Size Exclusion Chromatography/multi-angle Laser Light Scattering Research Articles

Effect of sheeting stress and heating on the molecular chain structure, size, and conformation of gluten proteins during noodle processing

In this paper, the changes in molecular structure, size distribution, and conformation of gluten induced by the mechanical stress during sheeting and the heating effect during cooking of noodles were investigated by atomic force microscopy (AFM), X-ray scattering (SAXS), and size-exclusion chromatography multi-angle laser light scattering (SEC-MALLS). AFM results showed that the height and width of gluten molecular chains were decreased after calendering and increased post-cooking. Calendering reduced the molecular size and compacted the gluten network (increased Dm). The SDS extractable gluten components showed a quasi-spherical chain conformation but gradually changed to a random coil conformation due to heating. According to SEC-MALLS profiles, calendering and appropriate heating (4 min) promoted the homogeneity of molecular mass of glutenin polymer. The mechanical depolymerization and the heat-promoted polymerization of gluten could be due to the breakage and formation of disulfide bonds and the interconversion of sulfhydryl groups.

Synthesis of Novel pH-Tunable Thermoresponsive Hydroxyl-Terminated Hyperbranched Polyether.

In this study, a new pH-tunable thermoresponsive hydroxyl-terminated hyperbranched polyether (HTHP 2) was successfully prepared via a one-pot cationic polymerization technique and postmodification. In the first step, hydroxyl-terminated hyperbranched polyether containing double bonds (HTHP 1) were synthesized. Then, through thiol-ene “click” reaction, pH-responsive carboxyl groups were introduced to the target polymer of HTHP 2. The products were characterized via Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), and size-exclusion chromatography-multiangle laser light scattering (SEC-MALLS). Moreover, dynamic light scattering (DLS) and UV–Vis spectroscopy was employed to study the pH- and thermoresponsiveness in detail. Results showed that HTHP 2 possessed typical pH-controllable thermoresponsive behavior. By regulating the solution pH value range 3.0–5.4, LCST of HTHP 2 could be changed from 12.8 to 68.0 °C. Meanwhile, the cell viabilities of A549 cells were more than 80% for in vitro cytotoxicity tests of HTHP 2, suggested that HTHP 2 polymers are of good biocompatibility for up to 24 h.

Synthesis and Properties of Side-Chain Functionalized Polytetrahydrofuran Derivatives via the Blue-Light Photocatalytic Thiol-Ene Reaction.

A series of side-chain functionalized polytetrahydrofuran (PTHF) derivatives were synthesized via the blue-light photocatalytic thiol-ene “click” reaction. Firstly, unsaturated polytetrahydrofuran (UPTHF) as a new unsaturated polyether was synthesized via condensation polymerization of cis-2-butene-1,4-diol and trans-1,4-dibromo-2-butene using potassium hydroxide (KOH) as a catalyst. Then, double bonds in the backbone of UPTHF were modified into different pendant functionality side groups by blue-light photocatalytic thiol-ene “click” reaction using Ru(bpy)3Cl2 as a photoredox catalyst, obtaining different side-chain functionalized PTHF derivatives. The structure and the morphology of the side-chain functionalized PTHF derivatives was characterized via Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS), and differential scanning calorimeter (DSC). The results showed that the blue-light photocatalytic thiol-ene reaction exhibited high efficiency, and all the unsaturated bonds were modified. Different branch units bestowed different performance of PTHF derivatives; we systematically investigated the thermal properties, pH-triggered and temperature-triggered, self-assembly behaviors of different PTHF derivatives.

Molar Mass Analysis of Hydrophobically Modified Hyaluronic Acid by SEC‐MALLS: Facing the Challenges of Amphiphilic Biomacromolecules

AbstractA size exclusion chromatography–multiangle laser light scattering (SEC‐MALLS) method is developed for determining the molar masses of amphiphilic hyaluronan (HA), consisting of a hydrophilic polymer backbone modified to varying extents with hydrophobic, polymerizable acrylate groups. The polymers are prepared via the base‐catalyzed esterification of HA with acrylic anhydride. Various parameters are investigated including mobile phase composition, temperature, pH, salt type, and concentration in order to find the most suitable conditions for completely dissolving the modified polymers irrespective of the degree of substitution (DS), and for suppressing secondary polymer interactions. The hydrolytic and the thermal stability of the different materials at various experimental conditions are also extensively investigated. HAs with DS varying from 0 to 3.4 are subsequently analyzed at the optimized experimental conditions for the mobile phase being DMSO/H2O 60/40(v/v) with 0.05 M LiBr and an operating temperature of 40 °C. The refractive index increments (dn/dc) of the HAs are determined and the results show a dependence of dn/dc on DS.

