Determination of Total Flavonoids Content in Sea Buckthorn: Testing Methods, Standards and Applicati

Total flavonoids are the key quality marker in sea buckthorn (Hippophae rhamnoides) berries, extracts and finished health products, and accurate determination is essential for specification setting, label claims and regulatory compliance. This article explains the applicable sample types, target analytes, spectrophotometric and HPLC-based test methods, relevant standards such as GB/T 40636-2021, and practical guidance for commissioning analysis in accredited third-party laboratories.

Technical Overview

Sea buckthorn (Hippophae rhamnoides L., family Elaeagnaceae) is a berry-bearing shrub widely cultivated in Asia and Europe. Its fruits, seeds, leaves and bark accumulate a characteristic profile of bioactive flavonoids dominated by flavonols and their glycosides, principally quercetin, kaempferol and isorhamnetin, together with rutin, hyperoside and related 3-O-glycosides. Isorhamnetin glycosides are widely regarded as the chemotaxonomic fingerprint of the species.

Because flavonoids account for a large share of the antioxidant and vascular-protective activity attributed to sea buckthorn, total flavonoid content is the principal acceptance criterion for raw materials, standardized extracts and finished health foods. Results are typically expressed as rutin equivalents (RE) or quercetin equivalents (QE) in mg/g, mg/100 g or percent by weight, or as the sum of aglycones (quercetin, kaempferol and isorhamnetin) after acid hydrolysis.

Current testing practice combines the HPLC procedure of GB/T 40636-2021 for the determination of flavonoids in sea buckthorn fruit, pharmacopoeial colorimetric assays for total flavonoids, and the method validation and quality assurance principles of GB/T 27404, executed within laboratories accredited to ISO/IEC 17025.

Testing Samples

Fresh, Frozen and Dried Berries

Whole berries are the most common submission. Fresh and frozen samples are homogenized and lyophilized or oven-dried below 60 °C, then milled to 40–60 mesh to ensure representative subsampling. Moisture is determined in parallel so that results can be reported on a dry-weight basis.

Juices, Concentrates and Purees

Liquid and semi-solid fruit products are homogenized, degreased with n-hexane where necessary, and extracted with aqueous ethanol before cleanup. High sugar and organic acid matrices require solid-phase extraction to remove interferences prior to HPLC injection.

Standardized Extracts and Powders

Commercial sea buckthorn extracts are frequently sold with guaranteed total flavonoid levels of 10% to 40% (as rutin). These high-value materials are tested for both total flavonoids and individual marker glycosides to confirm standardization and detect adulteration with exogenous rutin or quercetin.

Leaves, Teas and Botanical Cuttings

Sea buckthorn leaves often contain higher flavonoid levels than the fruit and are used in herbal teas. Dried leaf samples are milled and extracted under the same conditions as berries, with results reported on a dry basis.

Finished Health Foods and Cosmetics

Capsules, tablets, softgels, oral liquids and functional foods are prepared by de-husing, grinding and extracting the fill or matrix. Emulsion-based cosmetic formulations are broken with ethanol and the flavonoid fraction partitioned prior to analysis.

Testing Items

Typical analytical scopes for sea buckthorn flavonoid testing include the following items:

• Total flavonoids expressed as rutin or quercetin equivalents (colorimetric or hydrolysis-based calculation)
• Individual glycoside markers: rutin, hyperoside, isoquercitrin, isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucoside
• Sum of aglycones after acid hydrolysis: quercetin, kaempferol, isorhamnetin
• Aglycone ratio profiling (quercetin/kaempferol/isorhamnetin) for authenticity verification
• Supporting tests: moisture, total ash, extract solvent residues and heavy metals under the GB 5009 series where required for full specification release

Testing Methods

Colorimetric UV-Vis Spectrophotometry

The classical pharmacopoeial method uses the sodium nitrite–aluminum nitrate–sodium hydroxide system. Flavonoids chelate aluminum to form a red complex measured at 500–510 nm against a rutin calibration curve, typically linear from 0 to 200 µg/mL with R² above 0.999. An alternative aluminum trichloride assay read at 415–420 nm is preferred for flavonol-rich matrices. The method is fast, inexpensive and well suited to routine total-content screening, although ascorbic acid, phenolic acids and anthocyanins may cause positive bias in juice and berry matrices.

