Association under shear flow in aqueous solutions of pectin

Shear, extensional rheology, and tribology of polysaccharide-thickened soy protein-based liquid systems for dysphagia management

Modifying food texture is a valuable approach to enhancing the quality of life for patients with dysphagia. Incorporating thickened soy protein-based liquid systems (SPLS) into their diet not only improves protein intake but also promotes safer swallowing. However, the properties of thickened SPLS are crucial for safe swallowing, may vary depending on the conformation of the thickened polysaccharides used. In this study, SPLS with different levels of thickening were prepared using xanthan gum, pectin and guar gum. The influence of polysaccharide conformation on the rheological (shear and extensional) and tribological properties of thickened SPLS was investigated. The results revealed that xanthan gum-thickened SPLS exhibiting the highest shear viscosity (110.073 Pa.s) and extensional viscosity (7.405 Pa.s), which increased with polysaccharide concentration. Meanwhile, xanthan gum possessed the strongest lubricating properties. These results shed light on the development of plant protein-based solutions for dysphagia management.

Self-healing injectable hydrogels incorporating hyaluronic acid and phytic acid: Rheological insights and implications for regenerative medicine

Eying the increasing impact of hyaluronic acid (HA) and its multifaceted applications, this study employs a non-toxic, one-pot strategy to develop injectable, self-healing hydrogels for biomedical applications. Phytic acid (PA), a plant-derived organic acid with high biocompatibility and numerous hydroxyl groups, can act as a cross-linking agent to form hydrogen-bonded networks with the HA chains. The study examined the optimal mass ratio of HA to PA to achieve superior hydrogel performance. Fourier transform infrared spectroscopy, rheological studies, and thermal analysis confirmed the successful formation of the hydrogels, which exhibited injectability, rapid self-healing, malleability, and elasticity. The investigation of different compositions revealed a sensitive influence of PA on the self-assembly phenomena of HA during flow. SEM cross-section images of the freeze-dried gels revealed a porous surface in the form of an interconnected network of microchannels. In addition, the hydrogel exhibits good tissue adhesion properties and promotes cell proliferation in biocompatibility tests on human gingival fibroblasts. The significance of this study lies in the ability of the proposed materials to be injected, to conform to the complex 3D structure of host tissues as well as their ability to recover after damage, indicating significant potential as scaffolds for wound healing.

Sucrose and Ca2+ synergistically regulate the rheological properties of apple high-methoxyl pectin

The thickening and gelling mechanism of high-methoxyl pectins (HMPs) with different degree of esterification (DE) values (60.6 %, 66.1 %, and 72.4 %) synergistically affected by calcium ion (Ca2+) and sucrose was investigated using several technical methods. Rheological measurements, including steady-shear flow, thixotropy and dynamic viscoelasticity tests, texture analysis, water-holding capacity (WHC), thermal analyses (TG), and microstructure observation (TEM), were all systemically conducted. The results showed that the main thickening and gelling mechanism of Ca2+ on different HMPs was complex and the presence of sucrose had a synergistic effect on structure formation in HMP systems. Ca2+ was not always conducive to structure formation, and excessive Ca2+ addition may hinder structure formation. HMP systems with lower DE values had higher gel strengths due to the presence of more binding domains. The results of the texture properties, WHC, and thermal characteristics coincided with those obtained from the rheological measurements, which reflect the variations in HMPs affected by Ca2+ and DE. All of these results showed that Ca2+ addition at an appropriate concentration in the presence of sucrose favors HMP gelation even in the absence of acid. The results obtained here are expected to broaden the application of HMPs in acid-free gel food products.

The effect of ultrasonic power on the physicochemical properties and antioxidant activities of frosted figs pectin

