Common Methods and Experimental Design for Evaluating Antioxidant Activity of Plant Extracts
Common Methods and Experimental Design for Evaluating Antioxidant Activity of Plant Extracts
Polyphenols, flavonoids, phenolic acids, anthocyanins, proanthocyanidins, terpenoids, alkaloids, polysaccharides, and other components in plant extracts may all contribute to antioxidant activity. Evaluation of antioxidant activity should not rely on a single assay. Instead, free radical scavenging, reducing capacity, peroxyl radical absorbance, cellular oxidative stress assays, and total phenol/total flavonoid analysis should be combined according to sample composition, solubility, reaction mechanism, and application scenario.
Keywords: plant extracts; antioxidant activity; DPPH; ABTS; FRAP; ORAC; HORAC; CUPRAC; total phenols; total flavonoids; oxidative stress
1 Basic Logic of Antioxidant Evaluation in Plant Extracts
1.1 Sources of Antioxidant Activity
(1) Hydrogen-donating ability of phenolic hydroxyl groups
Plant polyphenols often contain multiple phenolic hydroxyl groups, which can donate hydrogen atoms or electrons to free radicals and convert them into relatively stable structures. The number, position, conjugated structure, and substituent type of phenolic hydroxyl groups affect antioxidant efficiency.
(2) Electron transfer capacity
Some plant components can reduce oxidative probes or metal ions through electron transfer, showing strong reducing power. FRAP, CUPRAC, and total reducing power assays mainly reflect this type of activity.
(3) Metal ion chelating ability
Certain flavonoids, phenolic acids, and polysaccharides can chelate metal ions such as iron and copper, thereby reducing metal-catalyzed free radical generation. This mechanism differs from direct free radical scavenging and has practical significance in lipid oxidation and cellular oxidative stress.
(4) Regulatory effects in biological systems
In cell or animal models, plant extracts may exert antioxidant effects by regulating antioxidant defense systems such as Nrf2, HO-1, SOD, CAT, GPx, and GSH. These effects cannot be fully explained by chemical assays such as DPPH or FRAP, and cellular-level or biological endpoint evaluations are required.
1.2 Principles for Method Selection
(1) Mechanistic complementarity
DPPH and ABTS mainly evaluate free radical scavenging capacity; FRAP and CUPRAC mainly evaluate reducing capacity; ORAC emphasizes peroxyl radical absorbance capacity; HORAC is more focused on hydroxyl radical-related antioxidant capacity; TBARS or lipid peroxidation models are closer to oxidation processes in foods and biological membranes. Different methods reflect different antioxidant dimensions and should not be used interchangeably.
(2) Sample compatibility
Plant extracts may be water extracts, alcohol extracts, ethyl acetate fractions, n-butanol fractions, polysaccharide fractions, or polyphenol-enriched fractions. Hydrophilic samples are more suitable for ABTS, FRAP, ORAC, and total phenol assays; alcohol-soluble or moderately polar components are more suitable for DPPH, ABTS, CUPRAC, and HPLC component analysis.
(3) Result comparability
Antioxidant results are often affected by extraction solvent, sample concentration, reaction time, detection wavelength, standard selection, and calculation method. When comparing results between laboratories, method conditions should be clearly specified rather than only comparing IC50 or Trolox equivalent values.
2 Sample Preparation and Pretreatment
2.1 Extraction Methods
(1) Water extraction
Water extracts are usually rich in polysaccharides, some phenolic acids, glycosidic flavonoids, and water-soluble anthocyanins. These samples are suitable for ABTS, FRAP, ORAC, total phenol assays, and cell experiments. However, they may react insufficiently in the DPPH system due to poor solubility.
(2) Alcohol extraction
Ethanol, methanol, or their aqueous solutions are commonly used to extract polyphenols, flavonoids, proanthocyanidins, phenolic acids, and some terpenoids. Alcohol extracts are generally suitable for DPPH, ABTS, FRAP, CUPRAC, and HPLC component analysis.