Alkaline dissolution of native potato starch − impact of the preparation conditions on the solution properties determined by means of SEC-MALS

The preparation of molecularly dispersed solutions of starch for the characterization by means of size exclusion chromatography–multi angle laser light scattering (SEC-MALS) was investigated. Solutions were prepared by pasting granular native potato starch using strong alkali at 25°C, neutralization and subsequent dilution in DMSO with the objective of ideally complete dissolution and simultaneously absence of molecular degradation. Process parameters such as type of alkali (KOH and NaOH), starch concentration in the alkaline dispersion (1.25 and 2.50%), dissolution time (0.5, 2, and 24 h), high shear treatment of the neutralized paste (Ultra-Turrax at 0.625 and 1.25%; speed: 11 000 and 24 000 min−1; duration: 2 and 4 min) and applying an aftertreatment following dilution to final concentration (0.125 and 0.250%; stirring) were systematically varied and impacts on SEC recovery rate and Mw of the starch examined using two experimental designs. Besides high reproducibility of the molecular data obtained, the laboratory-scale preparation method provided basically very good solutions. Most factors were significant and detailed conditions ensure that a high degree of a dissolved amount and simultaneous minimal molecular degradation were identified. Solutions containing 0.250% starch with applied aftertreatment gave best results (Mw between 40 × 106 g/mol (KOH) and 35 × 106 g/mol (NaOH); corresponding SEC recovery rates of 85% or higher). A pasting duration of 2 h was found to be sufficient for nearly complete dissolution. Including a high shear treatment, the preparation process was characterized by a compromise on the achieved solution state and accompanied molecular degradation. The investigated procedure represents a suitable alternative to current existing methods.

Chemical characterization and antioxidant activity of polysaccharide extract from spent mushroom substrate of Pleurotus eryngii

Pleurotus eryngii has been widely cultivated in China and massive spent mushroom substrate (SMS) has been discarded. To utilize spent substrate of P. eryngii effectively, SMS was extracted by hot alkali liquor and a high yield (12.18%) of crude polysaccharide (designated as CPS) was obtained, then a polysaccharide-protein complex (RPS) was purified from CPS. Molecular characterization detected by size exclusion chromatography/multi-angle laser light scattering (SEC-MALLS) showed that the weight average molar mass (Mw) of RPS was 8.372×106g/mol. The molecular conformation of RPS was revealed to be a rigid rod form in aqueous solution. Monosaccharide composition analysis by GC–MS confirmed that RPS is a novel acid heteropolysaccharide and mainly composed of xylose, glucose, and arabinose. Then, FT-IR spectral analysis of RPS revealed prominent characteristic polysaccharide and protein groups. Pharmacological experiments in vitro suggested that both CPS and RPS exhibited strong antioxidant activities in a dose dependent manner, using different in vitro models like ABTS, superoxide, hydroxyl and DPPH. The high-yield crude polysaccharide showed potential for application as strong antioxidant in food industry. The study provided a reliable approach for spent resource recovery, which would be significant to sustainable development of mushroom industry and environmental protection.

Separation and molecular characterization of the amylose‐ and amylopectin‐fraction from native and partially hydrolyzed potato starch

The polysaccharide fractions amylose (AM) and amylopectin (AP) were obtained from both a native and an acid‐thinned potato starch sample. The starches were dissolved using an autoclaving and an alkaline dissolution process and fractionated by complexing the AM with 1‐butanol. The fractions were comprehensively characterized by means of size exclusion chromatography‐multi angle laser light scattering (SEC‐MALS) and iodine binding experiments. The fractions’ high purity was generally proved. Molecular degradation of both starch fractions due to autoclaving was evident and more pronounced for the acid modified sample by trend. The SEC‐chromatograms confirmed the elution of the linear AM‐fractions entirely accompanied by branched AP. Complete enzymatic debranching the starch sample prior to chromatography and mathematical peak separation was an alternative method for the molecular characterization of the AM‐fraction. However, this procedure is restricted to the non‐branched AM and found particularly suitable for partial molecular degraded starch (acid‐thinned).

What is the Contribution of Counter‐Ions to the Absolute Molar Mass of Polyelectrolytes Determined by SEC‐MALLS?

