Oscillatory Shear Tests Research Articles

Distinguishing between Linear and Star Polystyrenes with Unentangled Arms by Dynamic Oscillatory Shear Tests.

Linear and nonlinear viscoelastic properties of star polystyrene (PS) melts with unentangled arms were measured by using small-amplitude and medium-amplitude oscillatory shear (SAOS and MAOS) tests. For comparison purposes, such tests were also conducted on entangled linear and star PS melts. Interestingly, the linear viscoelastic properties of unentangled star PS were quantitatively described using the Lihktman-McLeish model for entangled linear chains, indicating that unentangled stars were indistinguishable from linear chains by using relaxation spectra. By contrast, the relative intrinsic nonlinearity (Q0), one of the MAOS material functions, exhibited a difference between unentangled star and linear PS. When the maximum Q0 value (Q0,max) was plotted against the entanglement number of span molecules (Zs), unentangled star PS exhibited larger Q0,max values than linear PS, which was quantitatively predicted via the multimode K-BKZ model. Therefore, in the unentangled regime, star PS was concluded to be characterized by intrinsically higher relative nonlinearity than linear PS.

A comprehensive assessment for the structural change of waxy crude oils induced by pour point depressant beneficiation

In the petroleum industry, the solid paraffins that precipitate out from a waxy crude oil complicate the low-temperature flow characteristics, causing major difficulties in pipeline transportation. Pour point depressants (PPDs) are often utilized to improve the flow characteristics of crude oils by modifying the morphology and structure of wax crystals, becoming a great technical and economic interest. The improving mechanism of PPDs on the structure of gelled waxy crude oil can be attributed to the nucleation, co-crystallization, and adsorption effect to the precipitated wax crystals, preventing the waxy structure from growing further and forming a volume spanning network. Many previous works about the PPDs’ effect have merely focused on the pour point, apparent viscosity, and yield strength depressing ability, while other structural properties have rarely been comprehensively evaluated. The objective of this study is to comprehensively reveal the change of the wax particle structure in oils benefitted with PPDs. The structure of gelled oils doped with PPDs was found to become less elastic and more susceptible to shear perturbation with a lower linear deformation range of 0.42% and a longer relaxed time scale of 3000 s. Large amplitude oscillatory shear (LAOS) tests show that the nonlinear viscoelastic behaviors can be weakened by PPDs, whereas the third harmonic value obtained by Fourier-transform analysis increases after adding PPDs, indicating that the sensitivity to applied load are strengthened. Meanwhile, the value of yield strain increases to about 8.7%, and the irreversible plastic deformation zone becomes relatively broader (brittleness index I increases to 70.9), which mean a more ductile fracture induced by PPDs would occur when yielding. Although the additive PPDs weaken the structural strength and the non-Newtonian characteristics (kinetic index of n1 increases to 0.8), the characteristic of thixotropy is obviously strengthened, and the doped crude oils exhibit a faster structural breakdown process after yielding. All these novel changes for structural features explored in this paper provide theoretical guidance into understanding the practical engineering problems of accelerated process for the pipeline restart flow benefitted with PPDs.

Comparison of mixing and non-linear viscoelastic properties of carob germ glutelins and wheat glutenin

Carob germ glutelins were compared to wheat glutenin from a rheological standpoint to provide a basis for the possible use of carob germ glutelins as a non-gluten protein in gluten-free dough systems. Molecular weight distributions, mixing and non-linear viscoelastic properties of carob germ glutelins and wheat glutenin were compared, while the impact of mixing on non-linear rheological properties of these protein fractions were evaluated over short (4-min) and long (35-min) mixing times. Development time was 13 min for carob germ glutelins, while reaching 500 BU consistency took 34 min for wheat glutenin, suggesting faster hydration for carob germ glutelins due to their relatively lower molecular weight distribution and more hydrophilic nature. Phase angle values revealed similar linear viscoelastic properties for both proteins after 4-min and 35-min mixing. However, Large Amplitude Oscillatory Shear (LAOS) tests indicated type I non-linear behavior for carob germ glutelins and type III non-linear behavior for wheat glutenin after 35-min mixing at which both proteins had similar consistencies, pointing out to weaker stability for carob germ glutelins when exposed to large deformations. Higher degree of strain stiffening and shear thinning behaviors were found for carob germ glutelins in the non-linear region. Increasing mixing time caused a decrease in the strain stiffening behavior of wheat glutenin under large strain-high frequency deformations, while strain stiffening behavior of carob germ glutelins remained similar. Comparing the mixing and LAOS properties of carob germ glutelins to those of wheat glutenin unraveled the processing needs of dough systems where carob germ glutelins could be used as a non-gluten protein to produce alternative gluten-free baked products with improved quality.