(3) Fractionated extraction
Fractionation with petroleum ether, ethyl acetate, n-butanol, and water can separate components of different polarity. The ethyl acetate fraction often enriches certain phenolic acids and flavonoid aglycones; the n-butanol fraction often enriches flavonoid glycosides and saponins; the aqueous phase may be rich in polysaccharides and inorganic salts.
2.2 Sample Dissolution and Background Control
(1) Solvent selection
Samples should be completely dissolved before entering the assay system. DMSO, methanol, ethanol, water, or buffer may be used as solvents, but the final concentration must not interfere with color development reactions or cell viability. In cell experiments, the final DMSO concentration should be strictly controlled, and solvent controls should be included.
(2) Turbidity control
Proteins, polysaccharides, pigments, and fine particles in plant extracts may increase turbidity and affect absorbance. Before detection, centrifugation, filtration, or appropriate dilution may be used to reduce background interference.
(3) Color background correction
Anthocyanins, chlorophylls, carotenoids, and dark-colored polyphenol extracts have intrinsic absorption peaks, which may interfere with colorimetric results such as DPPH, ABTS, and FRAP. A sample blank should be included, namely “sample + solvent/buffer without the colored free radical or reaction probe.”
2.3 Concentration Gradient
(1) Linear range
A preliminary experiment should be performed to determine the concentration range in which the sample shows a linear response. Excessively high sample concentrations may cause reaction plateauing, color masking, or precipitation; excessively low concentrations may fail to generate stable signals.
(2) IC50 calculation
Free radical scavenging assays such as DPPH and ABTS often calculate IC50, which is the sample concentration required to achieve 50% scavenging. A lower IC50 generally indicates stronger scavenging capacity, provided that curve fitting is reliable and concentration units are consistent.
(3) Standard conversion
Trolox, ascorbic acid, gallic acid, rutin, and quercetin are commonly used as positive controls or standards for equivalent conversion. Equivalent values obtained using different standards should not be directly mixed.
3 DPPH Free Radical Scavenging Assay
3.1 Detection Principle
DPPH is a stable nitrogen free radical. It appears purple in methanol or ethanol and has a characteristic absorption near 517 nm. Antioxidants can donate hydrogen atoms or electrons to DPPH, causing the color to fade. The decrease in absorbance can be used to calculate the free radical scavenging rate.
3.2 Applicable Scope
(1) Suitable samples
The DPPH assay is suitable for evaluating alcohol-soluble or moderately polar plant extracts, such as fractions enriched in flavonoids, phenolic acids, proanthocyanidins, and some terpenoids. It is commonly used for ethanol extracts, methanol extracts, and ethyl acetate fractions.
(2) Unsuitable samples
Highly water-soluble polysaccharide samples, turbid samples, or very dark-colored samples may not be suitable for direct DPPH testing. If the sample cannot fully contact DPPH, antioxidant capacity may be underestimated.
(3) Typical applications
DPPH is commonly used for preliminary screening of plant extracts, comparison of fractionated extracts, ranking of antioxidant activity, and correlation analysis with polyphenol content.
3.3 Experimental Key Points
(1) Operation protected from light
DPPH is light-sensitive, so the reagent should be stored and reacted away from light. Reaction time should be kept consistent during detection to avoid errors caused by natural free radical decay.
(2) Reaction time
Different samples react with DPPH at different rates. Some polyphenols react rapidly, while some polymeric polyphenols or complex extracts react more slowly. Endpoint time should be determined through time-course experiments.
(3) Blank settings
At minimum, a DPPH blank, sample blank, and solvent blank should be included. For deeply colored samples, intrinsic absorbance must be subtracted; otherwise, the scavenging rate may be overestimated or underestimated.
4 ABTS Radical Cation Scavenging Assay
4.1 Detection Principle
ABTS is oxidized to form the blue-green ABTS⁺ radical cation, which has strong absorption near 734 nm. Antioxidants can decolorize ABTS⁺, and the decrease in absorbance reflects free radical scavenging capacity.
4.2 Method Characteristics
(1) Good sample compatibility
Compared with DPPH, the ABTS system is more friendly to water-soluble samples and can also be used for some lipophilic components. Water extracts, alcohol extracts, polyphenol fractions, and polysaccharide fractions can all be tested using this method.