In this work, the absolute molar mass of well‐defined cationic polyelectrolytes has been determined by size‐exclusion chromatography multiangle laser light scattering (SEC‐MALLS) using different eluents containing different counter‐ions (chloride, bromide or trifluoroacetate). Narrowly polydisperse poly‐l‐lysines of different degrees of polymerization (from 20 up to ≈400) having a counter‐ion similar to the eluent are analyzed as model compounds. By comparing the average degree of polymerization obtained by SEC‐MALLS with those derived independently from NMR/viscosity experiments, it has been possible to investigate what is the average molar mass of the charged monomer that is measured in SEC‐MALLS experiments. The main result of this study is that the average molar mass of the charged monomer in a SEC‐MALLS experiment only takes into account the fraction of condensed counter‐ion associated to the monomer. This fundamental study is important in practice because the calculation of the degree of polymerization (instead of the molar mass) is often required for subsequent chemical reactions, for instance in the case of polymer functionalization. image

Preparation of Low Molecular Weight Chondroitin Sulfates, Screening of a High Anti-Complement Capacity of Low Molecular Weight Chondroitin Sulfate and Its Biological Activity Studies in Attenuating Osteoarthritis.

Chondroitin sulfate (CS) plays important roles in the complement system. However, the CS structure is complicated due to different sources and the number and positions of sulfate groups. The objective of this study was to prepare different low molecular weight chondroitin sulfates (LMWCSs) and to investigate the biological activity in anti-complement capacity. A series of LMWCSs was prepared from different sources and characterized by ultraviolet-visible (UV) spectroscopy, high-performance liquid chromatography (HPLC), size exclusion chromatography-multiangle laser light scattering (SEC-MALLS) and nuclear magnetic resonance (NMR) spectroscopy. Hemolytic, anti-complement 3 deposition capacity and cell viability assays were carried out to investigate the biological activities in vitro. The results showed that LMWCS prepared from shark cartilage with the oxidative degradation method (LMWCS-S-O) had the best anti-complement capacity. LMWCS-S-O could inhibit the alternative pathway of the complement system and protect chondrocytes from cell death. The attenuating effect of LMWCS-S-O on Osteoarthritis (OA) was investigated by destabilization of the medial meniscus (DMM) model in vivo. Functional wind-up, histological and C5b-9 analyses were used to evaluate the treatment effect on the OA model. In vivo results showed that LMWCS-S-O could attenuate OA. LMWCS-S-O with a high content of ΔDi-2,6diS and ΔDi-6S could be used for attenuating OA through regulating the complement system.

Binding of RNA by the Nucleoproteins of Influenza Viruses A and B.

This paper describes a biochemical study for making complexes between the nucleoprotein of influenza viruses A and B (A/NP and B/NP) and small RNAs (polyUC RNAs from 5 to 24 nucleotides (nt)), starting from monomeric proteins. We used negative stain electron microscopy, size exclusion chromatography-multi-angle laser light scattering (SEC-MALLS) analysis, and fluorescence anisotropy measurements to show how the NP-RNA complexes evolve. Both proteins make small oligomers with 24-nt RNAs, trimers for A/NP, and dimers, tetramers, and larger complexes for B/NP. With shorter RNAs, the affinities of NP are all in the same range at 50 mM NaCl, showing that the RNAs bind on the same site. The affinity of B/NP for a 24-nt RNA does not change with salt. However, the affinity of A/NP for a 24-nt RNA is lower at 150 and 300 mM NaCl, suggesting that the RNA binds to another site, either on the same protomer or on a neighbour protomer. For our fluorescence anisotropy experiments, we used 6-fluorescein amidite (FAM)-labelled RNAs. By using a (UC)6-FAM3′ RNA with 150 mM NaCl, we observed an interesting phenomenon that gives macromolecular complexes similar to the ribonucleoprotein particles purified from the viruses.

