Formation of fibrous materials from dense calcium caseinate dispersions

Application of shear and cross-linking enzyme transglutaminase (Tgase) induced fibrous hierarchical structures in dense (30% w/w) calcium caseinate (Ca-caseinate) dispersions. Using Tgase was essential for the anisotropic structure formation. The fibrous materials showed anisotropy on both micro- and macroscale as determined with scanning electron microscopy (SEM) and mechanical analyses, respectively. SEM revealed protein fibers with a diameter of approximately 100-200 nm; visually, we observed fibers of about 1 mm. Both shear and Tgase affected the reinforcement of the fibers to a large extent, whereas the mechanical properties in the direction perpendicular to the shear flow remained constant. Shearing Ca-caseinate without Tgase yielded a slightly anisotropic layered structure. Both cross-linking in the absence of shear and cross-linking during mixing resulted in gels without alignment. The formation of shear- and enzyme-induced anisotropic structures was explained by aligning of protein aggregates due to shear and concurrent solidification of the aligned protein aggregates.     

Characterization of Aqueous Dispersions and Gels Made of Sodium Caseinate and Basil Seed Gum: Phase Behavior,Rheology, and Microstructure

The interactions between sodium caseinate (NaCas) and basil seed gum (BSG) in the presence of calcium chloride (CaCl₂) were investigated. The phase behavior of the mixed aqueous dispersions and their gels revealed a homogeneous mixture, obtained at the higher concentrations of both CaCl₂ and BSG. The Herschel-Bulkley model sufficiently fitted the flow behavior of the mixture solution data. Apparent viscosity increased significantly (p < 0.05) by increasing the concentration of BSG, where the addition of CaCl₂ had no significant effect on the viscosity of the samples (p > 0.05). Furthermore, there was an increase in thixotropy due to the higher concentrations of BSG and CaCl₂. Based on the frequency sweep test, at the low frequencies, a more gel-like behavior was observed in the case of the higher concentrations of either BSG or CaCl₂. The rheological and SEM data suggested that the stronger structure of NaCas-BSG gel in the presence of the higher concentrations of CaCl₂ was related to the induction of complex formation between the two biopolymers.

     

Influence of Extraction Method on the Rheological Properties of Jackfruit (<Emphasis Type="Italic">Artocarpus heterophyllus</Emphasis>) Seed Starch Dispersions

Starches are widely used in food processing, and their rheological properties are affected by thermal conditions imposed during the process. The objective of the present study was to assess the rheological behavior of jackfruit seed starch (JSS) dispersions, with a particular interest on the effects of the starch extraction techniques using either water or an alkali solution (0.1 M sodium hydroxide) as solvents. The analyses on the starches were performed using small amplitude oscillatory shear tests, including frequency, temperature, and time sweeps, and determining flow curves at different temperatures (10–40 °C). JSS dispersions were classified as weak-intermediary gels, and those prepared with JSS extracted with water showed higher values of G’ and G” in all of the tested samples. All gelatinized samples exhibited viscoelastic behavior, and with increasing temperatures the storage and loss moduli increased until a maximum value before reaching a plateau. Gelatinization temperatures were slightly lower for dispersions prepared with JSS extracted with water. Gelatinization kinetics showed that increasing temperatures caused a reduction in the time to achieve gelatinization. The JSS dispersions displayed thixotropic behavior, which was influenced by their concentration and the extraction method employed. The flow curves exhibited pseudoplastic behavior. The Power Law model was used to describe the JSS dispersions rheological behavior, which enabled to assess the effects of starch concentration and extraction method on their rheological properties.     