Effect of Mixing Conditions on Dispersion and Degradation Behavior of HDPE/UHMWPE Blends

High density polyethylene (HDPE) / ultra high molecular weight polyethylene (UHMWPE) blend is expected as an all-polyolefin recycle material that can achieve both mechanical properties and a continuous melt-mixing process. In order to improve the mechanical properties of polymer blends, optimal mixing is required to achieve both good dispersibility and low degradation. In this study, the effect of mixing conditions on the dispersion and degradation behavior of HDPE/UHMWPE blends were investigated. Neat HDPE and HDPE with 5% UHMWPE were obtained by melt mixing in internal batch mixer. Time of mixing, Specific Energy Input (SEI), and rotation speed of the rotors were changed. From the results of microscopic observation and a differential scanning calorimetry (DSC), the dispersibility progressed with the increase in SEI regardless of the rotor speed. The results of Gel Permeation Chromatography (GPC) show the molecular chain scission was also promoted by the increase in SEI. In the other hands, the results of oscillatory shear test show the increase in storage modulus G’ were promoted by increase in not only SEI but rotor speed. Furthermore, the molecular chain scission and increase in G’ were significantly suppressed by the nitrogen atmosphere.

Study on dynamic properties of ultrasoft clay based on large amplitude oscillatory shear tests

In offshore engineering, the dynamic properties of ultrasoft clay in the seabed could affect the stability of offshore construction under dynamic loading. The typical rheological response of ultrasoft clay is studied based on the test results from large amplitude oscillatory shear tests with a rheometer. The ultrasoft clay undergoes three phases: the solid phase, transition phase and liquid phase, under dynamic loading. Modulus overshoot is observed when a phase transition occurs. The shear modulus and damping ratio of ultrasoft clay are studied based on the relationship between rheological parameters and dynamic parameters. The results show that the maximum shear modulus of ultrasoft clay could be expressed as a function of water content. Compared with general clay, the normalized shear modulus of ultrasoft clay decreases, and the damping ratio rapidly increases with increasing shear strain. Models describing the change in the normalized shear modulus and damping ratio with the shear strain of ultrasoft clay are suggested based on our test results. This study could aid in the evaluation of the stability of submarine structures at the seabed level under dynamic loading.

Viscoelastic behavior of oral mucosa. A rheological study using small-amplitude oscillatory shear tests

The purpose of this work was to determine the viscoelastic behavior of porcine and human oral mucosa under physiological conditions of temperature, hydration and chewing. The linear elastic and viscous shear moduli of these soft tissues were determined by small-amplitude oscillatory shear (SAOS) tests at masticatory frequency using a stress-controlled rheometer equipped with an immersion cell on punched biopsies 8 mm in diameter. Non physiological conditions of temperature were also used to access other parameters such as the denaturation temperature of collagen.First, the different parameters such as normal force, frequency and maximal strain were adjusted to obtain reliable data on porcine mucosa. The optimal normal force was 0.1N and the linear viscoelastic limit was found for a strain amplitude of 0.5% for both 0.1 and 1 Hz. The storage moduli of porcine mucosa, ranging from 5 to 16 kPa, were in the same range as cutaneous tissues determined by SAOS at equivalent frequencies. The storage modulus, superior to the loss modulus G″, indicates a predominant elastic contribution to shear stress in chewing conditions.Second, this protocol evidenced an influence of the anatomic site of the mouth on the viscoelastic behavior of porcine mucosa, mandibular biopsies having higher storage moduli than maxillary biopsies. Temperature scans showed the mechanical manifestation of collagen denaturation in the 60–70 °C range as previous calorimetric analyses. Finally, this mechanical protocol was successfully adapted to characterize human mucosa in an elderly population. It was shown that the elastic modulus is impacted by local inflammation (gingivitis), decreasing significantly from 6 ± 1.4 kPa to 2.5 ± 0.3 kPa.