Effects of cigarette smoke condensate on the production and characterization of exopolysaccharides by Streptococcus mutans / Sigara dumanı kondensatının Streptococcus mutans tarafından üretilen eksopolisakkaritlerin üretimi ve karakterizasyonu üzerine etkisi

Abstract Objective: Streptococcus mutans is regarded as the major agent causing dental caries. It has been well documented that cigarette smoke affects the growth of S. mutans. This study investigate the effect of cigarette smoke condensate (CSC) on the production and characterization of exopolysaccharides (EPS) produced by S. mutans ATCC 35668. Methods: Cigarettes of Shanhua brand were used to prepare the CSC. S. mutans was cultured in MSB media with the addition of CSC under anaerobic condition. Furthermore, the EPS fraction was isolated and purified by gel filtration chro-matography on Sepharose CL-6B. The molecular characterization of EPS was analyzed by GC-MS, FT-IR and size exclusion chromatography/multiangle laser light scattering (SEC/MALLS) system. Results: The results showed that CSC at tested concentrations could significantly increase the growth of S. mutans and acetic acid production, compared with the control. The CSC was not found to affect carbohydrate composition of the EPS, but the molecular mass of EPS decreased from 3.04×104 g/mol (without CSC) to 2.75×104 (with CSC). The SEC/MALLS also revealed the molecular conformation of EPS changed from flexible coil to globular shape in aqueous solution. Conclusion: This study revealed that CSC was directly able to affect molecular mass and structural conformation of EPS from S. mutans. The molecular characterization of EPS would become an indicator in certain pathological disorders.

Dietary flavonoid fisetin increases abundance of high-molecular-mass hyaluronan conferring resistance to prostate oncogenesis.

We and others have shown previously that fisetin, a plant flavonoid, has therapeutic potential against many cancer types. Here, we examined the probable mechanism of its action in prostate cancer (PCa) using a global metabolomics approach. HPLC-ESI-MS analysis of tumor xenografts from fisetin-treated animals identified several metabolic targets with hyaluronan (HA) as the most affected. Efficacy of fisetin on HA was then evaluated in vitro and also in vivo in the transgenic TRAMP mouse model of PCa. Size exclusion chromatography-multiangle laser light scattering (SEC-MALS) was performed to analyze the molar mass (Mw) distribution of HA. Fisetin treatment downregulated intracellular and secreted HA levels both in vitro and in vivo Fisetin inhibited HA synthesis and degradation enzymes, which led to cessation of HA synthesis and also repressed the degradation of the available high-molecular-mass (HMM)-HA. SEC-MALS analysis of intact HA fragment size revealed that cells and animals have more abundance of HMM-HA and less of low-molecular-mass (LMM)-HA upon fisetin treatment. Elevated HA levels have been shown to be associated with disease progression in certain cancer types. Biological responses triggered by HA mainly depend on the HA polymer length where HMM-HA represses mitogenic signaling and has anti-inflammatory properties whereas LMM-HA promotes proliferation and inflammation. Similarly, Mw analysis of secreted HA fragment size revealed less HMM-HA is secreted that allowed more HMM-HA to be retained within the cells and tissues. Our findings establish that fisetin is an effective, non-toxic, potent HA synthesis inhibitor, which increases abundance of antiangiogenic HMM-HA and could be used for the management of PCa.

Acid-thinned corn starch-impact of modification parameters on molecular characteristics and functional properties

Acid-thinned corn starches were prepared systematically by varying acid concentrations (0.09–0.72 M HCl) and hydrolysis times (4 and 24 h). The relationships between modification parameters, molecular starch structure, and functional properties were investigated. The carbohydrate solubilization was significantly enhanced with increasing acid concentration only in the long-term process. SEM micrographs revealed the preservation of the granular structure and the thermal properties changed only moderately applying different hydrolysis conditions. Molecular characterization using SEC-MALS (size exclusion chromatography-multi angle laser light scattering) showed a strong degradation of amylopectin after 4 h of hydrolysis. Enzymatic debranching prior to the analysis and separation of the amylose peak using deconvolution enabled the calculation of MMD curves of the acid-thinned amylose fraction. The data gave evidence of extensive molecular degradation of the amylose with increasing acid concentration when hydrolyzed for 24 h. The hot paste viscosity decreased with decreasing Mw and the sol-to-gel-transition temperature was found to be strongly dependent on both, the Mw of the starch as well as the amylose fraction. The correlation between molecular properties and gel strength gave evidence of an optimum degree of hydrolysis. Acid-thinning of the starch to Mw of about 12 · 106–8 · 106 g · mol−1 and 3 · 105–2.5 · 105 g · mol−1 for the amylose fraction, respectively, resulted in the highest gel strength within the present study. However, differences in gel strength had only marginal impact on the gel elasticity. The peak separation permitted a comprehensive and detailed characterization of the amylose fraction. The obtained data proved the exposed role of the amylose in the gelation process of acid-thinned starches and their gel firmness. Correlations between the modification process, the molecular starch structure, and resulting functional properties were found.

