Technical articles
β-Glucan Content Determination Methods, Sample Pretreatment and Quality Control
β-Glucan Content Determination Methods, Sample Pretreatment and Quality Control
β-Glucan is a class of polysaccharides formed by glucose residues linked through β-glycosidic bonds. It is widely present in oats, barley, yeast, fungi, algae and some microbial-derived materials. β-Glucans from different sources vary greatly in linkage type, branching degree, molecular weight and solubility. Therefore, content determination should not focus only on “total sugar content”; method selection should also consider sample matrix, structural characteristics and method applicability.
Keywords: β-glucan; content determination; enzymatic assay; polysaccharide analysis; sample pretreatment; quality control; fungal polysaccharides
1 Objects and Analytical Challenges in β-Glucan Determination
1.1 Structural Differences of β-Glucan
(1) Cereal-derived β-glucan
β-Glucans in oats and barley are mainly β-(1→3)(1→4)-D-glucans, usually with good water solubility and viscosity characteristics. These samples are commonly found in cereals, dietary fiber ingredients, beverages, compressed candies, solid beverages and functional foods. Enzymatic methods are commonly used for content determination.
(2) Yeast- and fungal-derived β-glucan
β-Glucans in yeast cell walls and fungal polysaccharides mostly contain a β-(1→3) main chain and β-(1→6) branches, and often coexist with proteins, mannans, chitin or cell wall residues. Pretreatment of such samples is more complex and often requires alkaline extraction, acid hydrolysis, enzymatic digestion or specific polysaccharide release steps.
(3) β-Glucan in complex formulations
In foods, health products, fermented products and plant extracts, β-glucan may coexist with starch, dextrin, pectin, arabinoxylan, mannan, protein and pigments. If pretreatment is insufficient, total sugar methods may overestimate the result, while enzymatic methods may show low recovery.
1.2 Core Issues in Content Determination
(1) Specificity
β-Glucan determination should distinguish the target β-glycosidic bond structure from other glucans or heteropolysaccharides as much as possible. Total sugar methods only reflect total carbohydrate levels and cannot directly represent β-glucan content. Enzymatic methods and structural analysis methods are more suitable for specific evaluation.
(2) Solubility
The solubility of β-glucan is affected by source, molecular weight, extraction process, particle structure and heat treatment. If the sample is not fully dispersed or dissolved, the result will be underestimated. If excessive hydrolysis or strong acid treatment is used, the target structure may be altered.
(3) Matrix interference
Starch, free glucose, reducing sugars, proteins, pigments, polyphenols and salts may all affect test results. Complex samples require blanks, spike recovery and necessary interference-removal steps.
2 Common Determination Methods
2.1 Enzymatic Assay
(1) Basic principle
Enzymatic assays usually use specific endo-enzymes or exo-enzymes to hydrolyze β-glucan into oligosaccharides or glucose, followed by quantification using a glucose oxidase-peroxidase chromogenic system, hexokinase system or another glucose detection system. This method has good specificity and is suitable for cereal β-glucan and some properly treated fungal β-glucan samples.
(2) Determination of cereal β-glucan
β-(1→3)(1→4)-glucan in oats, barley and their processed products is usually hydrolyzed by lichenase or β-1,3-1,4-glucanase, and then further converted into glucose by β-glucosidase. The β-glucan content is then calculated according to the generated glucose amount.
(3) Determination of fungal or yeast β-glucan
Yeast- and fungal-derived samples often require removal of free sugars, α-glucan or soluble interfering components before β-glucan-derived glucose is released through acid hydrolysis or specific enzymatic digestion. For cell wall-type samples, the adequacy of pretreatment directly determines result reliability.
2.2 Phenol-Sulfuric Acid Method
(1) Method characteristics
The phenol-sulfuric acid method can determine total sugar content in samples. It is relatively simple and has high sensitivity. Its principle is that polysaccharides are dehydrated by concentrated sulfuric acid to form furfural derivatives, which then react with phenol to produce colored products for absorbance-based quantification.
(2) Applicable scope
This method is suitable for evaluating total sugar content in polysaccharide extracts, monitoring process changes and roughly comparing polysaccharide levels among different sample batches. For highly purified β-glucan samples with limited interference from other sugars, it can serve as an auxiliary quantitative method.
