Nonlinear Viscoelastic Region Research Articles

The effect of starch types on extensional, linear and nonlinear rheological properties of starch cracker dough.

Cracker is a popular snack, and their quality depends on the rheological properties of the dough during production. This study focused on the impact of different starch types (tapioca, corn, and potato) used in the same amount (30g) on the rheology of starch cracker dough. Various rheological tests were conducted to assess the dough's properties. Linear viscoelastic properties were determined using oscillatory frequency and temperature sweep tests, while the nonlinear viscoelastic behavior was characterized through stress relaxation and creep recovery tests. Extensional rheological behavior was also examined. Additionally, the textural and thermal properties of the dough were monitored to understand starch gelatinization and its interactions with other components. In the linear viscoelastic region, no significant differences were found between different dough formulations. However, in the nonlinear viscoelastic region, the potato starch-containing formulation exhibited different viscoelastic and textural properties. Biaxial extensional rheological behaviors showed no significant variations between formulations. The temperature sweep test data from differential scanning calorimetry measurements were consistent with temperature sweep data. In summary, this study provides valuable insights into how different starches influence the rheological behavior of starch cracker dough, considering various degrees of deformation and temperature. These findings have implications for cracker production parameters.

Acid-induced gels from mixtures of micellar casein and pea protein: Effect of protein ratio and preheating route

Enhancing the sustainability of dairy products through the partial substitution of dairy proteins with plant proteins requires exploring formulation and processing strategies. This study investigates the gluconic-δ-lactone (GDL)-induced hybrid gels from commercial micellar casein isolate (M) and pea protein isolate (P) dispersions (5% w/w protein content). Variations in the M/P ratios (3:1, 2:2, and 1:3) and preheating routes (Route 1: preheating M and P dispersions together; Route 2: preheating them separately) impacted the physical/conformational properties of protein dispersions as well as the rheological/structural features of resulting gels. Small and large amplitude oscillatory shear (SAOS and LAOS) tests revealed that lower M/P ratio led to earlier gelling points and increased the stiffness and elasticity of hybrid gels in the linear viscoelastic (LVE) region. All gels transitioned from elastic to plastic behavior in the non-linear viscoelastic (NLVE) region, with lower M/P ratio showing reduced stretchability and faster structural breakdown. Regardless of routes, the preheating step (95 °C, 30 min) disintegrated inherent aggregates/agglomerates in these commercial protein ingredients, leading to smaller particle size, but higher protein solubility, surface hydrophobicity, and |ζ-potential|. Pea proteins formed soluble aggregates during preheating, but the presence of micellar caseins (Route 1) hindered this process. Consequently, mixtures with lower M/P ratio and from preheating route 2, possessed higher quantities of pea protein soluble aggregates, forming a compact gel network with low water mobility, as observed by CLSM, STED, and LF-NMR. These findings show the potential for using pea proteins in acid-induced gel foods like yogurt and paneer-type cheeses.

Mechanism and Development of Thermo-Rheological Properties of Asphalts Modified by Reactive Polymer Systems.

The new class of reactive polymers is designed to modify asphalt through chemical reactions with asphalt components. The complexity of such systems and the long experience with thermoplastic elastomers as well as with some other "classical" modifiers, and to a degree that our present testing methods and even specifications revolve around these materials, might obscure the fact that we are dealing with rather different modification systems and possibly with new emerging asphalt paving technologies. Our present work attempted to compare two different reactive polymer systems with the "classical" system which uses thermoplastic elastomer. The impact of reactive polymer systems on asphalt was studied through material properties manifested by specification tests and through the development of thermo-rheological properties in linear and non-linear viscoelastic regions. As expected, the behavior of reactive polymeric systems with different chemistries also differed among themselves. The available results showed that the reactive groups of polymers react with polar components of asphalt leading to higher stiffness at elevated pavement temperatures and differing impact on low temperature properties. The data point to a significantly improved resistance to plastic deformation of pavement in the case of reactive polymers, despite the fact that elastic recovery-based specification tests failed to identify this improvement.