Thermal degradation of high molar mass hyaluronan in solution and in powder; comparison with BSA

The aim of the present work was to compare the thermal degradation of bovine serum albumin and hyaluronic acid of different molar masses by determining the loss in molecular weight by means of SEC-MALLS (size exclusion chromatography – multi angle laser light scattering). For all measured samples, the results obtained by this method were compared with the results for stability determined by electrophoretic light scattering. The degradation study was performed in solution and in powder.Bovine serum albumin (also known as BSA) is a protein derived from cows, which has many biochemical applications. Hyaluronic acid (hyaluronan or HA) is an anionic nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues.The powder and solutions of BSA and HA were heated at different temperatures ranging from 37 °C to 120 °C for certain periods (the highest temperature was used only for the powder). The observed degradation increased with the duration of heating and with temperature for all hyaluronic acid samples analyzed in this work, in accord with Arrhenius law.At 37 °C and 60 °C, only moderate degradation was observed for hyaluronic acid solutions. For BSA at 37 °C no degradation was observed and at 60 °C significant aggregation occurred.

Molecular characterization of acid‐thinned wheat, potato and pea starches and correlation to gel properties

Molecular parameters and gel properties of systematically prepared acid‐thinned starch products (wheat, potato, and pea) were investigated. The impacts of acid type (HCl, H2SO4), acid concentration (0.36 and 0.72 N), and hydrolysis time (4 and 24 h) were found to be statistically significant on weight‐average molar mass (Mw) of the starch as revealed by analysis of variance (ANOVA). Especially for potato starch samples, the blue value (BV) was found to increase after short‐time hydrolysis and decrease after longer modification, indicating a reduced amount of polysaccharide chains able to complex with iodine, which was found for all products. Simultaneously, the wavelength of the absorption maximum (λmax) decreased systematically with an increasing degree of modification, giving evidence for decreasing length of linear polymer chains. Enzymatic debranching of amylopectin and dextrins and molecular characterization by means of size exclusion chromatography‐multi angle laser light scattering (SEC‐MALS) enabled the detection of Mw and the amount of amylose fraction. Generally, declining Mw of amylose was accompanied by a mass‐specific loss. Starch pastes with very good solution states were prepared in general. Pastes of the acid‐thinned starches showed dominant viscous behavior, whereat storage and loss modulus decreased with increasing degradation. Additionally, a significant reduction of the sol‐to‐gel‐transition temperature was found applying oscillation measurements. Increasing gel strength of the starch samples was detected due to acid‐thinning up to a certain degree of modification and optimal molecular parameters of the starch as well as the amylose fraction were determined resulting best strength properties. The gel clarity was reduced due to acid modification in general.

Molecular mass and molecular-mass distribution of TEMPO-oxidized celluloses and TEMPO-oxidized cellulose nanofibrils.

Native wood cellulose was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, and the fibrous TEMPO-oxidized celluloses (TOCs) thus obtained were disintegrated in water to prepare TOC nanofibrils (TOCNs). The carboxyl groups of TOCs and TOCNs were methyl-esterified, and the methylated samples were dissolved in 8% LiCl/N,N-dimethylacetamide for size-exclusion chromatography/multiangle laser-light scattering (SEC-MALLS) analysis to obtain their molecular-mass (MM) values and MM distributions (MMDs). The results showed that remarkable depolymerization occurred in TOCs and TOCNs and depended on the oxidation and sonication conditions. Because single peaks without bimodal patterns were observed in the MMDs for all of the TOC and TOCN samples, depolymerization may have randomly occurred on whole cellulose molecules and oxidized cellulose molecules in the microfibrils during these treatments. Compared with the MM values obtained by SEC-MALLS, the intrinsic viscosities of TOCs dissolved in 0.5 M copper ethylenediamine solution provided lower MM values owing to depolymerization during the dissolution and postreduction processes.

Differential analysis on precise determination of molecular weight of triblock copolymer using SEC/MALS and MALDI-TOF MS

Precise determination of the molecular weight of a poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer (PEG-PTHF-PEG) using size-exclusion chromatography/multi-angle laser light scattering (SEC/MALS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) was carefully investigated. The potential uncertainty factors for both SEC/MALS and MALDI-TOF MS were evaluated using cause-effect diagrams. The consistency of data between the two methods was then assessed by t-test. It was found that the data from SEC/MALS and MALDI-TOF MS were not consistent. For clarifying the differential results, titration was also employed to further measure the molecular weight of triblock copolymer. The result indicated that the data from titration was consistent with that of SEC/MALS, but not consistent with the data from MALDI-TOF MS. The result of MALDI-TOF MS was smaller and showed a deviation of about 10% from the SEC/MALS result. The reason for this difference was then further explored.

