Shear Storage Modulus Research Articles

Mesenchymal Stem Cells Sense the Toughness of Nanomaterials and Interfaces.

Stem cells are known to sense and respond to the mechanical properties of biomaterials. In turn, cells exert forces on their environment that can lead to striking changes in shape, size and contraction of associated tissues, and may result in mechanical disruption and functional failure. However, no study has so far correlated stem cell phenotype and biomaterials toughness. Indeed, disentangling toughness-mediated cell response from other mechanosensing processes has remained elusive as it is particularly challenging to uncouple Youngs' or shear moduli from toughness, within a range relevant to cell-generated forces. In this report, it is shown how the design of the macromolecular architecture of polymer nanosheets regulates interfacial toughness, independently of interfacial shear storage modulus, and how this controls the expansion of mesenchymal stem cells at liquid interfaces. The viscoelasticity and toughness of poly(l-lysine) nanosheets assembled at liquid-liquid interfaces is characterised via interfacial shear rheology. The local (microscale) mechanics of nanosheets are characterised via magnetic tweezer-assisted interfacial microrheology and the thickness of these assemblies is determined from in situ ellipsometry. Finally, the response of mesenchymal stem cells to adhesion and culture at corresponding interfaces is investigated via immunostaining and confocal microscopy.

Effect of Fibrillization pH on Gelation Viscoelasticity and Properties of Biofabricated Dense Collagen Matrices via Gel Aspiration-Ejection.

Reconstituted hydrogels based on the self-assembly of acid-solubilized collagen molecules have been extensively used as in vitro models and precursors in biofabrication processes. This study investigated the effect of fibrillization pH-ranging from 4 to 11-on real-time rheological property changes during the gelation of collagen hydrogels and its interplay with the properties of subsequently biofabricated dense collagen matrices generated via automated gel aspiration-ejection (GAE). A contactless, nondestructive technique was used to characterize the temporal progression in shear storage modulus (G', or stiffness) during collagen gelation. There was a relative increase in G' of the hydrogels from 36 to 900 Pa with an increase in gelation pH. Automated GAE, which simultaneously imparts collagen fibrillar compaction and alignment, was then applied to these precursor collagen hydrogels to biofabricate native extracellular matrix-like densified gels. In line with viscoelastic properties, only hydrogels fibrillized in the 6.5 < pH ≤ 10 range could be densified via GAE. There was an increase in both fibrillar density and alignment in the GAE-derived matrices with an increase in gelation pH. These factors, combined with a higher G' in the alkaline precursor hydrogels, led to a significant increase in the micro-compressive modulus of GAE-densified gels of pH 9 and 10. Furthermore, NIH/3T3 fibroblast-seeded GAE-derived matrices densified from gels fibrillized in the pH range of 7 to 10 exhibited low cell mortality with >80% viability. It is anticipated that the results of this study can be potentially applicable to other hydrogel systems, as well as biofabrication techniques involving needles or nozzles, such as injection and bioprinting.

Impact of chemical and rheological properties on 3D printability and starch digestibility of potato pastes from different cultivars

SummaryPotato paste is a potential material for 3D food printing owing to its high printability. The objective of this study was to investigate the effects of potato characteristics on the printability of 3D food printer and starch digestibility, using potato pastes prepared from six potato cultivars with a wide range of cooking properties. The potato sample with the lowest starch content, peak viscosity and hardness of the printed products showed high levels of printability, including smoothness and formability. The difference in yield stress determined by stress sweep test reflected the variation in printability among potato cultivars. Potato samples with higher quality of smoothness and formability of the printed products showed a lower yield stress (968–1980 Pa), whereas those with poor printability showed relatively higher yield stress (3072–3167 Pa). The potato sample with the highest amylose content, setback viscosity and storage shear modulus demonstrated the lowest rapidly digestible starch (69.3%) and highest content of undigested starch after 120 min incubation (24.2%). The chemical and rheological properties of potato were shown to play important roles in improving the printability and nutritional value of paste as ink.

Glucose biosensors based on Michael addition crosslinked poly(ethylene glycol) hydrogels with chemo-optical sensing microdomains.