Ultrasound has been widely used in industry due to its high energy and efficiency. This study optimized the ultrasonic-assisted extraction (UAE) process of frosted figs pectin (FFP) using response surface methodology (RSM), and further investigated the effect of ultrasonic power on the structural characteristics and antioxidant activities of FFPs. The UAE method of FFP through RSM was optimized, and the optimal extraction process conditions, particle size of 100 mesh, pH value of 1.95, liquid-solid ratio of 47:1 (mL/g), extraction temperature of 50 °C and extraction time of 65 min, were obtained. The extraction rate of FFP under this condition was 37.97 ± 2.56 %. Then, the four FFPs modified by ultrasound were obtained by changing the ultrasonic power. Research had found that ultrasonic power had little effect on the monosaccharide composition, Zeta potential, as well as the thermal stability and appearance structure of the four FFPs. However, ultrasonic power had a significant impact on other properties of FFP: as the ultrasonic power increased, the DM% and particle size decreased continuously, while the total carbohydrate content increased. Meanwhile, ultrasonic power also had a significant impact on antioxidant activities of FFPs. From the research results, it could be seen that different ultrasonic power had certain changes in its spatial structure and properties, and the structural changes also affected the biological activity of FFP. The study of the effects of ultrasonic power on the physicochemical properties and biological activity of FFP lays the foundation for the development and application of FFP in food additives and natural drug carriers.

Does harvesting age matter? Changes in structure and rheology of a shear-thickening polysaccharide from Cyathea medullaris as a function of age

A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of -4)-β-D-GlcpA-(1 → 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.

Pectin-rich dragon fruit peel extracts: An environmentally friendly emulsifier of natural origin

Pectin extraction is generally an energy-intensive industrial process, while on the other hand their extraction methods vary from different sources. Starting with that perspective, pectin (WSP) containing ultra-low degree of methylation (31.08 ± 1.27%) from dragon fruit peel (DFP) was extracted by using pure water at room temperature. WSP, dominant in DFP (17.13 ± 1.01%), showed both a high molecular weight and a wide molecular weight distribution, while the yield of the rest acid-soluble pectin (HAP) from DFP residue was only 5.22 ± 0.76%. Furthermore, WSP can stabilize emulsions over a wide range of concentrations and oil phases, especially HIPE. Therefore, the hypothesis was verified that the pectin-rich extract from dragon fruit peel with excellent emulsifying properties could be simply extracted by pure water. This environmentally-friendly and energy-saving extraction method provides a new insight to increase the additional value of dragon fruit peel produced in food processing.

TLR 2/1 interaction of pectin depends on its chemical structure and conformation

Citrus pectins have demonstrated health benefits through direct interaction with Toll-like receptor 2. Methyl-ester distribution patterns over the homogalacturonan were found to contribute to such immunomodulatory activity, therefore molecular interactions with TLR2 were studied. Molecular-docking analysis was performed using four GalA-heptamers, GalA₇Me⁰, GalA₇Me^1,6, GalA₇Me^1,7 and GalA₇Me^2,5. The molecular relations were measured in various possible conformations. Furthermore, commercial citrus pectins were characterized by enzymatic fingerprinting using polygalacturonase and pectin-lyase to determine their methyl-ester distribution patterns. The response of 12 structurally different pectic polymers on TLR2 binding and the molecular docking with four pectic oligomers clearly demonstrated interactions with human-TLR2 in a structure-dependent way, where blocks of (non)methyl-esterified GalA were shown to inhibit TLR2/1 dimerization. Our results may be used to understand the immunomodulatory effects of certain pectins via TLR2. Knowledge of how pectins with certain methyl-ester distribution patterns bind to TLRs may lead to tailored pectins to prevent inflammation.

Chain conformations and steady-shear viscosity properties of pectic polysaccharides from apple and tomato

In this study, apple pectin (AP) and tomato pectin (TP) were demonstrated to be a high-ester (74.8%) polysaccharide with the weight-average molecular weight (Mw ) of ∼ 243 kDa and a low-ester (45.9%) polysaccharide with the Mw of ∼ 19 kDa, respectively. The semi-rigid chain conformations of pectic polysaccharides in NaNO3 aqueous solution were deduced according to the Smidsrød "B values" of AP (0.025) and TP (0.029), while AP and TP exhibited higher stiffness in water due to the electric repulsion of carboxyl groups, which was visually observed by AFM images. Under steady shear, the shear-thickening behaviors of AP and TP in NaNO3 aqueous solutions were observed in the shear rate range of < 1 s-1, which were attributed to the disruption of the ordered arrangement induced by semi-rigid pectin chains into randomly entangled structure by weak shear force. AP exhibited stronger shear-thickening behavior due to the formation of more entanglements resulted from the higher Mw and longer side chains highly branched at rhamngalacturonan region. This study provides the scientific basis for the construction of the relationship of steady-shear property with chain conformation and molecular weight of pectin.