(2) High sensitivity
The ABTS assay responds rapidly and is suitable for batch testing and comparison between different samples. Because its detection wavelength is longer, color interference from some samples is lower than that in the DPPH assay, but sample blanks are still required for dark anthocyanin samples.
(3) Common expression forms
ABTS results are often expressed as scavenging rate, IC50, or Trolox equivalent antioxidant capacity. For comparison of foods or plant extracts, Trolox equivalents are more convenient for cross-sample analysis.
4.3 Experimental Key Points
(1) Preparation of radical working solution
ABTS usually needs to react with an oxidant to generate ABTS⁺ and should be diluted to an appropriate absorbance before use. An excessively high working solution concentration reduces sensitivity, while an excessively low concentration affects repeatability.
(2) Reaction system pH
ABTS reactions are relatively less affected by pH, but different buffer systems may still alter the ionization state of antioxidants. A unified system should be used when comparing samples.
(3) Standard curve
When using Trolox to establish the standard curve, the sample response should fall within the linear range. ABTS⁺ working solutions from different batches should be recalibrated.
5 FRAP Ferric Reducing Antioxidant Power Assay
5.1 Detection Principle
The FRAP assay is based on the reduction of Fe³⁺-TPTZ to Fe²⁺-TPTZ by antioxidants, producing a blue complex detected near 593 nm. Increased absorbance indicates enhanced reducing capacity of the sample.
5.2 Method Positioning
(1) Reflecting reducing capacity
FRAP is not a free radical scavenging assay, but an evaluation of metal ion reducing capacity. Its results are more suitable for indicating electron-donating ability and reducing potential.
(2) Suitable for polyphenol samples
Samples rich in phenolic acids, flavonoids, anthocyanins, and proanthocyanidins often show high FRAP values. Total phenol content is usually correlated to some extent with FRAP results.
(3) Limitations
FRAP reactions are performed under acidic conditions and may not represent antioxidant behavior at physiological pH. Some thiol compounds, slow-reacting antioxidants, or lipophilic components may show insufficient response in the FRAP system.
5.3 Experimental Key Points
(1) Freshness of reagents
FRAP working solution is usually composed of TPTZ, ferric salt, and acidic buffer. It should be freshly prepared or used within a short period. TPTZ dissolution and Fe³⁺ stability can affect results.
(2) Temperature control
The FRAP reaction is temperature-sensitive. Consistent incubation temperature and reaction time are recommended. During batch sample testing, reaction time differences between wells should be avoided.
(3) Result expression
FRAP results can be expressed as FeSO₄ equivalents or Trolox equivalents. When comparing with DPPH and ABTS results, it should be stated that FRAP reflects reducing power rather than free radical scavenging rate.
6 CUPRAC Cupric Ion Reducing Capacity Assay
6.1 Detection Principle
The CUPRAC assay uses antioxidants to reduce the Cu²⁺-neocuproine system to a Cu⁺ complex, producing absorbance near 450 nm. This method can be used to evaluate reducing capacity under near-neutral conditions.
6.2 Method Characteristics
(1) Mild pH conditions
Unlike the acidic FRAP system, CUPRAC often reacts under near-neutral conditions, making it more suitable for evaluating the reducing capacity of some biological samples and complex plant extracts.
(2) Broad applicability to components
CUPRAC responds to polyphenols, vitamin C, thiols, and some lipophilic antioxidants, and can be used as a complementary method to FRAP.
(3) Result interpretation
CUPRAC is still an electron transfer-based method and cannot directly represent free radical scavenging capacity or intracellular antioxidant effects. Its results should be interpreted together with DPPH, ABTS, ORAC, or cell assays.
7 ORAC and HORAC Fluorescence-Based Antioxidant Evaluation
7.1 ORAC Assay
(1) Detection principle
The ORAC assay usually uses AAPH to generate peroxyl radicals and fluorescein as the fluorescent probe. Free radicals gradually quench fluorescence, while antioxidants delay fluorescence decay. The area under the fluorescence decay curve is used to evaluate the peroxyl radical absorbance capacity of the sample.