Shear characteristics, miscibility, and topography of sodium caseinate-monoglyceride mixed films at the air-water interface

In this contribution, we are concerned with the study of structure, topography, and surface rheological characteristics (under shear conditions) of mixed sodium caseinate and monoglycerides (monopalmitin and monoolein) at the air/water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy, BAM) techniques have been applied in this study to mixtures of insoluble lipids and sodium caseinate spread at the air-water interface. At a macroscopic level, sodium caseinate and monoglycerides form an heterogeneous and practically immiscible monolayer at the air-water interface. The images from BAM show segregated protein and monoglyceride domains that have different topography. At surface pressures higher than that for the sodium caseinate collapse, this protein is displaced from the interface by monoglycerides. These results and those derived from interfacial shear rheology (at a macroscopic level) appear to support the idea that immiscibility and heterogeneity of these emulsifiers at the interface have important repercussions on the shear characteristics of the mixed films, with the alternating flow of segregated monoglyceride domains (of low surface shear viscosity, etas) and protein domains (of high etas) across the canal.     

Creating Novel Structures in Food Materials: The Role of Well-Defined Shear Flow

Structure formation in food materials is influenced by the ingredient properties and processing conditions. Until now, small structural elements, such as fibrils and crystals, have been formed using self-assembly, while processing was applied to create relatively large structures. The effect of self-assembly under flow is rarely studied for food materials, but it is widely studied for non-food systems. The use of well-defined flow, often simple shear, turned out to be essential to study and control the structure formation process in foods as well. This observation encouraged us to develop a number of different shearing devices that allowed processing of biopolymer systems under simple shear flow. This paper reviews our main findings. In the case of protein fibrillization, the shear rate was found to control the growth rate as well as the properties of the fibrils formed. In the case of dough processing, simple shear flow made the product more process tolerant and induced gluten migration. The use of shear flow for dense caseinate dispersions led to hierarchically structured and fibrous material. Based on the presented results, we conclude that introducing simple shear flow in food structuring processes can lead to a much broader range of structures, thereby better utilizing the full potential of food ingredients.     

Rheological behavior of heated starch dispersions in excess water: role of starch granule

Granule size and size distribution, measured by laser diffraction, affected the flow behavior at 20 °C of (2.6% w/w) corn and cowpea starch dispersions heated for various time intervals above their gelatinization temperatures. The standard deviation of the granules' size described the transition of flow behavior from shear thickening in the early stages of gelatinization to shear thinning in the latter stages and influenced the critical shear rate, y_c, for the onset of shear thickening in starch dispersions. The granules swelled to a maximum of about 3.5 times the raw starch granule mean diameter and 65% granule mass fraction. The consistency index of the dispersions increased with granule mean diameter. Modified waxy maize starch dispersions heated at 80 °C exhibited antithixotropic behavior at a shear rate of 200s⁻¹; both dynamic frequency data and Cox-Merz plots revealed their gel-like behavior.     

Effect of Tween Emulsifiers on the Shear Stability of Partially Crystalline Oil-in-Water Emulsions Stabilized By Sodium Caseinate

We investigated the effects of Tween emulsifier fatty acid chain length on the shear stability and crystallization behavior of 35 wt% partially crystalline oil-in-water emulsions prepared with and without 1 wt% sodium caseinate. Emulsions containing sodium caseinate and Tween 20, 40, 60 or 80 varied in shear stability, degree of supercooling and crystallization behavior depending on the type and concentration of Tween as well as the presence of protein. Generally, emulsions containing the unsaturated emulsifier Tween 80 were the most shear sensitive followed by the saturated emulsifiers Tween 20, 40 and 60 in order of increasing fatty acid chain length. Long chain saturated Tween emulsifiers (40 and 60) improved shear stability regardless of whether sodium caseinate was present indicating that alone, these emulsifiers form more robust interfacial films compared to the saturated short chain length Tween 20 and Tween 80. In emulsions prepared with sodium caseinate, the degree of supercooling decreased and the crystallization rate diminished with increasing saturated fatty acid chain length but only negligible changes were found without sodium caseinate. Together, these findings indicate that long chain saturated Tween emulsifiers provide better emulsion stability regardless of the presence of sodium caseinate but with sodium caseinate, stability may also be affected by changes to fat crystallization. These novel findings provide guidance on how combinations of proteins and emulsifiers can be used to modify and control the stability of partially crystalline oil-in-water emulsions through their combined effects on the properties of the interfacial film and fat crystallization.     