Wheat Flour Quality Assessment by Fundamental Non-Linear Rheological Methods: A Critical Review.

Wheat quality assessment involves physical, physicochemical, chemical, and sensory characterization of wheat kernels and the resulting wheat flour, dough, and bread. The physical tests conducted on wheat flour dough are mostly based on empirical methods. Empirical methods have been useful in industry and research to relate wheat flour quality to baking performance. However, these methods have the disadvantage of providing data in arbitrary units, which makes the fundamental interpretation of results difficult. Therefore, this review focuses on the use of fundamental rheological methods to determine wheat flour quality in terms of processing performance. During the transition from wheat flour to bread, wheat flour dough is mostly exposed to large deformations, and the quality of wheat flour determines its response to these large deformations and its baking quality. For this reason, this review only focuses on the application of fundamental rheological tests that are conducted in the non-linear viscoelastic region where wheat flour dough experiences large deformations.

Stiffening and Toughening of Asphalt Mastic Induced by Bitumen–Mineral Selective Molecular Adsorption and Nanostructural Reconstruction

Asphalt mastic is the most important binder in asphalt mixtures and its rheology is inevitably influenced by the mineral aggregates. Due to the little consideration that has been paid to aggregates’ effects, the rheological properties of mastic films have not been accurately characterized for the present method. Therefore, this study aimed to investigate the rheological characteristics of mastic affected by mineral aggregates and reveal its fundamental mechanism of interfacial interaction. The results suggest that the aggregates increased the stiffness and toughness of mastic within the linear and nonlinear viscoelastic regions. The mastic on limestone had a higher linear viscoelastic modulus than that on basalt below 35 °C, and its ratio reached up to 1.18. However, the modulus of the mastic on basalt surpassed that on limestone by over 50 °C, and the maximum ratio reached 2.17. The mastic in contact with the limestone had a higher failure strain and failure modulus than that in contact with the basalt, the ratios of which reached 1.60 and 1.32, respectively. The macrorheological characteristics are closely related to the nanostructures and intermolecular interactions of bitumen–mineral systems. The coexistence of a stable bitumen nanostructure and an adsorbed layer on the calcite substrate provided a strong bonding energy and high resistance to external shear deformation, leading to the high stiffness and toughness of the limestone. Abundant metal ions from augite and albite diffused into the bitumen layer and destroyed its nanostructure, decreasing the stability of the mastic–basalt interface system. The non-bond energy of bitumen-calcite was 14.15% higher than that of bitumen-albite, and the ratio of shear stress of the bitumen-calcite to the bitumen-albite reached up to 6.8. Therefore, the calcite in limestone reinforced the bitumen, and the augite and albite in basalt destroyed the bitumen colloidal structure. This provides a fundamental understanding of the rheological characterization of mastic on mineral aggregates.

Nonlinear viscoelastic behavior and their time-temperature superposition for filled styrene butadiene rubber compounds and vulcanizates

The nonlinear viscoelastic behavior of rubber composites is of great practical importance in their processing as well as the application. In this paper, nonlinear viscoelastic behavior for vulcanized and unvulcanized filled styrene butadiene rubbers (SBR), SBR/carbon black (CB) composites, were mainly investigated. Besides the conventional Payne effect, frequency (ω) sweep tests at different strains (linear and nonlinear viscoelastic regions) were performed to get more information about viscoelastic response, especially in nonlinear region that close to actual driving conditions. Conductivity synchronization test was also operated to explore the evolution of CB agglomerates. It reveals that the filler network structure recovers slowly but the rubber network recovers rapidly during an increasing and decreasing strain sweep cycle. At large strain, rheological parameters of vulcanizates change significantly with increasing ω. A pseudomaster curve based on the ω sweep at large strain and different temperature can be obtained both for compounds and vulcanizates, indicating that the time-temperature superposition is also applicable to the nonlinear viscoelastic behavior. Similar linear and nonlinear viscoelastic behaviors of filled vulcanizates to that of unfilled vulcanizates demonstrate the same mechanism of viscoelastic response. The loss modulus peak of filled vulcanizates primarily comes from the Rouse movement of rubber chains between crosslinking points. Under large strain, the strain amplication effect of particles hardly influence the characteristic relaxation time of Rouse movement between crosslinking points.