(2) Method characteristics
ORAC is not a single-time-point absorbance assay, but is based on a fluorescence decay curve. It reflects both the reaction intensity and reaction duration of antioxidants.
(3) Applicable scenarios
ORAC has high reference value in food, nutrition, and functional component evaluation, especially for assessing the sustained peroxyl radical scavenging capacity of plant extracts.
7.2 HORAC Assay
(1) Detection positioning
HORAC is mainly used to evaluate the inhibitory ability of samples against hydroxyl radical-related oxidation processes. Hydroxyl radicals are highly reactive and are often associated with metal-catalyzed oxidation and biomolecular damage.
(2) Suitable samples
Plant extracts rich in polyphenols, flavonoids, phenolic acids, polysaccharides, or metal-chelating components can be evaluated by HORAC to supplement oxidative mechanisms not covered by DPPH, ABTS, and FRAP.
(3) Result interpretation
HORAC results should not be simply equated with total antioxidant capacity. Instead, they should be used as a supplementary indicator for hydroxyl radical-related antioxidant dimensions.
7.3 Experimental Key Points
(1) Fluorescence background control
Plant extracts themselves may exhibit fluorescence or fluorescence quenching ability. Sample blanks and probe blanks should be included.
(2) Curve analysis
ORAC results depend on area-under-the-curve calculation. Data acquisition time should be long enough to cover the fluorescence decay process. If the sample concentration is too high, the curve may remain unchanged for too long, affecting linear analysis.
(3) Trolox standard curve
ORAC results are usually expressed as Trolox equivalents. A standard curve should be established for each experiment, and the sample dilution factor should fall within the linear range.
8 Lipid Peroxidation Inhibition and TBARS Assay
8.1 Detection Principle
Reactive aldehydes such as malondialdehyde can be generated during lipid oxidation. The TBARS assay uses thiobarbituric acid to react with malondialdehyde and generate colored products, thereby evaluating lipid peroxidation levels. If a plant extract reduces the TBARS signal, it indicates potential inhibition of lipid oxidation.
8.2 Applicable Scenarios
(1) Food lipid oxidation
This method is suitable for evaluating the antioxidant protective effects of plant extracts in oils, meat products, dairy products, nuts, vegetable oil emulsions, and functional food systems.
(2) Biomembrane oxidation models
In cells, tissue homogenates, or liposome models, TBARS can be used to evaluate oxidative damage. Plant extracts can be used as intervention factors to observe their inhibitory effect on lipid peroxidation.
(3) Complementarity with chemical free radical assays
Samples with strong DPPH or ABTS activity may not necessarily show strong antioxidant activity in lipid systems. Lipid peroxidation models better reflect sample performance in actual food or biomembrane environments.
8.3 Precautions
(1) Limited specificity
The TBARS assay does not detect only malondialdehyde; other aldehydes or reactive substances may also participate in color development. Therefore, results should be described as TBARS levels or MDA equivalents rather than being absolutely equivalent to malondialdehyde content.
(2) Color interference from samples
Dark-colored plant extracts may interfere with absorbance readings. If necessary, extraction, blank correction, or HPLC detection of MDA derivatives can be used.
(3) Control of reaction conditions
Heating time, acidity, and TBA concentration affect results. Conditions should be kept consistent across experimental batches.
9 Relationship Between Total Phenols, Total Flavonoids, and Antioxidant Activity
9.1 Total Phenol Determination
(1) Folin-Ciocalteu method
This method is based on the reduction of Folin reagent by reducing substances in the sample, and total phenol content is often expressed as gallic acid equivalents. Total phenol content is often correlated with DPPH, ABTS, FRAP, and similar results.
(2) Result interpretation
The Folin-Ciocalteu method is not strictly phenol-specific. Ascorbic acid, reducing sugars, proteins, and other reducing substances may also contribute to the signal. Therefore, total phenol results should be used as auxiliary indicators.
(3) Application value
In plant extract screening, total phenol determination can help determine whether antioxidant activity is mainly contributed by polyphenols and can be used to compare different extraction solvents or fractions.