Continuous glucose monitoring (CGM) devices have the potential to lead to better disease management and improved outcomes in patients with diabetes. Chemo-optical glucose sensors offer a promising, accurate, long-term alternative to the current CGMs that require frequent calibration and replacement. Recently, we have proposed glucose sensor designs using phosphorescence lifetime-based measurement of chemo-optical glucose sensing microdomains embedded within alginate hydrogels. Due to the poor long-term stability of calcium-crosslinked alginate, we propose poly(ethylene glycol) (PEG) hydrogels synthesized via thiol-Michael addition chemistry as an alternative hydrogel carrier. The objective of this study was to evaluate the suitability of Michael addition crosslinked PEG hydrogels compared to calcium crosslinked alginate hydrogels for encapsulating glucose-sensing microdomains. PEG hydrogels crosslinked via thiol-vinyl sulfone addition achieved gelation in under 5 minutes, resulting in an even distribution of sensing microdomains. The shear storage modulus of the PEG hydrogels was tunable from 2.2 ± 0.1 kPa to 9.5 ± 1.8 kPa, which was comparable to the alginate hydrogels (10.5 ± 0.8 kPa), and the inclusion of microdomains did not significantly impact stiffness. The high water content of PEG hydrogels resulted in high glucose permeability that closely corresponded to the glucose permeability of alginate (D = 0.09 and 0.12 cm2 s-1, respectively; p = 0.47), but the PEG hydrogels exhibited superior stability. Both PEG and alginate-embedded sensors exhibited a sensing range up to ∼200 mg dL-1 glucose. The lower limits of detection (LOD) for PEG and alginate-based glucose sensors were 19.8 and 20.6 mg dL-1 with a difference of just 4.2% variation. The small difference between PEG and alginate embedded sensors indicates that their sensing properties are primarily determined by the glucose sensing microdomains rather than the hydrogel matrix. Overall, the results of this study indicate that Michael addition-crosslinked PEG hydrogels are a promising platform for encapsulation of chemo-optical glucose sensing microdomains.

Interfacial Properties of Pea Protein Hydrolysate: The Effect of Ionic Strength

The effect of a tryptic hydrolysis as well as the effect of ionic strength (0–0.4 M NaCl) was investigated on the oil/water interfacial properties of soluble pea protein hydrolysate (SPPH) at neutral pH and room temperature (20 ± 0.01 °C). SEC-MALS and SDS-Page analysis showed that tryptic hydrolysis created a lower molecular weight polypeptide mixture, whereas FTIR analysis and DSC thermograms demonstrated a more disordered and flexible structure. The bulk properties of SPPH were studied in terms of hydrodynamic diameter and turbidity, where higher particle size (+ ~13 nm) and turbidity were observed at 0.4 M NaCl. Regarding the interfacial properties, the surface activity of SPPH improved by increasing ionic strength, with maximum interfacial pressure (14.28 mN/m) at 0.4 M NaCl. Nevertheless, the addition of NaCl negatively affected the elasticity and strength of the interfacial film, where the sample without salt exhibited the highest dilatational and shear storage modulus in all the frequencies considered.

Preparation and magneto-mechanical properties of 3D microporous magnetorheological foam

Magnetorheological (MR) materials with excellent magneto-mechanical properties have great application values in the field of vibration reduction and buffering. By combining the advantages of light weight and excellent energy absorption of porous polymer materials, the development of porous MR materials can improve the buffer performance of MR technology. In this paper, we proposed a one-step method for fabricating the 3D microporous MR foam based on polyurethane matrix. Micromorphology of MR foam character by scanning electron microscope shows the existence of a 3D network structure with embedded carbonyl iron particles (CIPs). The unique 3D microporous structure ensures the excellent magneto-mechanical properties of MR foam. The test results analyzed by a rheometer reveal that its compressive modulus and shear storage modulus enhanced significantly with the magnetic field. The influence factors such as CIP content, shear frequency, and shear strain have been systematically studied under the oscillating shear mode. It indicated that the MR foam exhibits obvious viscoelasticity, the dynamic modulus depends on the shear frequency and shear strain, and it has excellent magneto-mechanical properties. This work can provide a new technical solution for fabrication of MR porous materials for MR buffer technology.

The Effect of Various Polyhedral Oligomeric Silsesquioxanes on Viscoelastic, Thermal Properties and Crystallization of Poly(ε-caprolactone) Nanocomposites

Polyhedral oligomeric silsesquioxane POSS nanoparticles can be applied as reinforcing additives modifying various properties of biodegradable polymers. The effects of aminopropylisobutyl POSS (amine-POSS), trisilanolisooctyl-POSS (HO-POSS) and glycidyl-POSS (Gly-POSS) on the viscoelastic, thermal properties and crystallization of biodegradable poly(ε-caprolactone) PCL were studied. The analysis of the viscoelastic properties at ambient temperature indicated that aminopropylisobutyl POSS (amine-POSS) and glycidyl-POSS (Gly-POSS) enhanced the dynamic mechanical properties of PCL. The increase in the storage shear modulus G' and loss modulus G″ was observed. The plasticizing effect of trisilanolisooctyl POSS (HO-POSS) due to the presence of long isoctyl groups was confirmed. As a result, the crystallization of PCL was facilitated and the degree of crystallinity of χc increased up to 50.9%. The damping properties and the values of tan δ for PCL/HO-POSS composition increased from 0.052 to 0.069. The TGA results point out the worsening of the PCL thermal stability, with lower values of T0.5%, T1% and T3%. Both HO-POSS and Gly-POSS facilitated the relaxation of molten PCL. The presence of Gly-POSS influenced the changes that occurred in the viscoelastic properties of the molten PCL due to the thermo-mechanical degradation of the material; a positive impact was observed.