(3) Limitations
The phenol-sulfuric acid method does not have β-glucan structural specificity. Starch, dextrin, sucrose, pectin, hemicellulose and other hydrolyzable sugars may all contribute to the signal. Therefore, it cannot be directly used for specific quantification of β-glucan in complex samples.
2.3 Congo Red Method
(1) Method characteristics
Congo red can form complexes with some β-glucans and cause changes in the absorption spectrum. This method can be used to evaluate the triple-helix conformation, relative content or structural state of β-glucan.
(2) Applicable scenarios
The Congo red method is often used in fungal polysaccharide, yeast β-glucan and polysaccharide conformation studies. It is suitable for comparing the effects of different extraction processes on polysaccharide conformation and binding capacity.
(3) Limitations
Congo red binding is strongly affected by molecular weight, conformation, pH, salt concentration and impurities. It is usually not suitable as the only absolute quantitative method. For quality evaluation, it should be used together with enzymatic assays, total sugar methods or chromatographic analysis.
2.4 Chromatographic and Structural Analysis Methods
(1) HPLC or ion chromatography
After acid hydrolysis or enzymatic hydrolysis, β-glucan can be analyzed by HPLC or ion chromatography to detect glucose and related oligosaccharides. This method is suitable for sugar composition analysis and hydrolysis product quantification.
(2) Gel permeation chromatography
Gel permeation chromatography can be used to analyze the molecular weight distribution of β-glucan. Molecular weight is an important factor affecting viscosity, biological activity, solubility and processing properties, so it is often used together with content determination.
(3) NMR and mass spectrometry
Nuclear magnetic resonance, mass spectrometry and methylation analysis can be used to confirm glycosidic linkage type, branching structure and monosaccharide composition. These methods are more suitable for structural identification and high-level quality research, and are not necessarily routine batch testing methods.
3 Sample Pretreatment Strategies
3.1 Cereal and Food Samples
(1) Grinding and homogenization
Cereal samples should be fully ground and homogenized to avoid sampling bias caused by particle size differences. Samples containing bran, flaked cereals or composite cereal powders especially require control of particle size and sampling representativeness.
(2) Starch removal
Cereal samples contain high levels of starch. If total sugar methods or non-specific hydrolysis methods are used directly, β-glucan content may be significantly overestimated. In enzymatic assays, α-amylase, amyloglucosidase and related steps are usually required to reduce starch interference.
(3) Fat and protein interference
In high-fat cereal products or complex formulations, fat may affect sample dispersion, while protein may affect enzymatic hydrolysis efficiency and chromogenic background. Defatting, protein precipitation or sample blank subtraction may be required when necessary.
3.2 Yeast and Fungal Samples
(1) Cell wall disruption
Yeast and fungal β-glucans are often located in the cell wall, and simple water extraction may result in insufficient release. Mechanical disruption, alkaline treatment, hot-water extraction or enzymatic digestion can improve β-glucan release efficiency.
(2) α-Glucan removal
Some fungal samples contain α-glucan, glycogen or starch-like polysaccharides. If the detection system cannot distinguish α-glucan from β-glucan, specific enzymatic digestion or selective pretreatment is required to remove α-glucan interference.
(3) Protein and pigment treatment
Fungal extracts often contain proteins, polyphenols and pigments. Proteins may affect enzymatic digestion and turbidity, while pigments may interfere with absorbance detection. Centrifugation, precipitation, dialysis or solid-phase cleanup should be used to reduce background when needed.
3.3 Fermentation Broth and Liquid Samples
(1) Centrifugal clarification
Fermentation broth contains cells, extracellular polysaccharides, proteins and culture medium residues. Before testing, it is necessary to distinguish “extracellular β-glucan” from “cell wall β-glucan” according to the target analyte and design separate pretreatment workflows.
(2) Free sugar subtraction
Fermentation broth and beverage samples may contain glucose, maltose, sucrose or other reducing sugars. If β-glucan is calculated based on generated glucose, free sugar background should be subtracted.
(3) Concentration and desalting
Low-content samples can be concentrated to improve detection sensitivity. High-salt samples may affect enzyme activity or chromatographic separation, so dialysis, ultrafiltration or desalting columns may be required.