Low heat generation from organic zinc as a curing activator in rubber and rubber composites under large strain

AbstractZnO is a conventional activator in sulfur curing systems, but its excessive release can cause adverse effects to the human body and the environment. Using organic zinc instead of zinc oxide not only decreases the amount of zinc but also disperses the zinc into the natural rubber (NR) matrix more effectively. The results showed that the six organic zinc compounds accelerated the curing process and weakened the Payne effect compared to those with ZnO. Dynamic frequency scan tests of the vulcanizates in linear (small strain) and nonlinear (large strain) viscoelastic regions were performed. Different from that at small strain, there was a great change in the storage modulus, loss modulus and loss factor at large strain. For unfilled NR, the systems with zinc oleate, zinc 2‐ethylhexanoate and zinc acetate as activators showed a weaker Payne effect and low heat generation because of the homogeneous dispersion. For NR/CB (carbon black) composites, the systems with zinc acetate, zinc o‐glycerol and zinc 2‐ethylhexanoate showed a weaker Payne effect and low heat generation at large strain and high frequency due to the homogeneous dispersion and the strong interaction with CB particles. These results will help to clarify the advantages of organic zinc instead of zinc oxide in reducing heat generation for rubber products.

Modified Bouc-Wen Model Based on Fractional Derivative and Application in Magnetorheological Elastomer

To accurately characterize the mechanical behavior of magnetorheological elastomer (MRE) under a wide range of strain amplitude, excitation frequency, and magnetic field, the viscoelastic fractional derivative was introduced, and a modified Bouc-Wen model based on fractional derivative for MRE in a nonlinear viscoelastic region was established. The Bouc-Wen model can accurately describe the hysteretic characteristics of the MRE nonlinear viscoelastic region, but it cannot accurately simulate magneto-viscoelasticity and frequency dependence. The fractional derivative can express this characteristic with fewer parameters and higher accuracy. The model’s validity was verified by fitting the experimental data of stress and strain measured in shear mode. By analyzing the coupling relationship between the model parameters and strain amplitude, frequency, and magnetic flux densities, a method of parameter identification under multi-loading conditions was proposed, and the modified model parameters were identified. The results reveal that the modified Bouc-Wen model can accurately characterize the mechanical properties of the nonlinear viscoelastic region of MRE, and the fitting accuracy is significantly improved compared with the Bouc-Wen model. The expression of the model parameters obtained from the method of parameter identification under multi-loading conditions is accurate in a wide range of strain amplitude, frequency, and magnetic flux density. The fitness values of simulation data and experimental data under identified and non-identified conditions exceed 90%, showcasing the effectiveness of the modified Bouc-Wen model and the feasibility of the parameter identification method under multi-loading conditions.

Nonlinear oscillatory shear tests of pressure-sensitive adhesives (PSAs) designed for transdermal therapeutic systems (TTS)

Transdermal therapeutic systems (TTS) based on pressure-sensitive adhesives (PSAs) allow for the application of pharmaceutical substances via diffusion through the skin. The rheological performance of PSA is largely investigated within small amplitude oscillatory shear (typically up to 1 %), although the skin motions exceed strains beyond 40 %. In this paper, amine-compatible (AC) and non-amine-compatible (NAC) silicone-based PSA compounds differing in the resin content were subjected to strain amplitude sweeps in a twin drive rheometer. Carreau-Yasuda-like fitting of storage and loss moduli curves intercepts the substantial effect of resin content on both compounds; up to four times higher, moduli of AC compounds were determined in SAOS, and their higher molecular mass combined with enhanced interactions contributed to an earlier transition to the nonlinear viscoelastic region. In the nonlinear range, elastic and viscous properties are affected by strains in a different manner with the trend favorable for the PSA application as TTS. The third relative higher harmonic from Fourier transformation I3/1 as well as intra-cycle strain stiffening and shear thickening ratios provide information relevant for an optimization of PSA subjected to large deformations.