Ultrasonic characterization and beyond: How to select a hydrogel for tissue engineering

Hydrogels have emerged as a crucial class of materials within the field of tissue engineering. There is growing interest in matching the mechanical properties of hydrogel scaffolds to tissues in the human body and optimizing these properties for cell growth and differentiation. Gelatin methacrylate (GelMA) is a well-accepted, biocompatible hydrogel with tunable mechanical properties. However, the effects of various formulation parameters on its mechanical properties are not well understood. In this study, an array of GelMA scaffold fabrication parameters is evaluated by varying GelMA concentration and ultraviolet light exposure time. Our overarching goal is to characterize the mechanical properties through ultrasound and rheological measurements, providing a framework for GelMA scaffold selection. Pulse-echo ultrasound techniques were used to non-invasively determine the sound speed and attenuation of the scaffolds, revealing significant dependence on GelMA concentration. Steady shear rate and strain- and frequency-controlled oscillatory shear tests using a rotational rheometer (Model: DHR-2, TA Instruments) revealed a range in the levels of shear-thinning as well as viscoelasticity and showed moduli-dependence on both GelMA concentration and light exposure time. Together, this acoustic and rheological characterization can be used to inform the selection of GelMA scaffolds in tissue engineering applications.

Resilience study of wheat protein networks with large amplitude oscillatory shear rheology

This study investigates the effect of standard laboratory production steps on the network properties of vital gluten. Gluten experiences high mechanical input during production from wheat dough and subsequent processing, which influences the network characteristics. The production of vital gluten in laboratory scale ensures full control on all processing parameters and the possibility to obtain the protein using the mildest washing, drying and milling techniques. Large Amplitude Oscillatory Shear (LAOS) tests were performed on wheat dough, intermediate materials during gluten production and the final product vital gluten at frequencies of 1–15 rad/s and strains from 0.01 to 100%. The elastic and viscous behavior of the material are described by analyzing the fundamental response and the higher harmonics, based on Lissajous-Bowditch curves. The intra-cycle behavior revealed that vital gluten only exhibits network stiffening, whereas dough shows both strain stiffening and shear thinning effects. This suggests that starch induces the shear thinning effects in dough.Comparison of rehydrated and fresh gluten obtained from the same starting material reveals minor alteration of the protein secondary structures during the production process by means of Fourier-transform infrared spectroscopy (FTIR). A pronounced difference in water uptake accounts for modified rheological network properties.

Rheological Performance of High-Temperature-Resistant, Salt-Resistant Fracturing Fluid Gel Based on Organic-Zirconium-Crosslinked HPAM

Development of low-cost, high-temperature-resistant and salt-resistant fracturing fluids is a hot and difficult issue in reservoir fluids modification. In this study, an organic zirconium crosslinker that was synthesized and crosslinked with partially hydrolyzed polyacrylamide (HPAM) was employed as a cost-effective polymer thickener to synthesize a high-temperature-resistant and salt-resistant fracturing fluid. The rheological properties of HPAM in tap water solutions and 2 × 104 mg/L salt solutions were analyzed. The results demonstrated that addition of salt reduced viscosity and viscoelasticity of HPAM solutions. Molecular dynamics (MD) simulation results indicated that, due to electrostatic interaction, the carboxylate ions of HPAM formed an ionic bridge with metal cations, curling the conformation, decreasing the radius of rotation and thus decreasing viscosity. However, optimizing fracturing fluids formulation can mitigate the detrimental effects of salt on HPAM. The rheological characteristics of the HPAM fracturing fluid crosslinking process were analyzed and a crosslinking rheological kinetic equation was established under small-amplitude oscillatory shear (SAOS) test. The results of a large-amplitude oscillation shear (LAOS) test indicate that the heating effect on crosslinking is stronger than the shear effect on crosslinking. High-temperature-resistant and shear-resistant experiments demonstrated good performance of fracturing fluids of tap water and salt solution at 200 °C and 180 °C.

Incorporating chitin nanocrystal yields stronger soy protein gel: Insights into linear and nonlinear rheological behaviors by oscillatory shear tests