9.2 Total Flavonoid Determination
(1) Aluminum salt colorimetric method
Flavonoids can form complexes with aluminum ions and are detected by absorbance at specific wavelengths. Results are often expressed as quercetin, rutin, or catechin equivalents.
(2) Method limitations
Different flavonoid structures have different complexing abilities with aluminum ions. Flavonoid glycosides, flavonols, and flavanols show substantial response differences. Therefore, total flavonoid results cannot directly represent the true total amount of all flavonoids.
(3) Relationship with antioxidant activity
Samples with higher flavonoid content generally have stronger antioxidant potential, but activity also depends on structural type, substituents, glycosylation status, and sample matrix.
10 Cellular-Level Antioxidant Evaluation
10.1 DCFH-DA Cellular ROS Detection
(1) Detection principle
DCFH-DA enters cells and is hydrolyzed by esterases to DCFH, which is further oxidized by ROS to fluorescent DCF. Increased fluorescence reflects elevated intracellular oxidative levels.
(2) Experimental design
Common oxidative inducers include H₂O₂, tert-butyl hydroperoxide, AAPH, or high-glucose/inflammatory stimulation. Plant extracts can be used for pretreatment or co-treatment to observe their inhibitory effect on ROS elevation.
(3) Result interpretation
DCFH-DA responds to multiple oxidants and has limited specificity. Results should be interpreted together with cell viability, antioxidant enzyme activity, and oxidative damage indicators.
10.2 Antioxidant Enzyme Activity
(1) SOD
SOD catalyzes the dismutation of superoxide anions and is an important enzyme in cellular antioxidant defense. If plant extracts increase SOD activity, this may indicate enhanced intracellular antioxidant defense.
(2) CAT
CAT decomposes hydrogen peroxide and reduces H₂O₂ accumulation. Combined detection with SOD can better explain the oxidant removal chain.
(3) GPx and GSH
GPx depends on glutathione to participate in peroxide reduction. The GSH/GSSG ratio is an important indicator for evaluating cellular redox status.
10.3 Oxidative Damage Endpoints
(1) Lipid peroxidation
Increased MDA or TBARS levels indicate enhanced lipid oxidative damage. If plant extracts reduce these indicators, they may have membrane lipid-protective effects.
(2) Protein oxidation
Protein carbonyl levels can reflect protein oxidative damage. For cell or tissue samples, this indicator can supplement ROS detection.
(3) DNA oxidative damage
Indicators such as 8-OHdG can be used to evaluate DNA oxidative damage. If studying the cytoprotective effects of plant extracts, this can be used as one of the mechanistic endpoints.
11 Data Expression and Result Interpretation
11.1 Common Expression Methods
DPPH and ABTS are usually expressed as scavenging rate, IC50, or Trolox equivalents. FRAP can be expressed as FeSO₄ equivalents or Trolox equivalents. CUPRAC is often expressed as Trolox equivalents or absorbance change. ORAC is usually calculated using Trolox equivalents and area under the curve. TBARS is often expressed as MDA equivalents or inhibition rate. Total phenols are mostly expressed as gallic acid equivalents. Total flavonoids may be expressed as quercetin equivalents or rutin equivalents.
11.2 Correlation Analysis
(1) Total phenols and antioxidant results
Total phenol content in plant extracts is often positively correlated with DPPH, ABTS, and FRAP results, but this is not absolute. Polysaccharides, vitamin C, pigments, and other reducing components may also affect results.
(2) Differences between methods
Some samples may show weak DPPH activity but strong ABTS activity, which may be related to sample solubility or the reaction system. Strong FRAP but weak ORAC activity may indicate strong electron transfer capacity but limited peroxyl radical trapping ability.
(3) Correspondence between components and activity
If the active substance basis needs to be clarified, HPLC, LC-MS, fractionated purification, and activity-guided tracking should be further combined rather than inferring component contributions only from total antioxidant results.