Study of the Formation and Solution Properties of Worm-Like Micelles Formed Using Both N-Hexadecyl-N-Methylpiperidinium Bromide-Based Cationic Surfactant and Anionic Surfactant

The viscoelastic properties of worm-like micelles formed by mixing the cationic surfactant N-hexadecyl-N-methylpiperidinium bromide (C₁₆MDB) with the anionic surfactant sodium laurate (SL) in aqueous solutions were investigated using rheological measurements. The effects of sodium laurate and temperature on the worm-like micelles and the mechanism of the observed shear thinning phenomenon and pseudoplastic behavior were systematically investigated. Additionally, cryogenic transmission electron microscopy images further ascertained existence of entangled worm-like micelles.     

Formation of stable nanoparticles via electrostatic complexation between sodium caseinate and gum arabic

The formation of electrostatic complexes between sodium caseinate and gum arabic (GA) was studied as a function of pH (2.0-7.0), using slow acidification in situ with glucono-delta-lactone (GDL) or titration with HCl. The colloidal behavior of the complexes under specific conditions was investigated using absorbance measurements (at 515 or 810 nm) and dynamic light scattering (DLS). In contrast to the sudden increase in absorbance and subsequent precipitation of sodium caseinate solutions at pH < 5.4, the absorbance values of mixtures of sodium caseinate and GA increased to a level that was dependent on GA concentration at pH 5.4 (pH(c)). The absorbance values remained constant with further decreases in pH until a sudden increase in absorbance was observed (at pH(phi)). The pH(phi) was also dependent upon the GA concentration. Dynamic light scattering (DLS) data showed that the sizes of the particles formed by the complexation of sodium caseinate and GA between pH(c) and pH(phi) were between 100 and 150 nm and these nanoparticles were visualized using negative staining transmission electron microscopy (TEM). Below pH(phi), the nanoparticles associated to form larger particles, causing phase separation. zeta-Potential measurements of the nanoparticles and chemical analysis after phase separation showed that phase separation was a consequence of charge neutralization. The formation of complexes between sodium caseinate and GA was inhibited at high ionic strength (>50 mM NaCl). It is postulated that the structure of the nanoparticles comprises an aggregated caseinate core, protected from further aggregation by steric repulsion of one, or more, electrostatically attached GA molecules.     

Physicochemical and Rheological Characterization of Gum Tragacanth Exudates from Six Species of Iranian <Emphasis Type="Italic">Astragalus</Emphasis>

The flow behavior of six species of Iranian gum tragacanth dispersions was investigated at different temperatures and ionic strengths, within a concentration range (0.05–1.5% w/w) using a controlled shear rate rheometer. The steady shear measurements showed that all of the gum dispersions had shear-thinning natures. The power law model was used to describe the rheological properties of dispersions and Arrhenius model was used to evaluate the temperature effect. Composition analysis, surface tension measurement, particle size analysis, and color measurement of all the species were also carried out. The results indicated that the six species of gum tragacanth being studied in this paper exhibited significantly different physicochemical properties. Therefore, various species of gum tragacanth can be used instead of different hydrocolloids in a wide range of applications.     