Polysaccharide-Zein Composite Nanoparticles for Enhancing Cellular Uptake and Oral Bioavailability of Curcumin: Characterization, Anti-colorectal Cancer Effect, and Pharmacokinetics

Curcumin (CUR) has demonstrated promising potential as a therapeutic agent against colorectal cancer (CRC). However, its intrinsic shortcomings, including oxidative instability, sensitivity to gastrointestinal (GI) hydrolytic/enzymatic action, and susceptibility to biotransformation and systemic elimination, have greatly undermined its value for application in clinical settings. The development of carriers, in particular oral formulations, for its efficient delivery has remained an important direction in nutraceutical research. In the present work, CUR-encapsulated nanoparticles were fabricated with zein alone (Zein-CUR) and with zein and a polysaccharide (PS) [gum Arabic (GA), hyaluronic acid (HA) and pectin (PC), respectively] (PS-Zein-CUR). Their physicochemical and biological properties were evaluated in a series of in vitro and in vivo assays. Dynamic light scattering analysis showed an increase in the particle size of the nanoparticles from 129.0 nm (Zein-CUR) to 188.8-346.4 nm (PS-Zein-CUR). The three PS-Zein-CUR formulations had significantly higher (17-22%) CUR encapsulation efficiency (EE) than Zein-CUR. Among them, HA-Zein-CUR exhibited the highest EE and loading capacity. Zeta potential and FTIR spectra indicated the involvement of electrostatic and hydrophobic interactions and hydrogen bonds in the formation of the PS-Zein-CUR. In human CRC cell lines (HCT8, HCT29, and HCT116), the three PS-Zein-CUR and CUR all effectively inhibited cell viability and colony formation (HA-Zein-CUR > PC-Zein-CUR > GA-Zein-CUR/CUR). HA-Zein-CUR and PC-Zein-CUR also resulted in significantly higher cellular uptake of CUR than GA-Zein-CUR and CUR. Simulated GI-digestion assay demonstrated significantly improved controlled-release properties of these two formulations. Further pharmacokinetics and tissue distribution assays in a CRC subcutaneous xenograft model in nude mice corroborated the enhanced pharmacokinetic properties of intragastric administration of HA-Zein-CUR compared with that of free CUR (3 times higher C max and 9.18 times higher plasma AUC). HA-Zein-CUR also led to enhanced delivery and accumulation of CUR in major organs/tissues, in particular CRC tumors and colon. These results together support that HA-Zein-CUR has promising potential as an oral agent for the control of CRC.

Optimization of substrate composition for pectinase production from Satkara (Citrus macroptera) peel using Aspergillus niger-ATCC 1640 in solid-state fermentation

Pectinase is an enzyme having a broad industrial and commercial application. However, higher production costs may be the major constraint for the wide-scale application of pectinase. Therefore, researchers are trying to reduce the pectinase production cost for subsequent application in the industrial processes by using a unique substrate and optimizing the fermentation medium components and process conditions. The main purpose of the current study was to optimize medium composition for pectinase production using Aspergillus niger-ATCC 1640 in the solid-state fermentation. The Response Surface Methodology (RSM) was performed to evaluate the effects of variables, specifically the concentrations of Satkara peel, urea, (NH₄)₂PO₄, NH₄NO₃, KH₂PO₄, ZnSO₄, and MgSO₄.7H₂O on pectinase production in the solid substrate. Firstly, a two-factorial design, Plackett-Burman design (PBD) was applied to screen the variables that significantly influenced the pectinase production. After finding the critical variables, 15 experimental runs were carried out using a Box-Behnken design (BBD) to derive a statistical model for optimizing the concentrations of the selected variables. The PBD model revealed that Satkara peel, urea, and (NH₄)₂SO₄ significantly affected the pectinase production. RSM results indicated that the predicted response for pectinase production was in good agreement with experimental data (R² = 0.9836). Under the optimized condition of Satkara peel (8.4 g/L), urea (0.5 g/L), and (NH₄)₂SO4 (2.7 g/L), the pectinase activity was predicted to be 0.6178 μmol/mL. In the present study, the experimental pectinase production achieved 0.6045 μmol/mL. The study revealed that optimization through RSM could improve the pectinase production from Satkara peel.