Chitin nanocrystals (ChNs) were successfully fabricated from shrimp and their effects on the microstructure and gelling properties of glucono-δ-lactone-induced soy protein isolate (SPI) were investigated. Firstly, transmission electron microscopy (TEM) showed that the average length and width of ChNs were 208.8 nm and 19.2 nm, respectively. The zeta potentials of ChNs changed from +38.6 mV at pH 3.0 to +16.4 mV at pH 8.0. Subsequently, the gel strength, water holding capacity (WHC) and viscoelasticity of the composite gels were improved by increasing the ChNs concentration from 0 to 1.0% (w/v). Based on low field nuclear magnetic resonance (LF-NMR) analysis, the decrease in PT 22 and increase in PT 21 indicated that the improvement of WHC was associated with the transformation of free water into immobilized water. Scanning electron microscopy (SEM) showed that the incorporation of ChNs promoted the formation of a denser and more homogenous gel network. All composite gels showed high frequency dependence and a typical Type I (strain thinning) network behavior. The increase in both elastic and viscous moduli further showed the improvement in the microstructure of composite gels, which was induced by the addition of ChNs. The Sequence of Physical Processes (SPP) analysis provided a detailed deformation history of gel microstructure by the evolution of the instantaneous storage (G′t) and loss moduli (G″ t ). In this method, gel samples experienced various degrees of microstructural rearrangements at small amplitude oscillatory shear (SAOS) region (γ = 0.64%) and large amplitude oscillatory shear (LAOS) region (γ = 100%). • Formation of stronger SPI gels through incorporation of ChNs. • ChNs increased the gel strength, WHC and viscoelasticity of SPI gels. • ChNs provided a denser and more uniform microstructure for SPI gels. • All gels showed high frequency dependence and type I behavior. • The gel microstructure showed stepwise changes during large deformation.

Identification of the effect of ionizing radiation on epichlorohydrin-based homo-, co-, and ter-polymers

In this study, the effects of ionizing radiation on a series of epichlorohydrin (ECH)-based polymers, namely poly(epichlorohydrin) (CO) homopolymer, poly(epichlorohydrin-co-ethylene oxide) (ECO) copolymer, and poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO) terpolymer, were examined. Polymers are irradiated at room temperature with accelerated electrons in the 0–150 kGy absorbed dose range. The effect of irradiation on the chain structure polymers was examined with sol-gel and rheological analyses. While ECH-based homo- and co-polymers showed crosslinking up to a specific dose, it was found that chain scission above a critical dose value was more dominant. On the other hand, in the ECH terpolymer, crosslinking tendency in the 0–80 kGy dose range was found to be dominant over chain scission. It was found that radiation stability varies depending on the initial molecular mass of the copolymer. Using the Charlesby–Pinner and Charlesby–Rosiak equations for each polymer, the chain scission and crosslink yield ratio (p0/q0), gelation dose (Dg), and virtual gelation dose (Dv) were determined and the effect of ionizing radiation on these polymers, which has increased in use in recent years, was examined. In this study, the effect of ionizing radiation on the long-chain branching value of ECH-based polymers was also examined using a rubber process analyzer (RPA) and large amplitude oscillatory shear testing (LAOS), and a mechanism for the exchange of branching has been proposed.

Nonlinear rheological properties of Chinese cold skin noodle (liangpi) and wheat starch gels by large amplitude oscillatory shear (LAOS)

The recipe secret of making Chinese cuisine cold skin noodles (liangpi) with wheat flour was revealed by linear and nonlinear rheological characterization of wheat starch gel systems, which were made from different concentrations of liangpi slurry (LPS) and wheat starch slurry (WSS). The peak viscosity of LPS was suppressed at low concentrations and significantly higher than that of WSS at high concentrations. The G′ and G″ of LPS gels were higher than that of WSS gels under the same concentration, while the tanδ values were low in LPS gels and exhibited relatively greater mobility. This difference in LPS may be related to the non-starch components in it. The two starch gel systems were further characterized by the large amplitude oscillatory shear (LAOS) test. Lissajous curves showed that LPS gels follow a highly different elastic and viscous evolution than WSS gels during large deformation cycles. This was also evidenced by more pronounced strain stiffening and shear thickening trends of LPS gels and the larger I3/I1 values. The introduction of non-starch components was responsible for the significant changes in the properties of starch gels, and the LAOS method helped us to better understand these differences.

