Rheological Research Articles

Role of the pea protein aggregation state on their interfacial properties

HypothesisPlant protein ingredients from similar sources can vary in functionality not only because of compositional differences, but also because of differences in their structure depending on their processing history. It is essential to understand these distinctions to develop novel food emulsion using plant proteins. It is hypothesized that differing interfacial properties can be attributed to their structures, aggregation, and colloidal states. ExperimentsThe adsorption behavior of a commercial protein isolate, homogenized or non-homogenized, was compared to a mildly extracted isolate to evaluate the effect of aggregation state and structural differences. After characterization of the particle size and protein composition, the interfacial properties were compared. FindingsAtomic force microscopy provided evidence of interfaces packed with protein oligomers regardless of the treatment. Differences in adsorption kinetics and interfacial shear rheology depending on oil polarity suggested different interfacial structures. A polydisperse mixture of protein oligomers resulted in increased rearrangements and protein-protein interactions at the interface. Homogenization of commercial proteins resulted in a lower interfacial tension and less elastic interfaces compared to those of native proteins due to the presence of larger aggregates. This study highlights how the interfacial properties can be related to the protein aggregation state resulting from differences in processing history.

Temperature oscillations provide access to high-order physical aging harmonics of a glass forming melt

A high-resolution, temperature oscillation-based probe of physical aging in complex systems is introduced. The Fourier analysis of the measured responses allows one to extract high-order, aging-related nonlinearities that are not accessible via traditional temperature-jump and temperature-ramp procedures. To demonstrate the potential of this oscillatory approach, we analyze the periodic time evolution of glycerol’s structural relaxation using shear rheology as a vehicle. Thereby, we access up to the sixth harmonic and detect aging fingerprints within a resolution range of three orders of magnitude for temperature amplitudes of up to 4 K. The even harmonics are present since aging is not symmetrical with respect to the direction of temperature change. The high-order aging coefficients obtained for glycerol are described reasonably well within the Tool–Narayanaswamy–Moynihan formalism.

Rethinking the relationships between gel like structure and sludge dewaterability based on a binary gel like structure model: Implications for the online sensing of dewaterability

The digital transformation of sludge treatment processes requires online sensing of dewaterability. This topic has been attempted for many years based on macroscopic shear rheology. However, the relationship between rheological behavior and dewaterability remains noncommittal, and the reason is unclear. Herein, a binary gel-like structure model was proposed including the interactions network at the supra-flocs level and the gel-like structure at the flocs level. Multiple advanced techniques including optical tweezers were employed to precisely understand the binary gel-like structure and to classify the correlation mechanism between this gel-like structure, rheological behavior, and dewaterability. The analysis of sludge from eight wastewater treatment plants showed the binary gel-like structures at both supra-flocs and flocs levels have significant relationships with sludge dewaterability (p < 0.05). Further deconstruction of the sludge viscoelastic behavior illustrated that the gel-like structure at the supra-flocs level dominates the rheological behavior of sludge. Moreover, the direct description of the binary gel-like structure in four typical sludge treatment processes highlighted the importance of the flocs level's structure in determining the dewaterability. Overall, this study revealed that shear rheology may prefer to stress the interactions network at the supra-flocs level but mask the flocs level's structure, although the latter is important. This observation may provide a general guideline for the design of robust sensors for dewaterability.

Evaluation of the rheological properties and aging resistance of asphalt modified by MDI/TDI polyurethane

The high cost and high dosage of polyurethane (PU) used in asphalt modification limit its application in asphalt pavement construction. To address these problems, two novel PUs were synthesized by the reaction of low-cost polypropylene glycol (PPG-2000) separately with 4,4 - diphenylmethane diisocyanate (MDI) and with toluene diisocyanate (TDI). This study has further optimized the preparation process and analyzed the influence of the PU synthesis materials on the modified asphalt. Dynamic shear rheology, multiple-stress creep recovery, Fourier-transform infrared spectroscopy, and fluorescence microscopy were used to evaluate the rheological properties and aging resistance of modified asphalt. Results show that the PUs synthesized by MDI and TDI significantly improved the high-temperature performance, low-temperature performance, and aging resistance of modified asphalt compared to unmodified asphalt. Asphalt modified with the PU synthesized by MDI had better high-temperature performance, but the low-temperature performance and aging resistance were worse than those for asphalt modified with the PU synthesized by TDI. The results of rheological aging and chemical aging evaluation showed that the PU synthesized by TDI provided better anti-aging performance. The optimum dosages of both PUs were not more than 6%. These PUs reduce the cost of construction engineering and show excellent application prospects in pavement construction. These two PU-modified asphalts can be applied to pavement construction in different regions based on the properties required.