4 Method Selection and Result Conversion
4.1 Principles of Method Adaptation
(1) Enzymatic methods are preferred for cereal samples
The structure of β-glucan in oats, barley and their products is relatively clear. Enzymatic methods have good specificity and repeatability and are suitable as the main quantitative method.
(2) Structural validation is required for fungal samples
Samples such as yeast, Ganoderma, shiitake and Schizophyllum have highly variable β-glucan structures. If only total sugar methods are used, interference from other polysaccharides is likely. If only enzymatic methods are used, insufficient extraction may lead to underestimation. A combined evaluation using enzymatic assays, total sugar methods, enzymatic digestion validation or structural analysis is recommended.
(3) Recovery testing is required for complex formulations
Complex foods, health products and plant extracts have complicated matrices. Spike recovery, parallel samples and blank subtraction must be performed. Otherwise, even if the method itself is reliable, matrix effects may lead to biased results.
4.2 Result Expression
(1) Mass fraction
Solid samples are usually expressed as g/100 g, mg/g or %. The result should specify whether it is on a dry basis or wet basis to avoid batch comparison bias caused by moisture differences.
(2) Liquid concentration
Liquid samples can be expressed as mg/mL, μg/mL or mg/L. For fermentation broth samples, it should be clearly stated whether the detected material is supernatant, precipitate, the total fermentation system or the extracted polysaccharide fraction.
(3) Conversion factor
Enzymatic methods often calculate β-glucan content according to the amount of generated glucose. Because glucose polymerization into polysaccharides involves dehydration condensation, a corresponding conversion relationship is usually required between glucose and glucan. Actual calculations should follow the method instructions and standard setup consistently.
4.3 Standard Curve and Quality Control
(1) Standard selection
If a glucose chromogenic method is used, glucose standards should be used to establish the standard curve. If a direct β-glucan detection system is used, β-glucan standards with a source and structure as close as possible to the sample should be selected.
(2) Linear range
The concentration range of the standard curve should cover the detection concentration of the sample. If sample absorbance exceeds the linear range, the sample should be diluted and retested rather than calculated by extrapolation.
(3) Spike recovery
Spike recovery can evaluate pretreatment and matrix interference. For complex samples, dark-colored samples and high-protein samples, spike recovery better reflects method accuracy than parallel repeatability alone.
5 Common Interfering Factors
5.1 Starch and α-Glucan Interference
(1) Interference from starch hydrolysis
After acid hydrolysis or non-specific enzymatic hydrolysis, starch can produce glucose, leading to overestimation of β-glucan results. Starch removal or α-glucan subtraction is especially important for cereal samples.
(2) Glycogen interference
Yeast and animal-derived samples may contain glycogen. Glycogen is an α-glucan and may interfere with total glucose-based methods if not removed.
(3) Influence of method selection
Enzymatic methods have higher specificity than total sugar methods, but different enzyme systems have different structural compatibility. Appropriate enzyme combinations should be selected according to the source of β-glucan.
5.2 Free Sugar and Oligosaccharide Interference
(1) Free glucose
Free glucose in samples directly enters the glucose detection system and causes overestimation. A sample blank should be included before determination, or free sugars should be removed by washing or dialysis.
(2) Maltodextrin and oligosaccharides
Compound foods often contain maltodextrin, oligosaccharides or soluble dietary fibers. These components may contribute signals in acid hydrolysis or total sugar methods.
(3) Sugar alcohols and sweeteners
Some sweeteners have limited interference with chromogenic systems, but high concentrations of sugar alcohols may affect system viscosity, enzymatic reaction or sample dilution accuracy.
5.3 Pigment, Protein and Polyphenol Interference
(1) Pigment background
Dark extracts, fermented samples or plant concentrates may have absorption background at specific wavelengths. A sample background blank should be included, and decolorization or dilution should be performed where possible.
(2) Protein effects
Proteins may cause turbidity, precipitation or enzyme reaction inhibition. High-protein samples can be treated by protein precipitation, centrifugal clarification or appropriate dilution to reduce interference.
(3) Polyphenol effects
Polyphenols can interact with polysaccharides, proteins or chromogenic reagents and affect absorbance results. Polyphenol interference is especially important in plant samples.