Ultrasound freeze-thawing style pretreatment to improve the efficiency of the vacuum freeze-drying of okra (Abelmoschus esculentus (L.) Moench) and the quality characteristics of the dried product

Vacuum freeze-drying is a new and high technology on agricultural product dehydrating dry, but it faces the high cost problem caused by high energy consumption. This study investigated the effect of ultrasound (US), freeze-thawing (including the freeze-air thawing (AT), freeze-water thawing (WT), freeze-ultrasound thawing (UST), and freeze-air ultrasound thawing (AT + US)) pretreatments on the vacuum freeze-drying efficiency and the quality of dried okra. The results indicated that the application of ultrasound and different freeze-thawing pretreatments reduced the drying time by 25.0%-62.50% and the total energy consumption was 24.28%-62.35% less. The AT pretreatment reduced the time by of okra slices by 62.50% and the total energy consumption was 62.35% less. The significant decrease in drying time was due to a change in the microstructure caused by pretreatment. Besides, the okra pretreated with the US retained most of the quality characteristics (flavor, color, hardness, and frangibility) among all methods, while, AT + US had the most changeable characteristics in quality, which is deprecated in our study. The okra pretreated with the US and AT, separately, had the best dry matter content loss (9.008%, 5.602%), lower chlorophyll degradation (5.05%, 5.44% less), and higher contents of total phenolics, total flavonoids, and pectin, with strong antioxidant capacity, compared to other methods. The pretreatments did not have a large effect on the functional groups and the structure of pectin, but slightly affected the viscosity. It can be concluded that AT and US pretreatment methods are better than others.

Hydrophobized cellulose nanocrystals enhance xanthan and locust bean gum network properties in gels and emulsions

Locust bean/xanthan gum (LBG/XG) synergistic networks have previously been well studied, with evidence that junction zones between the two polymers result in hydrophobic domains. Here we report on the effect of both hydrophilic and hydrophobic cellulose nanocrystals (CNCs) on the rheological properties of the individual gums, the gum networks, and emulsion gels consisting of the gum network and corn oil. We also take advantage of differences in the autofluorescent spectra for each of the components to map their distribution within the gel and emulsion gel systems. Whilst both types of CNC confer thermal stability to the systems, hydrophilic CNCs induce minor changes in rheological properties of synergistic gels and prove to be detrimental to the stability of the emulsion gels. In contrast, hydrophobic CNCs associate with the LBG/XG network, affecting the rheological response. Their inclusion in the emulsion gel system results in smaller, more homogeneously distributed oil droplets with a resultant increase in the storage modulus by an order of magnitude compared to the CNC-free and hydrophilic CNC systems. We conclude that hydrophobic CNCs play a critical role in stabilising LBG/XG network gels and emulsions.

Physicochemical and rheological characterization of pectin-rich polysaccharides from Gardenia jasminoides J. Ellis flower

Gardenia (Gardenia jasminoides J. Ellis) is regarded as an edible medicine plant in China. Here, gardenia flower polysaccharide fraction (GFPF) was extracted by water at 90°C and its chemical composition, rheological properties, and antioxidant activities of GFPF were investigated. The GFPF extraction yield was 18.04 ± 1.81% (W/W) and mainly comprised neutral sugars (46.83 ± 3.14%), uronic acid (35.21 ± 0.17%), protein (1.63 ± 0.34%), and total phenol (9.49 ± 0.08 mgGAE/g). Galacturonic acid (41.05 ± 0.59%) was the main monosaccharide, and galactose, glucose, arabinose, rhamnose, xylose, mannose, and glucuronic acid were also detected in GFPF. Its degree of esterification was 32.76 ± 1.52%. FT-IR spectra analysis showed a similar absorption pattern between GFPF and pectin from apple. The results suggested that GFPF was low methoxy pectin. Thermogravimetric analysis and zeta potential analysis indicated that the pectin was stable under high temperature and alkaline condition. Steady rheology showed that the GFPF dispersion was a shear thinned pseudoplastic fluid with high apparent viscosities at concentration above 2%. The degree of pseudoplasticity of the solutions increased with the concentrations increased and the temperatures decreased. DPPH and ABTS free radical scavenging assay indicated that GFPF had relatively high antioxidant activity. The results showed that gardenia flower was rich in pectin polysaccharides with low methoxy pectin. It had high apparent viscosities at concentration above 2% and had good antioxidant activity. The data suggested that GFPF can be a new resource of low methoxy pectin with potential application as thicker or gelling agents in food industry.