Benchmarking of a microgel-reinforced hydrogel-based aqueous lubricant against commercial saliva substitutes

Xerostomia, the subjective sensation of ‘dry mouth’ affecting at least 1 in 10 adults, predominantly elders, increases life-threatening infections, adversely impacting nutritional status and quality of life. A patented, microgel-reinforced hydrogel-based aqueous lubricant, prepared using either dairy or plant-based proteins, has been demonstrated to offer substantially enhanced lubricity comparable to real human saliva in in vitro experiments. Herein, we present the benchmarking of in vitro lubrication performance of this aqueous lubricant, both in its dairy and vegan formulation against a range of widely available and employed commercial saliva substitutes, latter classified based on their shear rheology into “liquids”, “viscous liquids” and “gels”, and also had varying extensional properties. Strikingly, the fabricated dairy-based aqueous lubricant offers up to 41–99% more effective boundary lubrication against liquids and viscous liquids, irrespective of topography of the tested dry mouth-mimicking tribological surfaces. Such high lubricity of the fabricated lubricants might be attributed to their limited real-time desorption (7%) from a dry-mouth mimicking hydrophobic surface unlike the tested commercial products including gels (23–58% desorption). This comprehensive benchmarking study therefore paves the way for employing these microgel-based aqueous lubricant formulations as a novel topical platform for dry mouth therapy.

Application of the Air-Jet Laser Detection Technology for Asphalt Binders

AbstractA fast and convenient technique for Asphalt Binders was proposed in this paper, which was based on air-jet pressurized and laser to detect the transient deformation and creep recovery of asphalt. Taking five kinds of asphalt and modified asphalt commonly used in China as the research objects, the performance of asphalt were tested and analyzed by adopting the Penetration Test, Dynamic Shear Rheological (DSR) Test, Multiple Stress Creep and Recovery (MSCR) Test and the proposed test technology. The results verified the feasibility of the proposed test technology and the correlation between the traditional tests and the proposed test technology. The results demonstrated that the proposed test technology had good discrimination ability for different kinds of asphalt and could effectively reflect the performance differences. The new test protocol was similar to the Penetration Test. There was a significant correlation between the maximum deformation index and penetration index. The correlation coefficient was above 0.8, and the p value was much less than 0.01. It could be used as a possible alternative to the Penetration Test. The proposed new test was relatively convenient and fast compared with the dynamic shear test. There was a linear correlation between the maximum deflection index and the complex shear modulus G*, and the correlation coefficient between the recovery index and the phase angle is above 0.8, which indicated that the proposed new test and the DSR test had a significant correlation. There was also a good correlation between the creep recovery index of MSCR test and the recovery data of the proposed new test method. The research results provided a new solution for the performance test and evaluation of asphalt in China.

Synthesis and Aggregation Behavior of Hexameric Quaternary Ammonium Salt Surfactant Tz-6C12QC.

A hexameric quaternary ammonium salt surfactant Tz-6C12QC featuring a rigid triazine spacer and six ammonium groups was synthesized. The molecular structure and aggregation behavior of Tz-6C12QC were characterized by nuclear magnetic resonance spectroscopy, surface tension, conductivity, dynamic light scattering, and transmission electron microscopy, etc. Dissipative particle dynamics (DPD) simulation was employed to investigate the self-assembly behavior of Tz-6C12QC at different concentrations. The rheological behavior of the polyacrylamide/Tz-6C12QC system was characterized by shear rheology. The results indicated that Tz-6C12QC exhibited superior surface activity and lower surface tension compared to conventional surfactants. Rheology analysis revealed that Tz-6C12QC had a significant viscosity reduction effect on polyacrylamide. DLS and TEM indicated that, as the concentration of Tz-6C12QC increased, monomer associations, spherical aggregations, vesicles, tubular micelles, and bilayer vesicles were sequentially formed in the solution. This study presents a synthetic approach for polysurfactants with a rigid spacer and sheds light on the self-assembly process of micelles.