12 Reagent and Assay Product Selection for Antioxidant Activity Evaluation
12.1 Common Products for Antioxidant Evaluation of Plant Extracts
Method Module | Cat. No. | Product Name | CAS No. | Grade / Specification | Role in the System / Applicable Evaluation Direction |
DPPH free radical scavenging assay | 1,1-Diphenyl-2-picrylhydrazyl Free Radical (DPPH) | 1898-66-4 | ≥95% | Stable free radical probe; determination of DPPH free radical scavenging capacity of plant extracts | |
DPPH free radical scavenging assay | 1,1-Diphenyl-2-picrylhydrazyl Free Radical (DPPH) | 1898-66-4 | ≥97% | High-purity DPPH free radical reagent; establishment of standard DPPH assay systems and antioxidant screening of samples | |
DPPH free radical scavenging assay | DPPH | 1898-66-4 | Moligand™, 10 mM in DMSO | Solution-type DPPH reagent; small-volume reactions, methodological controls, and extracellular antioxidant screening | |
DPPH free radical scavenging assay | 2,2-Diphenyl-1-picrylhydrazyl (contains 10-20% Benzene) | 1898-66-4 | ≥97%(HPLC) | DPPH-related radical reagent; DPPH free radical scavenging experiments; solvent background should be considered | |
DPPH free radical scavenging assay | DPPH Free Radical Scavenging Assay Kit (Micro Method) |
| BioReagent | Micro method for detecting DPPH scavenging rate; preliminary antioxidant screening of multiple plant extract samples | |
DPPH free radical scavenging assay | DPPH Free Radical Scavenging Assay Kit (Colorimetric Method) |
| BioReagent | Colorimetric method for detecting DPPH scavenging rate; routine spectrophotometer platforms and batch sample detection | |
DPPH free radical scavenging assay | Total Antioxidant Capacity (T-AOC) Assay Kit (DPPH, Micro Method) |
| BioReagent | Evaluation of total antioxidant capacity based on the DPPH system; T-AOC detection in plant extracts, food samples, and fermentation samples | |
ABTS radical scavenging assay | ABTS diammonium salt | 30931-67-0 | Moligand™, 10 mM in DMSO | Reaction substrate for ABTS radical cation generation; determination of ABTS radical scavenging capacity | |
ABTS radical scavenging assay | ABTS Solution | 28752-68-3 | pH3.5-5.0 | ABTS reaction solution; establishment of ABTS color development systems and antioxidant capacity comparison | |
ABTS radical scavenging assay | ABTS Free Radical Scavenging Capacity Assay Kit (Micro Method) |
| BioReagent | Micro method for detecting ABTS scavenging capacity; antioxidant evaluation of water extracts, alcohol extracts, and polyphenol samples | |
ABTS radical scavenging assay | Total Antioxidant Capacity (T-AOC) Assay Kit (ABTS) |
| BioReagent | Evaluation of total antioxidant capacity by ABTS method; T-AOC detection in plant extracts, food samples, and biological samples | |
FRAP ferric reducing assay | 2,4,6-Tris(2-pyridyl)-s-triazine（TPTZ） | 3682-35-7 | ≥99% | Fe³⁺-TPTZ chromogenic ligand; determination of ferric reducing antioxidant power | |
FRAP ferric reducing assay | Total Antioxidant Capacity Assay Kit with FRAP method |
| BioReagent | Detection of total antioxidant capacity by FRAP method; reducing capacity evaluation of plant polyphenol, flavonoid, and phenolic acid extracts | |
CUPRAC cupric ion reducing assay | Neocuproine | 484-11-7 | ≥98% | Cu⁺ complex chromogenic reagent; determination of CUPRAC cupric ion reducing capacity | |
ORAC/HORAC fluorescence assay | Oxygen Radical Antioxidant Capacity (ORAC) Assay Kit (Fluorometric Method) |
| BioReagent | Fluorescence-based evaluation of peroxyl radical absorbance capacity; dynamic antioxidant capacity evaluation of plant extracts and functional food assessment | |
ORAC/HORAC fluorescence assay | Hydroxyl Radical Antioxidant Capacity (HORAC) Assay Kit (Fluorometric Method) |
| BioReagent | Detection of hydroxyl radical antioxidant capacity; antioxidant evaluation related to hydroxyl radical scavenging | |