Effects of hydrocolloids, acids and nutrients on gelatin network in gummies

Gelatin is a commonly used gelling agent in many confectionery gel (CG) products such as gummy candies. The rheological behaviors of gelatin in gummy products are still poorly understood. The objective of this study was to investigate how gummy formulation affects rheological behaviors of the gelatin network in both linear and nonlinear viscoelastic regions. The effects of °Brix, acids, hydrocolloids, and nutrients on gelatin gelation in gummies were investigated using both small amplitude oscillatory shear (SAOS) tests and large amplitude oscillatory shear (LAOS) tests. °Brix appeared not to impact the gelling temperature of the gelatin gummy until it reached 80 or higher when the gelling temperature decreased probably due to the extrusion of sugar from the gelatin network. Both citric acid and malic acid weakened the gelatin gummy network due to their restrictive effect on the formation of hydrogen bonds. Incorporating hydrocolloids, such as pectin and agar-agar, into the gelatin gummy showed synergistic effect on the gel network due to the nature of hydrocolloids and the ratio to gelatin in the formulation. Incorporating inulin into gelatin gummy enhanced the gel network through hydrogen bonding between inulin and gelatin. As indicated by the frequency sweep tests, incorporating whey protein isolate caused a whey protein dominated bi-continuous gel network which was enhanced by the presence of gelatin. Large deformation rheological tests showed that the gelatin gummy with 81 °Brix had greater nonlinear behaviors under large shear strains, whereas gelatin gummy with 78 °Brix was more resistant to the large deformation. These gelation and stability differences of gelatin gummy network can contribute to the differences in texture and stability of gummies during processing and storage.

Special Features of Nonlinear Behavior of a Polymer Solution on Large Periodic Deformations

Study of the behavior of polymer solution flows in the region of nonlinear viscoelasticity allows one to more accurately evaluate the adequacy of rheological models and to describe the rheological properties of a material in more detail. The nonlinear viscoelastic properties manifesting themselves in the process of studying the behavior of a polymer material on significant deformations were investigated with the aid of time dependences of shear stresses calculated at different amplitudes. The present work considers the applicability of the modified Vinogradov–Pokrovskii rheological model to describing the oscillating shearing of polymer fluids with a large amplitude. It has been established that on increase of the deformation amplitude, the shear stresses cease to be a true harmonic, and one observes the appearance of a "step" on their left front, which speaks of the substantial nonlinearity in the behavior of the sample. The obtained theoretical dependences are compared with experimental data for a 5% solution of polyethylene oxide in dimethyl sulfoxide. The comparison was made as by plotting the time dependences of normalized stresses, so by analyzing Lissajous figures. Despite the simplicity, the modifi ed Vinogradov–Pokrovskii rheological model adequately describes the behavior of polymer materials on significant periodic deformations.

Nonlinear rheological behaviors of epoxy asphalt binder compared to base asphalt binder and SBS modified asphalt binder at above ambient temperatures