HPLC-UV/DAD Determination

High performance liquid chromatography, as specified in GB/T 40636-2021, is the reference approach for accurate quantification. Separation is performed on a C18 column (250 mm × 4.6 mm, 5 µm) with a gradient of acetonitrile or methanol against acidified water (0.1% formic acid or dilute phosphate buffer). A photodiode-array detector monitors flavonol glycosides at 254–266 nm and aglycones at 360 nm, with UV spectra used for identity confirmation. Quantification is by external calibration, with typical limits of quantification of 0.1–0.5 mg/L and spike recoveries of 90–108%.

Sample Preparation and Acid Hydrolysis

Ground samples are extracted with 60–80% aqueous ethanol by ultrasonic assistance or reflux, usually in two cycles of 30 minutes. When the specification defines total flavonoids as the aglycone sum, the combined extract is hydrolyzed with approximately 2 mol/L hydrochloric acid at 80 °C for one hour under nitrogen, converting all glycosides to quercetin, kaempferol and isorhamnetin prior to HPLC measurement. Polyamide or C18 solid-phase extraction cartridges remove sugars, acids and pigments from complex matrices.

UPLC and LC-MS/MS Confirmation

Ultra-performance LC shortens run times to under 15 minutes, while LC-MS/MS in multiple-reaction-monitoring mode provides unambiguous structural confirmation and low part-per-billion sensitivity. Tandem MS is recommended for dispute resolution, degradation studies and matrices with strong co-elution.

Quality Control and Method Validation

Each analytical batch includes reagent blanks, duplicate preparations, spike recovery checks and certified or in-house reference materials. Method validation covers linearity, precision (RSD below 5% for replicate preparations), trueness, LOD/LOQ and robustness in accordance with GB/T 27404. Commissioned testing should be placed with ISO/IEC 17025 accredited third-party laboratories to ensure internationally recognized traceability of results.

Applications

• Raw material qualification and supplier audits for berry processors, extract manufacturers and brand owners
• Label claim substantiation for dietary supplements, functional beverages and sea buckthorn oil capsules
• Extraction process optimization and scale-up studies comparing solvents, temperatures and hydrolysis conditions
• Stability and shelf-life studies under accelerated storage conditions per ICH-style protocols
• Conformity assessment against pharmacopoeial monographs and national food safety standards for domestic sale and export
• Scientific research on cultivar, harvest time and geographical variation of flavonoid accumulation

FAQ

What total flavonoid level is typical for sea buckthorn materials?

Reported values vary strongly with genotype, origin and part of the plant. Whole dried berries commonly contain 300–1500 mg total flavonoids per 100 g (as rutin), leaves frequently exceed 1.5% by dry weight, and commercial standardized extracts are typically guaranteed at 10–40% total flavonoids. Specifications should always state the reference compound and the calculation basis.

Which method should be chosen: colorimetry or HPLC?

Colorimetric UV-Vis screening is suitable for rapid in-process control and simple matrices, while HPLC following GB/T 40636-2021 is recommended for certification, label claims and any matrix containing vitamin C or other reducing interferents. Many laboratories run both and report HPLC as the arbitration value.

Why must the equivalence basis be specified?

Rutin, quercetin and aglycone-sum calculations produce numerically different results for the same sample because of differing molecular weights and response factors. Comparing results expressed on different bases is a frequent cause of supplier–buyer disputes, so contracts should define the basis explicitly.

Is acid hydrolysis always required?

No. Hydrolysis is required only when the specification defines total flavonoids as the sum of quercetin, kaempferol and isorhamnetin aglycones. Direct HPLC determination of intact glycosides is preferred when individual marker profiling is needed.

How much sample is needed and how long does testing take?

A representative sample of 50–200 g (or 100–250 mL for liquids) sealed in light-protected containers is generally sufficient. Standard turnaround at accredited third-party laboratories is five to ten working days, with express services available for urgent release decisions.