Rheological evaluation of inter-grade and inter-batch variability of sodium alginate

Polymeric excipients are often the least well-characterized components of pharmaceutical formulations. The aim of this study was to facilitate the QbD approach to pharmaceutical manufacturing by evaluating the inter-grade and inter-batch variability of pharmaceutical-grade polymeric excipients. Sodium alginate, a widely used polymeric excipient, was selected for evaluation using appropriate rheological methods and test conditions. The materials used were six different grades of sodium alginate and an additional ten batches of one of the grades. To compare the six grades, steady shear measurements were conducted on solutions at 1%, 2%, and 3% w/w, consistent with their use as thickening agents. Small-amplitude oscillation (SAO) measurements were conducted on sodium alginate solutions at higher concentrations (4–12% w/w) corresponding to their use in controlled-release matrices. In order to compare the ten batches of one grade, steady shear and SAO measurements were performed on their solutions at 2% w/w and 8% w/w, respectively. Results show that the potential interchangeability of these different grades used as thickening agents could be established by comparing the apparent viscosities of their solutions as a function of both alginate concentration and shear conditions. For sodium alginate used in controlled-release formulations, both steady shear behavior of solutions at low concentrations and viscoelastic properties at higher concentrations should be considered. Furthermore, among batches of the same grade, significant differences in rheological properties were observed, especially at higher solution concentrations. In conclusion, inter-grade and inter-batch variability of sodium alginate can be determined using steady shear and small-amplitude oscillation methods.     

Chemical and rheological properties of an extracellular polysaccharide produced by the cyanobacterium Anabaena sp. ATCC 33047

The cyanobacterium (blue-green alga) Anabaena sp. ATCC 33047 produces an exopolysaccharide (EPS) during the stationary growth phase in batch culture. Chemical analysis of EPS revealed a heteropolysaccharidic nature, with xylose, glucose, galactose, and mannose the main neutral sugars found. The infrared (IR) spectrum of EPS showed absorption bands of carboxylate groups. The average molecular mass of the polymer was 1.35 MDa. Aqueous dispersions at EPS concentrations ranging from 0.2% to 0.6% (w/w) showed marked shear-thinning properties (power-law behavior). Linear dynamic viscoelastic properties showed that the elastic component was always higher than the viscous component. Viscous and viscoelastic properties demonstrated the absence of conformational changes within the concentration range studied. Stress-growth experiments revealed that 0.4% and 0.6% (w/w) EPS dispersions showed thixotropic properties. A detailed comparison of the linear dynamic viscoelasticity, transient flow, and decreasing shear rate flow curve properties was made for 0.4% (w/w) dispersions of xanthan gum (XG), Alkemir 110 (AG), and EPS. Viscoelastic spectra demonstrated that the EPS dispersion turned out to be more "fluidlike" than the AG and XG dispersions. The flow indexes indicated that the EPS dispersion was less shear-sensitive than that of XG, showing essentially the same viscosity, that is, >50 s(-1). The fact that viscosities of EPS and AG dispersions were not substantially different within the shear-rate range covered must be emphasized, in relation to EPS potential applications. The rheological behavior of EPS dispersions indicates the formation of an intermediate structure between a random-coil polysaccharide and a weak gel.     

The application of shear and extensional viscosity measurements to assess the potential of hylan in viscosupplementation

The shear and extensional viscosity characteristics have been compared for hyaluronan and two samples of a cross-linked derivative, hylan, of different molecular weights. While shear thinning behavior was observed for all systems in shear flow, strain thickening was observed in extensional flow for the relatively dilute systems. However, there was a progressive transition to shear thinning behavior as the polymer concentration was increased. It is evident from the results that the shear flow techniques alone provide an incomplete picture of the rheological properties of these materials and that extensional flow characteristics are potentially dominant. For example, at relatively high deformation rates of 500 s¹ and above, our results show that the extensional viscosities of aqueous solutions of the various polymers are at least two orders of magnitude greater than their corresponding shear flow viscosities. The incremental differences in viscosity with concentration increased with increasing molecular mass of the polymers and were greater in exensional flow than shear flow. These results demonstrate that the dynamic network structure formed by the higher molecular mass hylans offer potentially better physical and mechanical properties for viscosupplementation of diseased osteoarthritis joints compared with the parent hyaluronan.     