6 Quality Control and Result Evaluation
6.1 Accuracy Control
(1) Standard calibration
Standards should be freshly prepared or stored according to stability requirements. For glucose standard curves, contamination and concentration deviation should be avoided. For β-glucan standards, complete dissolution, source differences and batch consistency should be considered.
(2) Spike recovery control
The spike level should be close to the actual sample content. Low recovery may indicate insufficient extraction, incomplete enzymatic hydrolysis or matrix inhibition. High recovery may indicate insufficient background subtraction or non-specific hydrolysis.
(3) Method comparison
For important samples, enzymatic methods can be cross-validated with total sugar methods, chromatographic methods or structural analysis methods. If the results differ greatly, sample pretreatment and method specificity should be checked first.
6.2 Precision Control
(1) Parallel samples
Each sample should be measured at least in parallel. For complex samples, full-process parallel testing from weighing and extraction to detection is recommended, rather than parallel testing only at the chromogenic step.
(2) Within-batch repeatability
For the same batch of samples, enzymatic hydrolysis time, temperature, pH, color development time and reading wavelength should be recorded to avoid result fluctuations caused by operational differences.
(3) Between-batch consistency
For long-term quality control, quality control samples or internal reference samples should be included. Method confirmation is required after changing reagent, enzyme or standard batches.
6.3 Reporting Points
(1) State the sample form
The report should specify whether the sample is a raw material, extract, fermentation broth, solid preparation or compound food, and should describe the pretreatment method before determination.
(2) State the method type
The report should clearly state whether an enzymatic method, total sugar method, Congo red method, chromatographic method or another method was used. The “β-glucan content” obtained by different methods may not be directly comparable.
(3) State the calculation basis
For solid samples, dry basis or wet basis should be specified. For liquid samples, dilution factor, extraction volume and result unit should be stated. If a conversion factor is used, it should be kept consistent across batches.
7 Reagents and System Construction for β-Glucan Content Determination
7.1 β-Glucan Standards, Enzyme Systems and Quality Control Tools
Product Module | Cat. No. | Product Name | CAS No. | Grade/Purity | System Role | Applicable Research Direction |
Standard substrate | β-1,3-Glucan | 9051-97-2 | ≥70% | Method establishment and structural specificity control | Suitable for β-(1→3)-glucan enzymatic specificity evaluation and structural analysis control | |
Standard substrate | β-D-Glucan from barley | 9041-22-9 | ≥80% | Cereal β-glucan standard substrate | Suitable for method establishment and recovery evaluation of cereal β-(1→3)/(1→4)-glucan | |
Standard substrate | β-D-Glucan from barley | 9041-22-9 | ≥95% | High-purity cereal β-glucan standard substrate | Suitable for standardized analysis of high-purity cereal β-glucan | |
Standard substrate | β-Glucan | 9012-72-0 | Derived from brewing yeast, with a content of ≥70% | Yeast-derived β-glucan standard substrate | Suitable for total determination of yeast β-glucan and optimization of pretreatment conditions | |
Standard substrate | β-Glucan | 9012-72-0 | Derived from brewing yeast, with a content of ≥80% | Yeast-derived β-glucan standard substrate | Suitable for quantification of yeast-derived β-glucan and evaluation of enzymatic digestion systems | |
Standard substrate | β-Glucan | 9012-72-0 | ≥90% | High-content β-glucan standard material | Suitable for standardized analysis of high-content β-glucan | |
Target enzyme | Beta-glucanase | EnzymoPure™, ≥100 FBG/g | Selectively hydrolyzes cereal mixed-linkage β-glucan | Suitable for selective enzymatic digestion of cereal β-(1→3)/(1→4)-glucan | ||