ORAC/HORAC fluorescence assay | 2,2-Azobis(2-methylpropylimidamide) dihydrochloride (AAPH) | 2997-92-4 | ≥97% | Generates peroxyl radicals; ORAC experiments, lipid oxidation models, and oxidative induction systems | |
ORAC/HORAC fluorescence assay | Fluorescein sodium salt | 518-47-8 | AR | ORAC fluorescence decay probe; fluorescence detection system for ORAC assay | |
ORAC/HORAC fluorescence assay | Fluorescein sodium salt | 518-47-8 | ≥70% | Fluorescent probe; ORAC assay and fluorescence-based free radical absorbance capacity evaluation | |
ORAC/HORAC fluorescence assay | Uranine AP (C.I. 45350) | 518-47-8 | concentrated for the examination of subterranean waters | Fluorescein-type probe source; purity suitability should be confirmed for antioxidant assays | |
Cellular oxidative stress evaluation | 2',7'-Dichlorodihydrofluorescein diacetate(DCFH-DA) | 4091-99-0 | ≥97% | Intracellular ROS fluorescent probe; evaluation of cellular antioxidant protective effects of plant extracts | |
Cellular oxidative stress evaluation | tert-Butyl hydroperoxide solution | 75-91-2 | 70% in H2O | Aqueous oxidative damage inducer; establishment of cellular oxidative stress models and evaluation of extract protection | |
Cellular oxidative stress evaluation | tert-Butyl hydroperoxide solution | 75-91-2 | 5.0-6.0 M in decane | Lipophilic oxidative inducer; lipid systems or specific organic-phase oxidation models | |
Antioxidant standards and positive controls | (R)-Trolox | 53101-49-8 | Moligand™, 10 mM in DMSO | Trolox standard; equivalent conversion for ABTS, FRAP, ORAC, and CUPRAC | |
Antioxidant standards and positive controls | (S)-Trolox | 53174-06-4 | Moligand™, 10 mM in DMSO | Trolox isomer standard; methodological control and antioxidant standard curve | |
Antioxidant standards and positive controls | Quercetin | 117-39-5 | Moligand™, 10mM in DMSO | Flavonoid standard or positive control; positive control for DPPH, ABTS, FRAP, and other antioxidant experiments | |
Antioxidant standards and positive controls | Quercetin | 117-39-5 | Moligand™, analytical standard, ≥98.5% | High-purity flavonoid standard; HPLC analysis, total flavonoid standard curves, antioxidant controls | |
Antioxidant standards and positive controls | Quercetin | 117-39-5 | Moligand™, ≥95% | Flavonoid antioxidant control; positive control for DPPH, ABTS, FRAP, and other antioxidant experiments | |
Antioxidant standards and positive controls | Quercetin | 117-39-5 |
| Evaluation of plant flavonoid content and antioxidant activity | |
Total phenol and total flavonoid determination | Gallic acid | 149-91-7 | Moligand™, 10mM in DMSO | Total phenol standard; standard curve for Folin-Ciocalteu assay and correlation analysis between total phenols and antioxidant activity | |
Total phenol and total flavonoid determination | Gallic acid | 149-91-7 | Moligand™, ≥99% | High-purity total phenol standard; determination of total phenol content in plant extracts | |
Total phenol and total flavonoid determination | Rutin | 153-18-4 | 10mM in DMSO | Total flavonoid standard; total flavonoid content determination and flavonoid activity control | |
Total phenol and total flavonoid determination | Rutin | 153-18-4 | ≥95% | Total flavonoid standard; total flavonoid determination by aluminum salt colorimetric method |
The antioxidant activity evaluation of plant extracts should avoid drawing conclusions from a single method. DPPH and ABTS are suitable for preliminary screening of free radical scavenging capacity, FRAP and CUPRAC are suitable for comparing reducing capacity, ORAC/HORAC can supplement dynamic radical absorbance evaluation, and cellular ROS models can further verify biological protective effects. Combining chemical assays, cellular assays, and component analysis enables a more accurate assessment of the antioxidant potential of plant extracts and the sources of their activity.
For more related articles, please see below:
[1] Clean Extracts, Smart Solvents: The Natural Extraction Reagent Playbook