Rheological evidence of the gelation behavior of hyaluronan-gellan mixtures

It was found that solutions of calcium hyaluronate (CaHA) (0.1 to approximately 0.5 wt%) could form a gel by mixing with solutions of sodium type gellan (0.1 to approximately 0.5 wt%), although neither polymer by itself forms a gel at low concentrations (0.1 to approximately 0.5 wt% in this experiment). The rheological properties of CaHA-gellan mixtures were investigated by dynamic and steady shear measurements. Both storage shear modulus G' and loss shear modulus G' for CaHA-gellan mixtures increased with increasing time, and tended to an equilibrium value after 1 h. After reaching steady values of G' and G", the frequency dependence of G' and G' was observed. G' was always larger than G' in the accessible frequency range from 10(-2) to 10(2) rad/s. The effects of pH and calcium ions were examined. Gel formation of the mixtures was promoted by decreasing pH and adding from 0.01 to 0.1 M calcium ions, but excessive calcium ions weakened the gel.     

Rheological,Mass Transfer,and Mixing Characterization of Cellulase-Producing Trichoderma reesei Suspensions

Steady and dynamic shear measurements are utilized to characterize the rheological behavior of Trichoderma reesei RUT-C30 fungal suspensions during batch growth on xylose (soluble substrate) or cellulose (particulate solid substrate) at three different fermentor impeller speeds (250, 400, and 550 rpm). Biomass concentrations versus time were unimodal on xylose and bimodal on cellulose. This behavior is consistent with relatively rapid, early growth on easily metabolized growth medium components (yeast extract), followed by a second, slower growth phase due to hydrolysis of recalcitrant cellulose by increasing cellulase concentrations. Critical dissolved oxygen (DO) concentration for T. reesei growth on cellulose was found to be 0.073 mmol/L. The DO was kept above this level by supplementing the air feed with pure oxygen, implying that mass transfer limitations were not the cause of bimodal cell growth. Steady shear rheological data showed shear thinning behavior and a yield stress for all broth samples regardless of substrate. Casson and Herschel−Bulkley constitutive equations fit steady shear data well. Dynamic shear measurements on broth suspensions indicated “gel-like” behavior at low strains, with microstructural breakdown at larger displacements. Time variations of the Casson model parameters (yield stress and Casson viscosity) and dynamic moduli (elastic and viscous modulus) followed both cell mass and morphology: a single maximum in all rheological variables resulted when cells were grown on xylose or on cellulose at impeller speeds of 400 or 550 rpm, and dual maxima were observed for cellulose-grown cells at 250 rpm.     

Rheology of synovial fluid

After a discussion of the role of synovial fluid as a joint lubricant, rheological measurements are described with both normal (healthy) synovial fluids and pathological ones. Shear stress and first normal stress difference are measured as a function of shear gradient to calculate the apparent shear viscosity eta 1 and the apparent normal viscosity psi 7 as well as an apparent shear modulus G'. It is found, that in case of diseased synoviae all rheological parameters deteriorate. Most significant changes are observed with the zero shear viscosity eta 0, the shear modulus G', and a characteristic time theta 1, which is the reciprocal of the critical shear rate Dc which determines the onset of shear thinning. The rheological deterioration of synovial fluids is explained in terms of solute structure, whereby a molecular mass of the backbone hyaluronic acid of at least 10(7) g.mol-1 is required for satisfactory function. A theory of the rheological performance of normal synovial fluid as well as its pathological deterioration is proposed.     

STUDIES ON THE FORMATION AND IONIZATION OF THE COMPOUNDS OF CASEIN WITH ALKALI : I. THE TRANSPORT NUMBERS OF ALKALI CASEINATE SOLUTIONS.