When heavy vehicles load at high temperatures, the mechanical responses of asphalt binders are probable in the nonlinear viscoelastic regions. However, the nonlinear viscoelasticity of asphalts at above ambient temperatures is seldom studied. In this paper, large amplitude oscillatory shear was used to characterize the nonlinear rheological behaviors of three typical asphalt binders including base asphalt (BA), thermoplastic styrene–butadiene–styrene modified asphalt (SBA) and thermosetting epoxy asphalt (EA) at temperatures of 25, 45, 65, 85, 100 °C, respectively. The inter-cycle yielding behaviors of BA, SBA and EA were observed by strain sweep tests at relatively low temperatures. And the strong intra-cycle yielding and intra-cycle stiffening behaviors were detected for EA at 25 °C, while slight intra-cycle yielding behaviors were observed for BA and SBA through the shape of Lissajous curves. With temperature increasing, nonlinear responses of the three asphalt binders gradually disappear at different rates, which were validated by strain stiffening index S. To some extent, the strain and temperature dependence of nonlinear behaviors displayed in Lissajous curves can be manifested in strain sweep tests. The dissipation ratio φ indicates that with the increase of temperature BA and SBA gradually transform from viscoelastic solids eventually to Newtonian fluids at 100 °C, while EA nearly behaves purely elastic at 100 °C originated from the crosslinking networks. These results could be responsible for the differences of nonlinear characteristics and practical performances among the three kinds of binders.

Application of graphene oxide nanosheets and HPAM aqueous dispersion for improving heavy oil recovery: Effect of localized functionalization

Using efficient methods to recover heavy oil is crucial for economic success. Polymer flooding is a very efficient way to sweep oil reservoirs at both macroscopic and microscopic scales by increasing the viscosity of injected water. Recently, it was shown that addition of nanomaterials to polymer solutions may improve the flooding performance and recovery. In this work, two different types of graphene oxide (GO) nanofillers with different different location of OH group functionalization (functionalization mainly on basal plane (S-GO) and functionalization mainly on the edges (E-GO)) were synthesized to improve the rheological behavior and oil recovery efficiency of a partially hydrolyzed polyacrylamide (HPAM) solutions. To characterize the chemical structure of both GOs, thermogravimetric analysis (TGA) and Raman spectroscopy were employed. Frequency sweep, creep, creep recovery, shear start-up, and strain sweep tests were also utilized to evaluate the viscoelastic behavior of HPAM solutions, with or without the nanofillers in both linear and nonlinear viscoelastic regions. Cryo-SEM images of the hybrid dispersion of HPAM/GOs were captured to assess the dispersion state of all systems. A core flooding set up was used to evaluate the effectiveness of all dispersions in improving the viscous oil recovery by polymer injection. Rheological properties showed that addition of 0.2 wt% of both GOs reduced dynamic moduli. However, due to the better dispersion of S-GO in a HPAM solution, incorporation of 0.2 wt% of S-GO to the HPAM solution, improved the oil recovery by 7.8% compared to the HPAM solution.

Effect of Carbon Nano Tube on performance of asphalt binder under creep-recovery and sustained loading conditions

Abstract The present study aimed at evaluating the rutting performance of Carbon Nano Tube (CNT) modified asphalt binder under different loading conditions. CNT content was varied as 0%, 0.4%, 0.75%, 1.5% and 2.25% by the weight of control binder. Superpave rutting parameter (G*/Sinδ) and Shenoy parameter (G*/(1-(1/TanδSinδ))) were initially evaluated using temperature sweep test. Though both parameters showed a similar trend, the later one found to have more sensitivity towards evaluating unrecoverable strain value. Creep-recovery test was further conducted at four different stress levels (100 Pa, 3200 Pa, 5000 Pa, and 10000 Pa) to understand the effect of CNT under cyclic loading-unloading condition. Improvement in recovery value and a corresponding decrease in non-recoverable creep compliance value was observed with the addition of CNT. Further attempt was made to model the strain response from creep-recovery test using the Burgers model and Power model. Based upon the variation of viscous component of steady flow obtained from the Burgers model, CNT addition found to improve the rutting performance. Further, the power model also showed an excellent prediction of strain response under creep period, however, deviation from the experimentally observed response was observed in the recovery period. Modification to the power law model was done which significantly improved the strain prediction in the recovery period. Likewise, the effects of CNT under sustained loading condition was evaluated using a creep test at two different stress levels (100 Pa and 3200 Pa). Incremental dosages of CNT shifted the binder response from linear to nonlinear viscoelastic region at comparatively lower creep period. Significant decrease in deformation rate was also observed with CNT addition.