Physicochemical and rheological characterization of pectin-rich fraction from blueberry (Vaccinium ashei) wine pomace

Blueberry wine pomace is rich in pectin, which has been extensively used as a functional dietary fiber and a rheological modifier in the food industry. This paper reports a method to extract the pectin-rich fraction (PF) with a mediate degree of esterification of 51.66% from blueberry wine pomace and provides insight into its relationship between the structure and rheological properties. The impacts of related extrinsic factors, such as sucrose, ions and pH, were also studied in view of food applications. The viscosity of PF aqueous dispersion gradually increased with its concentration. The addition of sucrose, CaCl₂ or NaCl to the solution resulted in increased viscosity. However, the elevations in temperature and pH led to decrease in solution viscosity. The viscoelastic property of PF dispersion displayed strong temperature dependence but weak frequency dependence. This was largely due to PF concentration, sucrose, CaCl₂ and solution pH. The present study revealed the unique characteristic of medium-methoxylated pectin fraction and the obtained results are helpful in value-added utilization of blueberry wine pomace.

Exploring the relationship between nanoscale dynamics and macroscopic rheology in natural polymer gums

We report a study connecting the nanoscale and macroscale structure and dynamics of Acacia mearnsii gum as probed by small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS) and rheology. Acacia gum, in general, is a complex polysaccharide used extensively in industry. Over the analyzed concentration range (15 to 30 wt%) the A. mearnsii gum is found to have a gel-like linear rheology and to exhibit shear thinning flow behavior under steady shear. The gum solutions exhibited a steadily increasing elastic modulus with increasing time after they were prepared and also the emergence of shear thickening events within the shear thinning behavior, characteristic of associative polymers. XPCS measurements using gold nanoparticles as tracers were used to explore the microscopic dynamics within the biopolymer gels and revealed a two-step relaxation process with a partial decay at inaccessibly short times, suggesting caged motion of the nanoparticles, followed by a slow decay at later delay times. Non-diffusive motion evidenced by a compressed exponential line shape and an inverse relationship between relaxation time and wave vector characterizes the slow dynamics of A. mearnsii gum gels. Surprisingly, we have determined that the nanometer-scale mean square displacement of the nanoparticles showed a close relationship to the values predicted from the macroscopic elastic properties of the material, obtained through the rheology experiments. Our results demonstrate the potential applicability of the XPCS technique in the natural polymers field to connect their macroscale properties with their nanoscale structure and dynamics.

Faba bean hulls as a potential source of pectin

This study aimed for the first time to assess the potential use of faba bean hulls as a source of pectin. The study involved extracting pectin under various conditions of pH, temperature and extraction time and determining how these conditions affected pectin yield and its characteristics. The maximum yield of extracted pectin did not coincide with the highest degree of esterification since the maximum yield (15.75 %) was recorded at pH 1.5 and at a temperature of 85 °C for an 80-min extraction period and solid to liquid (1: 25) ratio, while the highest degree of esterification (54.62 %) occurred at pH 2.5 and at temperature of 90 °C for a 60-min extraction period. The composition of the pectin varied according to the extraction conditions: the neutral sugars galactose, arabinose and rhamnose increased under milder extraction conditions while glucose, mannose and xylose sugars predominated under harsher extraction conditions. The results indicated that faba bean hulls contains adequate amount of pectin, suitable for commercial utilization.

Synthesis, characterization, and cellular uptake of magnetic nanocarriers for cancer drug delivery

HYPOTHESIS

The absence of targetability is the primary inadequacy of conventional chemotherapy. Targeted drug delivery systems are conceptualized to overcome this challenge. We have designed a targetable magnetic nanocarrier consisting of a superparamagnetic iron oxide (SPIO) core and biocompatible and biodegradable poly(sebacic anhydride)-block-methyl ether poly(ethylene glycol) (PSA-mPEG) polymer shell. The idea is that this type of carriers should facilitate the targeting of cancer cells.

