EPS Polysaccharide Molecular Weight Determination: Methods, Standards, and Analytical Services

Exopolysaccharide (EPS) molecular weight determination is a critical analytical service for characterizing microbial polysaccharides used in food, pharmaceutical, cosmetic, and biomedical applications. Using advanced techniques such as high-performance size exclusion chromatography (HPSEC/SEC) and multi-angle light scattering (SEC-MALS), our laboratory delivers accurate molecular weight averages, distribution profiles, and polydispersity data to support your research and product development.

Technical Overview

Exopolysaccharides (EPS) are high-molecular-weight carbohydrate polymers secreted by microorganisms, including lactic acid bacteria, fungi, yeasts, and microalgae. The molecular weight of EPS is one of its most important physicochemical parameters, directly governing its rheological behavior, water-binding capacity, emulsifying activity, and biological functions such as immunomodulation, antioxidant activity, and prebiotic effects.

Because microbial EPS typically spans a broad range from approximately 10 kDa to several million Daltons, precise molecular weight determination requires specialized chromatographic and light-scattering techniques. Our laboratory provides comprehensive EPS molecular weight characterization services, including weight-average molecular weight (Mw), number-average molecular weight (Mn), z-average molecular weight (Mz), peak molecular weight (Mp), and molecular weight distribution (MWD), enabling researchers and manufacturers to establish reliable structure-function relationships and ensure batch-to-batch consistency.

Testing Samples

Bacterial Exopolysaccharides

We analyze EPS isolated from lactic acid bacteria (Lactobacillus, Lactiplantibacillus, Lacticaseibacillus, Streptococcus thermophilus, Pediococcus, Leuconostoc), as well as industrial bacterial polysaccharides including xanthan gum, dextran, gellan gum, and curdlan produced by Xanthomonas, Leuconostoc, Sphingomonas, and Alcaligenes species.

Fungal Exopolysaccharides

Our services cover EPS from edible and medicinal fungi, including schizophyllan from Schizophyllum commune, scleroglucan from Sclerotium rolfsii, pullulan from Aureobasidium pullulans, beta-glucans from Ganoderma lucidum, Cordyceps species, and Paecilomyces, as well as polysaccharides from submerged fermentation of medicinal mushrooms.

Microalgal and Cyanobacterial EPS

We characterize extracellular polysaccharides from microalgae and cyanobacteria such as Spirulina, Chlorella, Porphyridium, Anabaena, and Nostoc, which often exhibit sulfated groups and extremely high molecular weights requiring special chromatographic configurations.

Fermentation Broth and Purified Products

Samples may be submitted as purified lyophilized EPS powder, dialyzed and freeze-dried fermentation products, or partially purified fractions. Our team can also provide pretreatment services, including deproteinization, dialysis, and freeze-drying, if required.

Testing Items

• Weight-average molecular weight (Mw)
• Number-average molecular weight (Mn)
• Z-average molecular weight (Mz)
• Peak molecular weight (Mp)
• Polydispersity index (PDI = Mw/Mn)
• Complete molecular weight distribution profile and chromatogram
• Intrinsic viscosity and Mark-Houwink parameters (optional, with online viscometry)
• Radius of gyration (Rg) and conformation analysis (optional, with MALS)
• Homogeneity and aggregation assessment

Testing Methods

High-Performance Size Exclusion Chromatography (HPSEC/SEC)

HPSEC coupled with a refractive index (RI) detector is the most widely used method for EPS molecular weight determination. The sample is dissolved in an appropriate mobile phase, typically 0.1 M sodium nitrate (NaNO3) with 0.02% sodium azide or ultrapure water, and separated on aqueous SEC columns covering a separation range of 10 to 7,000 kDa. Molecular weight is calculated against a calibration curve constructed with narrow-dispersity standards, most commonly the pullulan standard series, with dextran and polyethylene glycol standards available as alternatives.

SEC-MALS for Absolute Molecular Weight

For high-accuracy requirements, we offer size exclusion chromatography coupled with multi-angle light scattering and refractive index detection (SEC-MALS-RI). This configuration determines absolute molecular weight without relying on calibration standards, eliminating errors caused by differences in hydrodynamic volume between EPS samples and reference polymers. MALS is strongly recommended for branched, sulfated, or unusually shaped EPS where conventional calibration may produce significant deviations.

Sample Preparation Protocol

• Sample requirement: 10-20 mg of purified dry EPS powder per test
• Dissolution: samples are hydrated in mobile phase at 0.5-2 mg/mL, typically with gentle overnight stirring at room temperature or 40°C for highly viscous polysaccharides
• Filtration: solutions are filtered through 0.45 μm or 0.22 μm membranes to remove insoluble particles
• Injection volume: 50-200 μL depending on column configuration
• Column temperature: maintained at 30-45°C to improve mass recovery for high-MW samples

Supplementary Techniques

For low-molecular-weight EPS fragments or enzymatic hydrolysates, MALDI-TOF mass spectrometry can determine precise mass-to-charge ratios of individual oligosaccharide chains. Asymmetric flow field-flow fractionation (AF4) is available for ultrahigh-molecular-weight or strongly aggregating EPS that exceeds the exclusion limit of SEC columns.

Applications

• Food industry: correlating EPS molecular weight with thickening, gelling, stabilizing, and texturizing performance in yogurt, fermented beverages, and plant-based products
• Nutraceuticals and functional foods: characterizing prebiotic activity and structure-function relationships of EPS from probiotic strains
• Pharmaceutical research: supporting drug delivery carrier design, immunomodulatory activity studies, and antitumor polysaccharide development
• Cosmetics: evaluating moisturizing, film-forming, and rheological properties of EPS-based ingredients
• Biomedical engineering: assessing EPS suitability for hydrogel scaffolds and biomaterial formulations
• Quality control: verifying batch consistency, monitoring degradation during processing or storage, and supporting stability studies
• Academic research: providing reliable molecular weight data for publications, patent applications, and regulatory submissions

FAQ

How much sample is required for EPS molecular weight determination?

A minimum of 10-20 mg of purified, freeze-dried EPS powder is recommended. If your sample requires deproteinization or dialysis pretreatment, please submit 30-50 mg to ensure sufficient material after processing.

Which calibration standards are used?

Pullulan standards are the default choice for most microbial EPS because of their neutral, linear structure and wide commercial availability. Dextran and PEG/PEO standards can be substituted upon request, and SEC-MALS analysis is available when absolute molecular weight determination is preferred.

Can highly viscous or extremely high-molecular-weight EPS be tested?

Yes. For highly viscous samples, we optimize dissolution concentration, temperature, and injection volume. For EPS exceeding the SEC column range or showing aggregation, we employ large-pore columns, elevated temperature conditions, or field-flow fractionation as appropriate.

Why do calibration-based and MALS results sometimes differ?

Calibration-based SEC estimates molecular weight from hydrodynamic volume relative to standards, so branched or compact EPS molecules may be underestimated. SEC-MALS measures absolute molecular weight directly from light scattering, and is therefore considered more accurate for structurally complex EPS.

What is the typical turnaround time?

Standard HPSEC analysis is typically completed within 5-10 business days after sample receipt. SEC-MALS, supplementary viscosity measurements, or projects requiring extensive pretreatment may require additional time, which will be confirmed in the project quotation.

What deliverables are provided?

You will receive a full technical report containing the chromatogram, molecular weight distribution curve, Mw, Mn, Mp, Mz, polydispersity index, calculation method, instrumental conditions, and calibration information, suitable for research publications and regulatory documentation.