Nonlinearity in the Mechanical Response of Rubber as Investigated by High-Frequency DMA.

Nonlinear material response is analysed with the Fourier transform (FT) of the raw signal measured by a high-frequency dynamic mechanical analyzer (HF DMA). It is known from rheological behaviour of elastomers that reinforcing fillers additionally induce nonlinearity in an already inherently nonlinear system. This behaviour is often described in terms of a mechanical response of strain sweeps, essentially the transition from the linear viscoelastic (LVE) to the nonlinear viscoelastic (NVE) region. In the current investigation, the NVE region could be observed with respect to frequency under low-amplitude deformation. A foldover effect was observed, whereby the material exhibited a nonlinear dependency in relation to the increment of the filler amount above the percolation threshold. In addition, an apparent superharmonic resonance was observed within higher orders of vibrational modes which is further indication of nonlinearity. In this paper, the analytical approach is presented as a novel method to characterise the behaviour of the polymer–filler interaction by HF DMA.

Rheological design of 3D printable all-inorganic inks using BiSbTe-based thermoelectric materials

In order to achieve high-quality 3D printing of inorganic materials, a thorough evaluation of appropriate rheological characteristics and methodologies for formulating all-inorganic inks is required. We recently reported all-inorganic inks using BiSbTe-based thermoelectric particles coupled with a chalcogenidometallate (ChaM) inorganic binder. In the current study, we analyzed the rheological behavior of the all-inorganic inks to assess printability and 3D structural retention with respect to the ChaM content. The stress sweep and three-interval thixotropy test (3ITT) were conducted to mimic a 3D printing and interpret the flow behavior under nonlinear viscoelastic region. The binder-free inks showed a sharp overshoot of the loss modulus (G″) followed by the fluctuation of both the storage modulus G′ and G″ in the stress range of 10–50 Pa. In addition, the inks developed stronger colloidal structure than the initial state after the 3ITT, resulting in the non-uniform jetting. The nonlinear flow of the inks became stable by incorporating ChaM. However, the excessive ChaM (37.5 wt. %) brought about stress-induced structure regeneration analogous to the binder-free inks. The 3D structure integrity was interpreted by yield stress and solid-like characteristics based on the frequency sweep results after undergoing deformation. Poor printability from the 12.5 wt. % ChaM-containing ink was correlated to low yield stress (2 Pa) and a high slope of the G′ curve. However, the 25 wt. % ChaM-containing ink gave a high yield stress of 48 Pa and a low G′ curve slope of 0.2 even after nonlinear deformation, resulting in high 3D shape retention and printability.In order to achieve high-quality 3D printing of inorganic materials, a thorough evaluation of appropriate rheological characteristics and methodologies for formulating all-inorganic inks is required. We recently reported all-inorganic inks using BiSbTe-based thermoelectric particles coupled with a chalcogenidometallate (ChaM) inorganic binder. In the current study, we analyzed the rheological behavior of the all-inorganic inks to assess printability and 3D structural retention with respect to the ChaM content. The stress sweep and three-interval thixotropy test (3ITT) were conducted to mimic a 3D printing and interpret the flow behavior under nonlinear viscoelastic region. The binder-free inks showed a sharp overshoot of the loss modulus (G″) followed by the fluctuation of both the storage modulus G′ and G″ in the stress range of 10–50 Pa. In addition, the inks developed stronger colloidal structure than the initial state after the 3ITT, resulting in the non-uniform jetting. The nonlinear flow of the inks...

Study on the creep and recovery behaviors of ferrofluids

The creep and recovery behaviors of lubrication oil based ferrofluids of different particle concentration were systematically investigated to understand the viscoelasticity of ferrofluids. The influence of stress level, magnetic field strength and temperature on creep and recovery behaviors of ferrofliuids was studied experimentally and the microscopic mechanisms behind the rheological phenomenon were discussed. Linear viscoelasticity theory and generalized Burgers models were employed to analyze the experimental results. The experimental results demonstrate that the ferrofluids exhibits unique creep and recovery properties significantly different from other stimuli responsive materials both in the linear and nonlinear viscoelastic region. Furthermore, structures larger than single chains are supposed to be responsible for many experimental results, including the extended relaxation process in recovery phase and the nonlinear increasing trend of creep strain with magnetic field strength and temperature. These findings contribute to a better understanding of the microscopic mechanism of magnetorheology of ferrofluids and also provide guidance for many practical applications.