Super stable Melaleuca alternifolia essential oil Pickering emulsions stabilized with cellulose nanofibrils: Rheological aspects

Melaleuca alternifolia essential oil (MaEO) has attracted technological interest in the pharmaceutical, cosmetic and food sectors for its outstanding and broad antimicrobial spectra. However, its active components are highly susceptible to oxidation due to weathering. Therefore, stabilization of the MaEO components is essential. In this work, we evaluated the stability and rheology of MaEO-in-water Pickering emulsions using cellulose nanofibrils (CNF) as an eco-friendly and sustainable stabilizing agent. Small amplitude oscillatory shear (SAOS) tests brought exciting information about the relationship between internal microstructure strength and the relaxation processes, retardation processes, and viscous flow behavior of the emulsions. Measurements of oil droplet diameter distribution and steady-state rheological tests indicate that the emulsions have super stability under static environmental conditions within 28 storage days. Also, the emulsions present steady-state viscosity suitable for applications in dysphagic foods, presenting a pronounced shear-thinning behavior appropriate to developing cream and lotion skin-care eco-friendly products for the human body.

Nonlinear rheological performance characterization of styrene-butadiene-styrene and crumb rubber composite modified bitumen using large amplitude oscillatory shear tests

The crumb rubber (CR) recycled from waste tires can improve the mechanical properties of bitumen effectively. For the widely used modified bitumen today, it could work in nonlinear regime in many occasions. This study focuses on the nonlinear properties of styrene-butadiene-styrene (SBS) and CR composite modified bitumen (CMB) by analyzing the results of stress-controlled large amplitude oscillatory shear (LAOS) tests. The results show that the nonlinearity of SBS/CR CMB was significant under low load frequency, high temperature and high stress level. Lissajous curves at these conditions are distorted obviously due to the presence of higher-order harmonics. By analyzing the geometry parameters of Lissajous curves, it can be concluded that the incorporation of CR has a positive influence on the nonlinear properties of bitumen, which effectively improve the stress bearing capacity of bitumen. However, the high-order harmonic analysis indicates that improving the CR content simply does not always improve the performance of bitumen. Besides, the nonlinearity of SBS/CR CMB with lower CR content is similar to that of SBS modified bitumen through the value of I3/I1 and intrinsic nonlinear parameter Q, thus there are two critical CR contents for the prospect of modifying the nonlinearity of bitumen.

Effect of the Welan Gum Concentration on the Rheological and Structural Behaviour of Biocomposite Hydrogels with Sepiolite as Filler.

A very positive and effective approach to tuning the mechanical properties of polymers has been the development of composites. This paper deals with novel biocomposite hydrogels composed by two biocompatible materials: welan gum as biopolymer matrix and sepiolite as filler. Welan gum content was studied as a tuning parameter to control the rheological properties of the developed biocomposites. The rheological and microstructural behaviour of the composites was investigated by mean of steady-state flow curves, creep-recovery tests, small amplitude oscillatory shear tests, and electron microscopy. An increase in welan gum content provoked the progressive disappearance of the shear-thinningzero-shear-thinning behaviour with a yield point which was clearly defined, characteristic of sepiolite gels, leading to a conventional shear-thinning behaviour, typical of polymeric systems. Also, a higher content of biopolymer in the mixtures led to a more elastic and compact structure characterized by higher values of both G' and G". The fundamental novelty was based on taking the flowability provided by the biopolymer as the main objective and reinforcing the viscosity yielded by welan gum with sepiolite, which contributed to increasing the biocomposite consistency. Thus, rheological properties can be adjusted, taking into account the balance of the components to adapt them to the requirements of each application.

Influence of Magnetic Field and Temperature on Rheological Behavior of Magnetorheological Gel.

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium.

Hemicellulose-bacterial cellulose ribbon interactions affect the anisotropic mechanical behaviour of bacterial cellulose hydrogels

The aim of this study is to investigate the effect of hemicellulose-cellulose interactions on the anisotropic structure of the bacterial cellulose (BC) ribbon network. BC-arabinoxylan (BC-AX) and BC-mixed linkage glucan (BC-MLG) composites were prepared. The mechanical/rheological behaviour was evaluated by compression combined with small amplitude oscillatory shear (SAOS) and stress-relaxation tests. Microscopy revealed that the BC ribbons tended to orient parallel to the liquid/air interface. AX and MLG gathered on the surface of cellulose ribbons but had limited influence on the crystallinity of BC. BC hydrogels showed direction-dependent mechanical properties in compression and stress-relaxation tests. The peak compressive modulus of the tangential BC sample (compressed towards the side of the sample) was over 1000 kPa, whereas for the normal sample (compressed towards the top of sample) the value was only 280 kPa. The relaxation ability of the tangential sample was 48% lower than the normal sample at 1% compression ratio. AX and MLG reduced the anisotropic behaviour of the native BC in normal/tangential compression and stress-relaxation tests, especially in the highly-compressed composites. However, the rheological behaviour of BC and the composites was comparatively isotropic in SAOS. This study is beneficial for further understanding of the contribution of hemicelluloses to the mechanical properties of BC hydrogels, and may promote the application of BC-based materials in food and medical industries.