Target enzyme | β-(1→3)-D-Glucanase | 9044-93-3 | Bioactive,ActiBioPure™,Native,High Performance,EnzymoPure™,from Helix pomatia; ≥0.2 U/mg enzyme powder | Cleaves β-(1→3)-glucan main chains | Suitable for cleavage analysis of yeast/fungal β-(1→3)-glucan main chains | |
Target enzyme | β-1,3-1,4-Glucanase | 62213-14-3 | Hydrolyzes β-(1→3)(1→4)-mixed-linkage glucan | Suitable for structural analysis of cereal mixed-linkage β-glucan | ||
Target enzyme | Lichenase | 37288-51-0 | Bioactive,Recombinant,ActiBioPure™,High Performance,EnzymoPure™,≥1000 U/ml | Specifically hydrolyzes cereal β-glucan and releases oligosaccharides | Suitable for oligosaccharide release from cereal β-glucan and DP3/DP4 profiling | |
Target enzyme | β-Glucanase from Trichoderma sp. | 9074-98-0 | technical grade, ≥50 U/mg powder | Crude enzymatic digestion of β-glucan | Suitable for crude β-glucan enzymatic digestion and process screening | |
Target enzyme | β-Glucanase from Aspergillus niger | powder, dark brown, ~1 U/mg | Preliminary enzymatic digestion of β-glucan | Suitable for preliminary construction of β-glucan enzymatic digestion systems | ||
Endpoint conversion enzyme | β-Glucosidase | 9001-22-3 | Bioactive, ActiBioPure™, Native, High Performance, EnzymoPure™, ≥10U/mg powder; 10-60 U/mg protein | Further converts oligosaccharides into glucose | Suitable for endpoint conversion of oligosaccharides to glucose | |
Endpoint conversion enzyme | β-Glucosidase | 9001-22-3 | Bioactive, ActiBioPure™, Native, High Performance, EnzymoPure™, ≥4 U/mg powder | Generates endpoint glucose | Suitable for endpoint glucose generation assays | |
Interference-removal enzyme | Amylase | 9000-90-2 | EnzymoPure™, 480 KNU-B/g | Degrades starch interference | Suitable for starch removal in cereal sample pretreatment | |
Interference-removal enzyme | α-Amylase | 9000-90-2 | EnzymoPure™, BioReagent | Routine starch removal | Suitable for routine starch removal treatment | |
Interference-removal enzyme | α-Amylase from Bacillus subtilis | 9000-90-2 | EnzymoPure™, Native, ≥50 U/mg powder | Degrades starch in samples | Suitable for starch removal in sample pretreatment | |
Interference-removal enzyme | α-Amylase | 9000-90-2 | Bioactive,ActiBioPure™,High Performance,EnzymoPure™,≥135 KNU/g; from Bacillus licheniformis | Removes starch under hot extraction conditions | Suitable for starch degradation under hot extraction conditions | |
Interference-removal enzyme | Amyloglucosidase from Aspergillus niger | 9032-08-0 | lyophilized powder, 30-60 units/mg protein (biuret), ≤0.02% glucose | Hydrolyzes residual starch and dextrin | Suitable for removing residual starch and dextrin interference | |
Interference-removal enzyme | Amyloglucosidase from Aspergillus niger | 9032-08-0 | Native, EnzymoPure™, ≥100 U/mg powder | Thoroughly hydrolyzes residual starch | Suitable for thorough hydrolysis of residual starch in cereal samples | |
Interference-removal enzyme | Amyloglucosidase from Aspergillus niger | 9032-08-0 | Bioactive, ActiBioPure™, High Performance, EnzymoPure™, ≥20mg/mL protein | High-activity starch removal | Suitable for high-activity starch-removal pretreatment | |
Interference-removal enzyme | Amyloglucosidase from Aspergillus niger | 9032-08-0 | EnzymoPure™, liquifying，100000u/ml | Efficiently hydrolyzes starch-type interferents | Suitable for pretreatment of high-starch background samples | |
Interference-removal enzyme | Proteinase K | 39450-01-6 | EnzymoPure™, lyophilized powder，≥30 units/mg protein | Removes proteinaceous matrix and exposes cell wall polysaccharides | Suitable for proteinaceous matrix removal and cell wall exposure | |
Interference-removal enzyme | Proteinase K | 39450-01-6 | EnzymoPure™, BioReagent | Protein removal | Suitable for pretreatment protein removal in yeast/fungal samples | |
Interference-removal enzyme | Proteinase K from Tritirachium album limber | 39450-01-6 | EnzymoPure™, ≥20 units/mg dry weight | Removes cell wall-associated proteins | Suitable for protein removal from cell wall-associated samples | |
