bacteria161) . The results revealed that B. cereus is the least sensitive species, with an MIC of 52.083±18.042 mg/mL, while E. coli is the most sensitive to the antimicrobial effects of COSO, with an MIC of 3.917±3.406 mg/mL8) . It should be noted that this study reported the MIC values specifically for COSO and did not include comparative data with standard antibiotics. Comparable findings were reported in a study conducted by Estevinho and colleagues162) . Nevertheless, the underlying mechanisms of COSO's antimicrobial activity require further investigation in future research.
5.6 Prevention and treatment effect on osteoporosisDue to the aging population in China, the prevalence of osteoporosis is steadily rising. Postmenopausal osteoporosis (PMOP) has emerged as a significant public health concern in China. Due to polymorphisms in estrogen receptor (ER) target genes that contribute to estrogen deficiency, postmenopausal women face an elevated risk of osteoporosis and often exhibit more severe clinical symptoms163) . Numerous studies have indicated that extended consumption of COSO, rich in plant estrogens, may play a role in improving fracture healing in PMOP163) . A study conducted by Fang and colleagues examined the impact of COSO on the secretion of bone metabolic factors, including osteoprotegerin (OPG) and NF-κB ligand (RANKL) , in women of Zhuang nationality in Guangxi, aged from 20 to 80. In particular, a five-year consumption of COSO significantly elevated the serum concentrations of OPG and RANKL in the age group of 55 to 59164) . Li and colleagues conducted a study to investigate the impact of COSO on bone tissue and bone metabolism using an ovariectomized animal model. Administration of 5 mL/kg body weight of COSO over a twelve-week period resulted in increased serum levels of calcium, phosphorus, and estradiol. Furthermore, elevated serum alkaline phosphatase (a key indicator of bone mineralization) was observed along with reduced levels of follicle-stimulating hormone. Additionally, significant improvements in the pathological changes associated with osteoporosis in bone tissue were noted165) . The impact of COSO on preventing and treating PMOP has the potential to enhance patients' quality of life, alleviate the economic burdens on both society and families, and significantly boost the economic benefits derived from COSO resources.
This review of COSO is founded on a comprehensive search that retrieved 165 publications. The results presented in this article suggest that genetic factors, growth conditions, and extraction methods exert significant influence over the yield, phytochemical composition, and physicochemical properties of COSO. In contrast to the traditional chemical solvent extraction method, which poses safety, health, and environmental concerns, various innovative techniques offer alternatives to guarantee the production of safe and high-quality COSO. COSO exhibits a well-balanced fatty acid profile, with oleic acid as the predominant monounsaturated fatty acid (MUFA) , and palmitic and stearic acids as the primary saturated fatty acids (SFAs) . Additionally, it is rich in linoleic acid, the primary polyunsaturated fatty acid (PUFA) . Moreover, COSO is rich in various bioactive compounds, including phytosterols, squalene, α-tocopherol, and polyphenols. This diverse composition underpins the nutritional and functional properties of COSO, offering a plethora of health benefits. Clinical studies have established that COSO has the potential to reduce the incidence of osteoporosis, mitigate the risk of cardiovascular disease through the reduction of total cholesterol and LDL-C levels, alleviate fatigue symptoms, and provide protection against oxidative damage.
As research on COSO and its bioactivities continues to advance, the utilization of COSO as a primary ingredient in diets and dietary supplements is garnering heightened interest within specialized and functional market segments. Nevertheless, current research on COSO remains in its nascent stages. To further explore COSO's development potential in fields like health food and biomedicine, it is imperative to expedite the research, development, and comprehensive utilization of COSO. Firstly, the enhancement of extraction processes should be prioritized. This involves integrating modern extraction techniques and developing more efficient, eco-friendly methods for extracting COSO. These methods should focus on maximizing the preservation of valuable active ingredients in COSO during extraction, while achieving higher oil yields at reduced costs. Secondly, it is essential to intensify research into the health benefits and mechanisms of COSO. Presently, most findings are derived from in vitro experiments, with a dearth of data from animal model experiments or large-scale pop-ulation intervention trials. The next phase should emphasize clinical trials, persistently investigating and substantiating the bioactivities and molecular mechanisms of COSO. These efforts aim to advance the development of COSO-related products suitable for disease prevention and adjuvant therapy. Lastly, promoting the utilization of by-products and facilitating the sustainable development of Camellia oleifera resources is crucial. As a highly valuable woody oilseed resource, the by-products of Camellia oleifera, such as shells, cakes, meals, and flowers, serve as excellent raw materials for fats, proteins, and cellulose. Future research should encompass the comprehensive utilization of various components of Camellia oleifera to investigate their nutritional attributes and bioactivities. This endeavor will contribute to mitigating pollution associated with COSO processing by-products and unlocking innovative pathways for the high-value utilization of by-products from food processing.
The authors declare no conflicts of interest.
This research was funded by the Wenzhou Science and Technology Special Envoy Program, grant number X2028303 and the scientific research fund of Zhejiang provincial education department, grant number Y202352748.
The author would like to express sincere gratitude to the Zhejiang Key Laboratory of Agri-food Resources and High-value Utilization at Wenzhou Vocational College of Science & Technology for their invaluable support and resources throughout the completion of this review.