Effect of fiber properties and orientation on the shear rheology and Poynting effect in meat and meat analogues

The development of plant-based meat analogues is an important aspect of the transition towards using more plant proteins. Production of such products with texture (and rheology) adequate for consumer acceptance like meats is a great challenge. However, there is a current lack in quantitative methods to compare whole cut meats and plant-based analogues that also consider its fibrous structures. We tackled this problem by combining non-linear shear rheology and shear-induced normal stress measurements on whole cut meats (beef and chicken) and plant-based fibrous model systems for meat analogues (soy and pea protein isolates combined with wheat gluten). We found different response in the linear viscoelastic regime for different samples, and the non-linear viscoelastic regime provided a deeper understanding into the role of structural components. Meat samples showed rearrangements at small strains and lower energy dissipation, higher intracycle strain stiffening, and a larger normal stress response at large strains than plant-based fibrous products, due to more elastic fibers. The plant-based fibrous products behave more solid-like until a larger strain, but the fibrous structures break down at large deformations resulting in higher energy dissipation, and show a lower normal stress response than meat. We therefore explore the importance of fiber properties and orientation on the nonlinear rheology of fibrous model systems for meat analogues, and provide a robust methodology to quantitatively compare different mechanical responses of meat and plant-based fibrous meat analogues. These results thereby allow comparison and tuning mechanical responses of plant-based meat analogue products towards real meat.

Influence of Modified Stalk Fibers on the Fatigue Performance of Asphalt Binder

The type and content of modified stalk fibers significantly influence the fatigue properties of asphalt binder. In this study, different concentrations of NaOH solution were used to modify stalk fibers, and scanning electron microscopy (SEM) was used to observe the effect of the modified concentration on the fiber morphology. A dynamic shear rheology (DSR) test and a linear amplitude sweep (LAS) test were conducted to analyze the effects of the fiber type and content on various factors such as the complex shear modulus G*, phase angle δ, and fatigue parameters (A35 and B). Consequently, the fatigue life Nf of the fiber asphalt binder was calculated using a viscoelastic continuum damage model. The results show that stalk fibers modified using a 5% alkali solution exhibited the best oil absorption and heat resistance, the asphalt binder with a 1.5%–2% fiber content exhibited the best resistance to fatigue, and the fatigue performance of the asphalt binder with different types of fibers was superior when fiber doping was at 1.5%. Additionally, the fatigue parameter A35 of the modified cotton and corn stover fibers increased by 40.5% and 57.6%, respectively, and the fatigue parameter B decreased by 5.8% and 4.8%, respectively, compared with that of the unmodified stover fibers. Finally, the modified corn stalk fiber asphalt binder with a 1.5% fiber content demonstrated the best fatigue resistance.

Natural and Engineered Isoforms of the Inflammasome Adaptor ASC Form Noncovalent, pH-Responsive Hydrogels.

The protein ASC polymerizes into intricate filament networks to assemble the inflammasome, a filamentous multiprotein complex that triggers the inflammatory response. ASC carries two Death Domains integrally involved in protein self-association for filament assembly. We have leveraged this behavior to create noncovalent, pH-responsive hydrogels of full-length, folded ASC by carefully controlling the pH as a critical factor in the polymerization process. We show that natural variants of ASC (ASC isoforms) involved in inflammasome regulation also undergo hydrogelation. To further demonstrate this general capability, we engineered proteins inspired by the ASC structure that also form hydrogels. We analyzed the structural network of the natural and engineered protein hydrogels using transmission and scanning electron microscopy and studied their viscoelastic behavior using shear rheology. Our results reveal one of the very few examples of hydrogels created by the self-assembly of globular proteins and domains in their native conformation and show that Death Domains can be used alone or as building blocks to engineer bioinspired hydrogels.