Interference-removal enzyme | Proteinase K Solution (20 mg/mL) | 39450-01-6 | BioReagent,DNase, RNase free,Suitable for molecular biology,sterile,≥95%(Native-PAGE),20 mg/mL | Ready-to-use protein removal | Suitable for ready-to-use pretreatment systems | |
Endpoint detection enzyme | Glucose Oxidase (GOD) | 9001-37-0 | EnzymoPure™, Native, ≥10000 GODU/g solid;from Aspergillus oryzae | Endpoint glucose oxidation detection | Suitable for glucose oxidase endpoint detection systems | |
Endpoint detection enzyme | Glucose Oxidase from Aspergillus niger | 9001-37-0 | EnzymoPure™,Native,≥100 U/mg enzyme powder | Endpoint reaction for glucose quantification | Suitable for glucose quantitative endpoint enzyme systems | |
Endpoint detection enzyme | Glucose Oxidase from Aspergillus niger | 9001-37-0 | Bioactive,ActiBioPure™,High Performance,EnzymoPure™,Lyophilized powder,≥180 U/mg enzyme powder | High-sensitivity glucose endpoint detection | Suitable for validating high-sensitivity glucose endpoint detection systems | |
System validation | β-1,3-Glucanase (β-1,3-GA) Activity Assay Kit (Micro Method) | BioReagent | Validates β-(1→3)-glucanase activity | Suitable for β-(1→3)-glucanase activity validation | ||
System validation | β-1,3-Glucanase (β-1,3-GA) Activity Assay Kit (Colorimetric Method) | BioReagent | Validates β-(1→3)-glucanase activity | Suitable for β-(1→3)-glucanase activity validation | ||
System validation | β-Glucosidase (β-GC) Activity Assay Kit (Micro Method) | BioReagent | Evaluates endpoint conversion enzyme activity | Suitable for endpoint conversion enzyme activity evaluation | ||
System validation | β-Glucosidase (β-GC) Activity Assay Kit (Colorimetric Method) | BioReagent | Evaluates endpoint conversion enzyme activity | Suitable for endpoint conversion enzyme activity evaluation | ||
System validation | Glucose Oxidase (GOD) Activity Assay Kit (Micro Method) | BioReagent | Validates glucose endpoint detection system | Suitable for glucose endpoint detection system validation | ||
System validation | Glucose Oxidase (GOD) Activity Assay Kit (Colorimetric Method) | BioReagent | Validates glucose endpoint detection system | Suitable for glucose endpoint detection system validation |
7.2 Method Matching for Different Sample Types
Sample Type | Recommended Main Method | Auxiliary Method | Pretreatment Focus | Key Points in Result Evaluation |
Oat and barley raw materials | Enzymatic assay | Total sugar method, molecular weight analysis | Grinding, homogenization, starch removal | β-(1→3)(1→4)-glucan content and batch stability |
Cereal solid beverages | Enzymatic assay | Spike recovery, blank subtraction | Removal of free sugar and dextrin interference | Pay attention to the influence of starch hydrolysates in the formulation |
Yeast β-glucan | Enzymatic assay combined with pretreatment | Total sugar method, enzymatic digestion validation | Cell wall disruption, α-glucan removal | Focus on release efficiency and α/β structure distinction |
Fungal polysaccharide extracts | Enzymatic assay or total sugar method combined with structural validation | Congo red method, HPLC, GPC | Deproteinization, decolorization, small-molecule sugar removal | Distinguish β-glucan from other heteropolysaccharides |
Fermentation broth | Enzymatic assay or total sugar method | Dialysis, chromatographic analysis | Distinguish extracellular polysaccharides from cellular polysaccharides | Culture medium and free sugar background should be subtracted |
Health food complex formulations | Enzymatic assay plus recovery validation | Total sugar method, HPLC | Removal of pigments, proteins and free sugars | Focus on matrix interference and method recovery |
The reliability of β-glucan content determination depends on method specificity, sample pretreatment and the logic of result conversion. Cereal samples should preferably be analyzed by enzymatic methods. Fungal and yeast samples require attention to cell wall release and structural validation. Complex formulations should use blank subtraction and spike recovery to control matrix interference. Only by matching sample source, β-glucan structure and detection method can results with comparability and interpretive value be obtained.