Structure-rheology relationship in monoolein liquid crystals

Hypotheses: Monoolein liquid crystals find use in foods and pharmaceuticals. Our hypotheses were: (a) liquid crystal symmetry dominates yielding and large deformation, and (b) strain rate frequency superposition (SRFS) may be used to determine mesophase long and short relaxation times.Experiments: Liquid crystal microstructure and rheology were characterised as a function of temperature and composition. Their structure was assessed using small angle X-ray scattering (SAXS) and polarised light microscopy. Small and large deformation rheology was characterised using frequency and amplitude sweeps, large amplitude oscillatory shear tests, and SRFS.Findings: We have contributed to the structure-rheology relationship governing the properties of the lamellar, cubic, and hexagonal mesophases. Initially, we characterised a number of monoolein-water binary phase transitions, which showed similar behaviour with earlier efforts. Frequency sweeps revealed that the cubic phases had the highest elasticity followed by the lamellar and hexagonal phases. The stiffening and thickening ratios, extracted from the Lissajous-Bowditch plots, were used to quantify intra-cycle non-linearities. The cubic phases displayed abrupt yielding with more pronounced stiffening and thinning behaviour compared to the others. Each liquid crystal phase displayed unique rheological behaviour upon large deformation and, by linking rheology with SAXS and composition, we show that their symmetry defined their rheology.

Influence of Type and Concentration of Biopolymer on β-Carotene Encapsulation Efficiency in Nanoemulsions Based on Linseed Oil.

Many lipophilic active substances, such as β-carotene, are sensitive to chemical oxidation. A strategy to protect these ingredients is encapsulation using nanoemulsions. This work analyzes the relationship between the physical stability and encapsulation efficiency of nanoemulsions based on linseed oil. The role of two different polysaccharides, Advanced Performance xanthan gum (APXG) or guar gum (GG) as stabilizers at different concentrations were studied to reach the required physical stability of these systems. This was investigated by means of droplet size distributions, steady-state flow curves, small amplitude oscillatory shear tests, multiple light scattering, and electronic microscopy. The overall results obtained reveal a depletion flocculation mechanism in all the APXG nanoemulsions, regardless of the concentration, and above 0.3 wt.% for GG nanoemulsions. Moreover, it has been demonstrated that enhanced physical stability is directly related to higher values of encapsulation efficiency. Thus, the nanoemulsion formulated with 0.2 wt.% GG, which presented the lowest creaming degree conditioned by depletion flocculation, showed a relative β-carotene concentration even above 80% at 21 days of aging time. In conclusion, the adequate selection of polysaccharide type and its concentration is a key point for the application of stable nanoemulsions as vehicles for active ingredients.

Fortification of Wheat Bread with Edible Chrysanthemum (Chrysanthemum morifolium Ramat.): Unraveling the Mechanisms of Dough Rheology and Bread Quality Changes

The inclusion of plant material in bread formulations is a global trend, but research on the mechanisms of its effect on the structural and baking performance of the dough is lacking. Herein, edible chrysanthemum (Chrysanthemum morifolium Ramat.) powder (CP) was substituted for wheat flour at 3–15 wt% and its effects on dough structure and rheology, bread physicochemical properties, and aroma profile were investigated. The inclusion of CP reduced the relative crystallinity and structure orderliness of starch in terms of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analysis. Steady-state shear and oscillation tests showed that the inclusion of CP resulted in an enhanced viscoelastic behavior of dough, implying an increase in the resistance of the dough system to flow and deformation, which caused a decrease in specific volume and softness of bread compared to the control (bread without CP). The large oscillatory amplitude oscillation shear (LAOS) tests indicated that doughs exhibited I behavior (strain thinning). The scanning electron microscopy (SEM) observation further confirmed these findings. Significantly, formulations with 3 and 6 wt% CP not only improved the rheological and structural properties of doughs but also enriched the aroma profile of bread compared to the control. Furthermore, sensory evaluators reported that bread enriched with 6% CP scored highest in appearance, texture, and overall acceptability, meaning a product with a high sensory appeal to consumers. This work provides valuable information for an in-depth study of the relationship between bread quality and the rheological behavior and structural properties of the dough.