Improving food sustainability by converting orange peel waste products into hydrogels using stirred media milling

There is a need for natural gelling ingredients within the food industry. We have shown that orange peel suspensions (OPS) form hydrogels when treated with a stirred media mill. Gels were formed when an aqueous 3% OPS was milled for longer than 60 min. Their gel strength increased with milling time, which was attributed to progressive disruption of the plant cell tissues and release of pectin and other polysaccharides. The water holding capacity and amount of bound water in the orange peel gels increased with milling time. Shear rheology experiments showed that the gels exhibited shear thinning and were predominantly elastic-like materials. FTIR analysis and addition of bond disruptive agents suggested that hydrophobic interactions between methoxy groups on the pectin were mainly responsible for crosslinking and gelation. Overall, our results suggest that stirred media milling may improve the utilization of orange peel as a functional ingredient in the food industry.

Creation of Next-Generation Plant-Based Seafood Using Emulsion Gel Technology: Omega-3-Enriched Sea Foie Gras Analogs

Plant-based seafood analogs are gaining increasing popularity as replacements for traditional fish and other seafood products due to environmental (stock depletion, pollution, and bycatch issues) and health (bioaccumulated toxins, norovirus, and allergies) concerns associated with them. Several companies have launched plant-based fish products, but the market still lacks alternatives to shellfish and other sea delicacies. In this study, a plant-based sea foie gras (monkfish liver product) analog was developed using duckweed RuBisCO protein and omega-3-rich flaxseed oil to form emulsion gels. These gels consisted of a high concentration of flaxseed oil droplets dispersed within a gelled RuBisCO protein network. It was hypothesized that the high disperse phase volume fraction of the oil droplets and the heat-set gelation properties of the RuBisCO proteins would enable us to create emulsion gels that mimicked the properties of sea foie gras. A natural pigment (β-carotene) was incorporated into the oil phase of the emulsions to mimic the red-orange color of conventional sea foie gras. The structural, textural, and optical properties of real and plant-based sea foie gras analogs were characterized using scanning electron microscopy, confocal microscopy, dynamic shear rheology, texture profile analysis, and colorimetry. Emulsion gels prepared using 40% flaxseed oil and 10% RuBisCO proteins produced plant-based products that closely simulated the texture and color of the real products. Rheological analysis suggested that the oil droplets acted as active fillers within the protein gels. Our results suggest that emulsion gels may be used to create more sustainable and healthier plant-based seafood products.

Small and large deformation rheology on pizza cheese as an example of application to study anisotropic properties of food soft materials

Various rheological techniques were applied to study pizza cheese, as a model anisotropic material. Small Amplitude Oscillatory Shear (SAOS) was combined with Large Amplitude Oscillatory Shear (LAOS) rheology, and the data compared to large deformation tests and confocal microscopy. Pizza cheese was analyzed at various stages of processing: before/during mixing, freshly stretched and after 1 and 2 weeks of storage. Directional sampling and testing were of critical importance for data interpretation. LAOS data were evaluated using a recently developed software that, with visual interactive analysis, including layover plots and similarity maps, allowed to provide a rheological fingerprint of the cheese's process and storage-induced structural changes. This work demonstrated that by using complementary rheological and microstructural techniques it is possible to improve our understanding of the anisotropy at different length scales, and to distinguish the differences in the networks among samples after various processing stages.

Concentration-dependent rheological characteristics of chickpea (Cicer arietinum L.) flour dispersion in steady and dynamic shear

Chickpea (Cicer arietinum L.) flour (CF) is the basic raw material used in the form of dispersion in varied concentrations for making promising oriental sweets and snacks in the Asian subcontinent. The finished product quality of these fried food items thus mainly depends on the consistency of flour dispersions. Therefore, a concentration-dependent steady-state and dynamic rheological study, along with the pasting behaviour, was carried out. Steady shear rheology exhibited concentration-dependent pseudoplastic behaviour with significantly higher apparent viscosity for 40 - 45% CF dispersions, and a desirable consistency to be used in making fried sweets and snacks. The Herschel-Bulkley model described dispersions better at 5 - 20%, while Mizrahi-Berk at 25 - 50%. Hahn Ree-Erying's model described thixotropic behaviours for time-dependent flow; increasing CF concentration from 30 - 50% and increasing storage (G') and loss (G'') modulus in the linear viscoelastic region. However, G' values were dominant over G'' values in the small amplitude region, showing elastic behaviour, whereas viscous behaviour was exhibited in the higher amplitude region. During heating (30 - 80°C) in the temperature sweep test, concentrated samples (30 - 50%) showed a drastic increase in G' and complex viscosity (η*), while in cooling stages (95 - 25°C), a 25% concentration sample resulted in the highest values of G', G'', and η*.