1. The deposition of casein on a platinum anode which takes place on the passage of a direct current through solutions of alkali caseinates was quantitatively studied, and it was found that: (a) the amount of casein which is deposited is directly proportional to the current, i.e. it obeys Faraday''s law; (b) the amount of casein deposited is inversely proportional (within the limits studied) to the amount of alkali which is combined with the casein. 2. A method of determining the transport numbers of proteins insoluble at their isoelectric point has been developed. 3. A titration method for determining the amount of alkali in a casein solution is given. 4. Data from the results of transference experiments on sodium caseinate, potassium caseinate, cesium caseinate, and rubidium caseinate solutions are given. It is shown that the data are best explained on the assumption that in these solutions the carriers of the current are alkali metal cations and casein anions. 5. On the basis of our transference results an explanation is given of the results which were obtained by Robertson and by Haas in their migration experiments.     

Accessibility of Transglutaminase to Induce Protein Crosslinking in Gelled Food Matrices - Impact of Membrane Structure

Enzymes can be used as crosslinking agents to modify the physicochemical properties of food dispersions. However, little is known about the influence of complex interfacial structures on the enzymatic crosslinking rate, particularly in gelled network systems. In the current study, emulsions stabilized by different interfacial membranes (single protein vs. complex coacervates) were incorporated into a hydrogel matrix and then mixed with microbial transglutaminase (mTG) to assess the crosslinking capability. Emulsions stabilized by solely caseinate or coacervates composed of caseinate and beet pectin were fabricated by high shear blending and subsequently embedded into alginate beads. Various alginate (0.5–1.5 %) and CaCl₂ levels (50–500 mM) were used to modulate the hydrogel pore size and number of junction zones. Bradford assay revealed that mTG diffused into the beads, whereas ammonia (NH₃) measurements showed a decrease in NH₃ concentration with increasing alginate and CaCl₂ levels. Theoretical considerations demonstrated that the enzyme-promoted crosslinking is mainly influenced by both the pore size and the number of crosslinks within the network, whereas the interfacial structure had a minor impact on its substrate accessibility.     

Effect of succinylation on the rheological profile of starch pastes

Rheological properties of native corn and amaranth starches, and the changes therein on succinylation have been evaluated. The degree of substitution (DS) was varied from 0.05 to 0.20 at concentrations up to 5%. A strong shear thinning behavior was observed in all the starch pastes, as described by the power law parameters, i.e. the consistency index, K, and the flow behavior or power law index, n. The effect of concentration and DS on the apparent viscosity is described. Amaranth starch succinates showed a greater shear thinning behavior vis-à-vis corn starch succinates. The bulky hydrophilic succinate group seem to influence the rheological properties.     

The invasive brown seaweed Sargassum muticum as new resource for alginate in Morocco: Spectroscopic and rheological characterization

The Japanese brown seaweed Sargassum muticum, recently invaded several shorelines worldwide including the Atlantic coast of Morocco with large well‐established populations. Within the framework of a sustainable strategy to control this invasive seaweed, we report on extraction yield, spectroscopic characterization and rheological properties of alginate, a commercially valuable colloid, from harvested biomass of S. muticum. Extraction yield was about 25.6% on dry weight basis. Infrared spectroscopy analysis shows that the obtained Fourier transform infrared spectra of the extracted biopolymer exhibit strong similarities with that of the commercial alginate. Furthermore, Proton nuclear magnetic resonance spectroscopy revealed that S. muticum alginate has almost equal amounts of β‐D‐mannuronic acid (M; 49%) and α‐L‐guluronic acid (G; 51%) with an M/G ratio of 1.04 and a high content of heteropolymeric MG GM diads suggesting a sequence distribution of an alternated polymer type. Rheological measurements were performed at different sodium alginate concentrations, temperatures and shear rates. The hydrocolloid exhibited pseudoplastic behavior and showed shear thinning, particularly at high solution concentration and low temperature which is consistent with the rheological behavior reported for commercial alginates. Considering the abundance of S. muticum in the Northwestern Atlantic coast of Morocco and the quality of the extracted hydrogel, this invasive species could be considered as a potential source of alginates.