A correlation between microstructure and rheological properties of broad MWD high-density polyethylene

A correlation between molecular structure parameters and rheological behavior was determined for three different grades of high-density polyethylene (HDPE). The molecular structure parameters including number-average molecular weight (M n ), weight-average molecular weight (M w ), molecular weight distribution (MWD) and branching index were characterized by gel permeation chromatography (GPC). Moreover, a fast and easy method for investigating side chain branching using Fourier transform infrared (FTIR) spectroscopy was discussed. The rheological characterizations of both linear and non-linear viscoelastic regions were performed by a modular compact rheometer (MCR) in the dynamic mode. Zero shear viscosity (η 0), relaxation time, relaxation time distribution, stress relaxation modulus and damping function were obtained from the rheological characterization. Moreover, molecular weight distribution was calculated for each sample and compared with the GPC results. The GPC results confirmed broad molecular weight distribution for all three HDPE samples. The relationship between zero shear viscosity and molecular weight at 180 °C was found as \(\eta_{0} = 2.5 \times 10^{ - 14} M_{w}^{3.6}\) and for zero shear viscosity and MWD at 180 °C was found as \(\eta_{0} = 1.6 \times 10^{ - 15} M_{w}^{3.6} \left( {\frac{{M_{w} }}{{M_{n} }}} \right)\). By choosing the mixing parameter (β) value of 0.73, the values of molecular parameters obtained from the rheology and GPC tests were significantly accommodated. Furthermore, it was found that the damping function of type C was an appropriate type for the polyethylenes of selected broad MWD.

Effect of lime concentration on gelatinized maize starch dispersions properties

Maize starch was lime-cooked at 92°C with 0.0–0.40% w/w Ca(OH)2. Optical micrographs showed that lime disrupted the integrity of insoluble remnants (ghosts) and increased the degree of syneresis of the gelatinized starch dispersions (GSD). The particle size distribution was monomodal, shifting to smaller sizes and narrower distributions with increasing lime concentration. X-ray patterns and FTIR spectra showed that crystallinity decreased to a minimum at lime concentration of 0.20% w/w. Lime-treated GSD exhibited thixotropic and viscoelastic behaviour. In the linear viscoelastic region the storage modulus was higher than the loss modulus, but a crossover between these moduli occurred in the non-linear viscoelastic region. The viscoelastic properties decreased with increased lime concentration. The electrochemical properties suggested that the amylopectin-rich remnants and the released amylose contained in the continuous matrix was firstly attacked by calcium ions at low lime levels (<0.20% w/w), disrupting the starch gel microstructure.

Effect of inulin and agave fructans addition on the rheological, microstructural and sensory properties of reduced-fat stirred yogurt

The effect of medium chain inulin (IN) and agave fructans (FR) at concentrations of 20, 40, and 60 g L−1 on the microstructural, rheological and sensory properties of reduced milk-fat (RIN or RFR, 13 g of milk fat L−1) stirred yogurts were investigated in comparison with those of a full-fat control (FC, 26 g of milk fat L−1) yogurt. Scanning electron micrographs revealed that RIN and RFR showed different protein network arrangements than FC. FR tended to cover the casein micelles, while IN formed secondary gelled structures. RIN40 and RFR60 exhibited sensory characteristics (viscosity, creaminess, flavour and overall acceptability) that were deemed superior than those of FC. The loss tangent values in the linear and the stress values corresponding to the crossover point between the storage and loss moduli in the non-linear viscoelastic regions provided indicators that closely agreed with sensory evaluation perceptions.