Understanding the impact of water-extractable cereal flour constituents on network formation in gluten-starch dough

Water-extractable cereal flour constituents influence bread loaf specific volume, suggesting a contribution to gas cell (de)stabilization in dough. However, the underlying mechanism remains largely unexplored. We studied the impact of incorporating five cereal flour aqueous extracts in model gluten-starch bread (doughs) on specific volume, dough extensional rheology, and protein extractability changes during bread making. Incorporating wheat, rye, or triticale flour aqueous extracts in gluten-starch doughs increased bread specific volume by 12–17%. There were no changes in dough rheology that could explain this specific volume increase, suggesting that other mechanisms relating to gas cell stabilization might be at play. Incorporating oat flour aqueous extracts decreased bread specific volume by 50%. This negative impact was related to poor dough strain hardening behavior, in turn probably explained by disruption of intermolecular glutenin disulfide bonds, as revealed by chromatography. While this study has provided a novel perspective on the mechanisms by which water-extractable cereal flour constituents influence bread volume, it also demonstrates that the compositional heterogeneity of the flour aqueous extracts needs to be addressed to allow an even better understanding of the role of water-extractable cereal flour constituents in stabilizing gas cells in bread dough.

Air-water interface properties and foam stabilization by mildly extracted lentil protein

Lentil proteins have shown potential as substitutes for animal proteins in foam-based food products, although the mechanisms by which the proteins stabilize the air-water interface are largely unexplored. Here, we systematically studied the air-water interfacial behavior (including adsorption kinetics, and interfacial dilatational and shear rheology), interfacial structures and foaming properties of mildly extracted lentil protein isolate (LPI). We compared these properties of LPI with two animal-based proteins commonly used in food industry, i.e., dairy-derived whey protein isolate (WPI) and egg-derived egg white protein isolate (EPI). The mildly extracted LPI had high protein content (85.2%), high protein solubility (91%) and high nativity, with a globulin-to-albumin ratio of 81:19. LPI adsorbed fast at the air-water interface, showing a foam overrun of 285% that is comparable with WPI and EPI. Although LPI formed interfaces with lower stiffness than EPI, it showed comparable foam half-life time (115 min) with EPI, due to the higher thickness of the interface formed by LPI, which is dominated by lentil globular protein particles with a size around 11 nm. The lentil globular proteins appear to have weaker in-plane interactions than smaller WPI molecules at the air-water interface, resulting in a pronouncedly lower interfacial stiffness and foam half-life time of LPI compared to WPI (295 min). However, the LPI-formed interface is more stretchable than the WPI-formed interface and shows less disruption in both large dilatational and shear deformations. Thus, LPI might have comparable or better performance than WPI in stabilizing foam under processing conditions. Overall, lentil proteins have good foaming properties and could be applied as an animal-based protein replacer in producing foam-based food products.

Properties of Cross‐Linked Poly‐l‐lysine Hydrogels across the Random Coil–Helix Transition

AbstractHydrogels are key components of biological tissues and have applications in biomedicine and commercial industry. Many biological tissues are known to strain harden due to the semiflexible nature of the chains. Here, the mechancial properties of poly‐l‐lysine (PLL) hydrogels, whose network chains undergo a random coil–helix transition, are studied as a function of the polypeptide's structural changes. PLL is cross‐linked with poly(ethylene glycol)diglycidyl ether at cross‐link percents ranging from 3% to 6%. The conformation change and mechanical properties are investigated with circular dichroism and small and large amplitude oscillatory shear rheology, respectively. As a function of pH at low cross‐link percents, a transition from strain softening to strain hardening is observed as the network chains become helical that is similar to the behavior of biological filamentous gels and consistent with recent theoretical descriptions of network strain hardening. At higher cross‐link densities, the hydrogels become brittle due to stress concentration in inhomogeneous locations in the network, which is studied with dynamic light scattering. Overall, the random coil–helix transition has a significant effect on the nonlinear mechanical properties of PLL hydrogels. By understanding the hydrogel structure and response to environmental changes, their potential can be expanded as functional biomedical materials.