EXPERIMENTS

PSA-mPEG was synthesized with poly-condensation and the in vitro degradation rate of the polymer was monitored by gel permeation chromatography (GPC). The magnetic nanocarriers were fabricated devoid of any surfactants and were capable of carrying high payload of hydrophobic dye. The successful encapsulation of SPIO within the polymer shell was confirmed by TEM. The results we obtained from measuring the size of SPIO loaded in polymeric NPs (SPIO-PNP) by dynamic light scattering (DLS) and iron content measurement of these particles by ICP-MS, indicate that SPIO is the most suitable carrier for cancer drug delivery applications.

FINDINGS

Measuring the hydrodynamic radii of SPIO-PNPs by DLS over one month revealed the high stability of these particles at both body and room temperature. We further investigated the cell viability and cellular uptake of SPIO-PNPs in vitro with MDA-MB-231 breast cancer cells. We found that SPIO-PNPs induce negligible toxicity within a concentration range of 1-2μg/ml. The TEM micrographs of thin cross-sectioned MDA-MBA-231 cells showed internalization of SPIO-PNPs within size range of 150-200nm after 24h. This study has provided a foundation for eventually loading these nanoparticles with anti-cancer drugs for targeted cancer therapy using an external magnetic field.

Potential utilization of Citrullus lanatus var. Colocynthoides waste as a novel source of pectin

The Citrullus lanatus var. Colocynthoides is an ancestor type of watermelon. It was investigated as a new source of pectin. It was cultivated in Egypt for seeds only, while the remaining fruits are discarded as waste. Effect of different extraction conditions such as pH, solid: liquid ratio, temperature and extraction time on pectin yield of Citrullus lanatus var. Colocynthoides waste was investigated in the present study. The highest yield (19.75 % w/w) was achieved at pH 2, solid: liquid ratio1:15 and 85 °C, for 60 min. Methylation degree and galacturonic acid content of extracted pectin were 55.25 %, w/w and 76.84 %, w/w. The main neutral sugars were galactose followed by arabinose and rhamnose. In addition, glucose, xylose and mannose existed as constituents in the pectin hydrolysate. The results indicated that Citrullus lanatus var. Colocynthoide waste is a potential new source of pectin.

Microfluidic formulation of pectin microbeads for encapsulation and controlled release of nanoparticles

We report a method for formulation of pectin microbeads using microfluidics. The technique uses biocompatible ingredients and allows for controlled external gelation with hydrogen and calcium ions delivered from an organic phase of rapeseed oil. This method allows for encapsulation of nanoparticles into the microparticles of gel and for control of the rate of their release.

Characterization of polyelectrolyte features in polysaccharide systems and mucin

This review elucidates several aspects on the behavior of charged polysaccharides and mucin. Viscosification of dilute aqueous solutions of hyaluronan (HA) occurs in the course of time at low shear flow, whereas shear thinning as time evolves is found at moderate shear rates. Hydrogen bonds and electrostatic interaction play an important role for the emergence of these features. No time effect of the viscosity is observed for semidilute HA solutions. A degradation of HA is observed at low and high pH and this effect continues over long times, and it is only in the approximate interval 5<pH<10 that HA is stable. Small angle neutron scattering (SANS) measurements on semidilute aqueous solutions of mucin at pH=7 reveal a fractal dimension of 1.4, and the effect of temperature is insignificant on the fractal structure. This suggests that the mucin chains on a semi-local dimensional scale are rod-like. From various experimental methods on solutions of mucin it was found that at pH values around 2 (uncharged polymer), the intensive hydrophobic interactions lead to large association complexes, whereas at pH>>2 the negative charges suppress the tendency of forming associations. At pH<2, the mucin chains are compressed and they are decorated by some positive charges. In the semidilute regime, a fragmented network is developed. The intense association in semidilute solutions of mucin at pH=2 is further supported by the results from rheo-small angle light scattering measurements. Effects of ionic strength on the radius of gyration (R(g)) for dilute solutions of HA (pH=7) and positively charged hydroxyethylcellulose (HEC(+)) are studied with the aid of Monte Carlo simulations, and essential features of the polyelectrolyte effect on R(g) are captured in the computer simulation. Strong interactions are observed in aqueous mixtures of an anionic polysaccharide (HEC(-)) and an oppositely charged surfactant (cetyltrimethylammonium bromide; CTAB); this gives rise to extensive associations and macroscopic phase separation is approached. The massive association complexes are disclosed in the SANS experiments by a pronounced upturn in the scattered intensity at low values of the wave vector.