Acid modification of wheat, potato, and pea starch applying gentle conditions—impacts on starch properties

Acid‐thinned wheat, potato, and pea starch products were systematically prepared applying gentle conditions with variation of acid type (HCl and H2SO4), acid concentration (0.36 and 0.72 N in a 40% (w/w) suspension) as well as hydrolysis time (4 and 24 h). Starch granule properties as well as molecular and rheological characteristics in the solution state were analyzed and the impact of all parameters varied was found to be immense. Carbohydrate solubilization of wheat and potato starch was significantly higher compared to pea starch. Noteworthy progress in solubilization was found when hydrolyzed with HCl, and with increasing acid concentration and increasing hydrolysis time by trend. The hydrolysis affected the reduction of the hot paste viscosity most dominant in the first period of treatment (0–4 h), however, size exclusion chromatography‐multi angle laser light scattering (SEC‐MALS) analysis revealed a more prominent molecular degradation during the second period (4–24 h). This observation led to the interpretation that the molecular degradation in the initial phase results particularly in “debranching” of the high molar mass amylopectin fraction and lower hot paste viscosity. Continued hydrolysis with significant reduction of the molecular size, however, had reduced impact on further lowering of viscosity. SEM micrographs displayed intact pea starch granules with unchanged surface after hydrolysis, whereas wheat and potato starch granules were visibly affected with damage not evenly distributed but a variation over the granule population. Granular wheat and potato starch exhibited significantly enhanced particle size after short period modification measured in water. However, this was found eliminated at extended hydrolysis time. Reasons were hydrolysis induced molecular rearrangement resulting in better crystalline packing on the amorphous/crystalline threshold reducing the ability to swell, and the progress in granular erosion. That was in line with changed swelling characteristics determined using DSC. The study gave evidence for strong impact of acid hydrolysis on functional properties like water binding.

Characterization and antioxidant activity for exopolysaccharide from submerged culture of Boletus aereus

Three polysaccharide fractions (designated as Fr-I, Fr-II and Fr-III) were successfully purified from the crude exopolysaccharide (EPS) produced from submerged culture of Boletus aereus by gel filtration chromatography on Sepharose CL-6B. The size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) system showed that the average molecular weights (Mws) of these three fractions were 1.365×106, 1.048×105 and 2.471×104g/mol, respectively. The SEC/MALLS also revealed that the molecular conformation of the Fr-I was a random coil, with Fr-II being a rigid rod in aqueous solution. Moreover, monosaccharide composition analysis indicated that Fr-I was mainly composed of glucose, while both of Fr-II and Fr-III were mainly composed of mannose and glucose. Then, FT-IR spectral analysis of the purified EPS revealed prominent characteristic groups. Furthermore, thermo gravimetric analysis (TGA) indicated the degradation temperature of the Fr-I (170°C) was higher than those of Fr-II (156°C) and Fr-III (155°C). Finally, on the basis of the antioxidant activity test in vitro, Fr-I exhibited the highest antioxidant ability among these samples, which might be attributed to the monosaccharide composition and molecular weight in the EPS fraction.

Effects of specific mechanical energy on soy protein aggregation during extrusion process studied by size exclusion chromatography coupled with multi-angle laser light scattering

The effects of specific mechanical energy (SME) on soy protein aggregation during extrusion process were studied using a combination of size exclusion chromatography, multi-angle laser light scattering (SEC-MALLS) and dynamic light scattering. Results showed that the weight-average molecular weights (Mw) of soy protein isolate (SPI) and those of the aggregates increased 74–104% and 39–67%, respectively after the extrusion treatments. However, they decreased from 2.688 to 2.340×106g/mol and from 1.115 to 0.926×107g/mol, respectively when SME increased from 839.81 to 1277.01kJ/kg. The increasing SME caused the proportion increase of low molecular weight fractions from 35.02% to 52.63% as well. It was concluded that protein was disassociated/depolymerized by mechanical shear during the extrusion process, and the increasing SME could enhance the extent of breakdown of protein aggregates. There existed vital factors contributing to the aggregation of proteins, and more information of the vital factors needs to be further investigated.