Thermomechanical Properties of High Oleic Palm Oil Assessed Using Differential Scanning Calorimetry, Texture Analysis, Microscopy, and Shear Rheology.

Standard Palm Oil (SPO) is widely used as a food ingredient partially due to its unique thermophysical properties. However, the American Heart Association recommends a saturated fat consumption of <5% of the caloric intake per day. The OxG Palm hybrid yields oil known as "palm oil with a higher content of oleic acid" (HOPO), with <35% SFA and >50% oleic acid. Characterizing novel high oleic oils is the starting point to find processes that can functionalize them such as oleogelation. This study compared the thermophysical properties of HOPO to SPO using Differential Scanning Calorimetry, shear rheology, polarized light microscopy, and texture analysis to characterize the differences between these oils. HOPO had a lower onset crystallization temperature (Δ7 °C) and its rheological behavior followed similar trends to SPO; however, large viscosity offsets were observed and were correlated to differences in crystallization temperatures. The maximum peak force of SPO was an order of magnitude higher than that of HOPO. Overall similar trends between the oils were observed, but differences in firmness, crystal morphology, and viscosity were not linearly correlated with the offset in crystallization temperature. This study quantified differences between these oils that will better enable industry to use HOPO in specific applications.

Crystallinity and Oscillatory Shear Rheology of Polyethylene Blends.

Crystallinity and rheological behavior are significant for processing semi-crystalline polymers with fine mechanical properties. There is always an economical need to create a less expensive new material with better properties. Non-isothermal crystallization and oscillatory shear rheology of different branch-type polyethylene-polyethylene blends were investigated. Samples of high-density and low-density polyethylene (HDPE/LDPE) (20/80, 40/60, 60/40 and 80/20 weight ratios) and two types of high-density and linear low-density polyethylene (HDPE/LLDPE) (40/60 and 60/40 weight ratios) were prepared via extrusion. The materials were tested by differential scanning calorimetry (DSC) at several cooling rates (5, 10, 20, 30 and 40°/min) and by oscillation rheometry (ARES G2) at low angular frequency range to prove their miscibility or immiscibility. It was found that the one-peak melting endotherm of the 80-20% HDPE-LDPE blend could indicate miscibility in the solid phase, while the other HDPE-LDPE blends with two-peak curves are partially or not miscible. In contrast, all the HDPE-LLDPE blends indicate co-crystallization, but the 40-60% HDPE-LLDPE butylene blend is probably immiscible. It was revealed that complex viscosity decreases with angular frequency: linearly for HD-LD blends and not linearly for HD-LLDPE blends. The complex viscosity shows linear behavior with composition for HD-LLDPE blends, while there is a positive-negative deviation for HD-LD blends. In the liquid phase, according to rheological measurements, the HDPE-LDPE blends are not or partially miscible, while the HDPE-LLDPE blends are probably miscible.

Can wormlike micelle stiffness be estimated from zero‐shear viscosity? Experimental investigation with a model system and specific salt interactions

AbstractThe microstructure of wormlike micelles (WLM) directly affects the rheological properties of their solutions. Investigating the structure–property relationships of WLM has long been a popular topic for researchers who have developed theoretical and empirical models to describe their viscoelastic behavior. All these models rely on a collection of characteristic “length” parameters that are often difficult to estimate using relatively simple rheological tests. In particular, the micelle stiffness, as described by the persistence length, can be difficult to measure experimentally, while being very impactful on the bulk rheology of WLM solutions. Here, an array of inorganic salts (NaCl, LiCl, MgCl2, NaBr, NaI, and Na2SO4) have been used to induce wormlike micelle formation in an aqueous solution of the surfactant sodium lauryl ether sulfate. Ion dissociation/association with the surfactant head groups and the hydrogen bond network of the water alters the effective stiffness of the micelles, allowing for an estimation of the stiffness using three different methods: (1) small angle neutron scattering (SANS) measurements, (2) oscillatory rheological measurements, and (3) steady rheological measurements with a thermodynamic packing parameter model. Each of these methods are then compared and shown to be consistent with each other for the micelle solutions tested. The consistency of the results across all the measurements suggests that the approach used in this study, which estimates micelle parameters using steady shear rheology and a thermodynamic model, could provide a simpler and more accessible method for estimating micelle parameters in a wide range of surfactant systems.