Identification of the viscoelastic properties of a hydrogel in sol–gel transition by vibration experiments

Soft viscoelastic materials, such as hydrogels, are widely used by biomedical and agri-food industries. The characterization of their transition from solution (liquid) to gel (solid) state is often necessary for manufacturing processes and quality control. This study aims at characterizing the viscoelastic properties of a hydrogel in sol–gel transition by measuring the vibration response of the bottom silicone membrane of a rigid circular cylindrical container subjected to base excitation. The static deflection of the membrane for increasing sample filling height was measured. The frequency-responses of the membrane alone and of the membrane coupled to a hydrogel during sol–gel transition were measured for increasing filling heights. A finite-element numerical model was built for the identification of the storage shear modulus and loss tangent of the hydrogel. Both a slip and a no-slip conditions of the hydrogel at the inner wall of the container were applied and their effects were compared. The static deflection was calculated and compared to the experiments. The parameters of a dynamic model of the coupled membrane–hydrogel were identified. The evolution of the identified material parameters enables to follow the sol–gel transition of the hydrogel. Results show that the membrane vibration can be used to characterize the viscoelastic mechanical properties of a hydrogel in sol–gel transition through a more versatile approach.

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.

Auxetic behavior and unusual shear resistance of crumpled materials: Opportunities for programming the nonlinear responses of crumpled mechanical metamaterials

Crumpled systems (CSs) can be used as building blocks of mechanical metamaterials with low sensitivity to defects. But to exploit the potential of CSs for novel applications, extensive understanding of the physics of these systems is needed and, so far, the shear response of CSs has not been studied. Here we study the shear response of CSs via short/large amplitude oscillatory shear (SAOS/LAOS) while investigating the effect of several parameters. The training of crumpled paper reduced long-range correlations and resulted in an increase of the shear modulus with compaction, not observed for untrained paper. The presence of stacked layers parallel to the shear direction, in contrast to those positioned perpendicularly, resulted in lower shear storage modulus and increased energy dissipation through layers sliding. Reducing the surface friction allowed for easier internal rearrangements during shear deformations. In general, the shear resistance increases less with the increasing level of compaction than the compaction stiffness. However, it can be tuned by friction between the layers and their orientation. The estimated Poisson’s ratio of CSs reveals their auxetic nature. Our results pave the way to better understand the full mechanical response of CSs and tune their desired properties for practical applications.

Protein-based biochars as potential renewable fillers in styrene-butadiene rubber composites

In this study, chicken feather meal (CFM) and canola protein (CP) were converted into biochar and their suitability as reinforcing fillers in styrene-butadiene rubber (SBR) composites was evaluated. The protein-based feedstocks were pyrolyzed at 700 °C for 1 h, at a heating rate of 50 °C/min under different pyrolysis atmospheric conditions (N2, CO2, and steam). The flow rate of N2 and CO2 was 700 ml/min, while that of steam was 31 ml/min. Also, biochar was produced under N2 and CO2 gas flow and subsequently activated using steam. The physicochemical properties of the resulting CFM and CP biochars were characterized based on elemental and proximate analyses, surface area, Fourier-transform infrared spectroscopy (FTIR), and thermal field emission scanning electron microscopy. Results showed that activated CP, pyrolyzed under nitrogen and subsequently steam cooled (CP N2 + SC), had enhanced physicochemical properties such as lower ash content, higher fixed carbon content, and reduced polar surface functional groups compared to the other studied biochars in this study. Results also showed that CFM and CP pyrolyzed under nitrogen and subsequently steam cooled displayed higher final moduli and better filler dispersion in rubber than the other biochar samples produced in this study. Given that results showed favorable physicochemical properties and higher final moduli for CP N2 + SC, this sample was further tested using dynamic mechanical analysis (DMA) and results showed slight differences with carbon black regarding the temperature dependence of the shear storage modulus (G′) and the loss tangent (tan δ). These differences were attributed to increased filler-filler interactions, reduced filler-rubber interactions, and a lower dispersion in rubber than carbon black. The observed differences were not large enough to explain the inability of the biochar to adequately reinforce the rubber. However, the biochar filled rubber sample had a comparable viscoelastic behavior to carbon black over the studied temperature range.

The effect of adhesive amount and type on failure mode and shear strength of glued timber-concrete joints

Wet and dry bonding techniques were used to bond the spruce timber and concrete with the adhesive as a timber-concrete joint (TCJ) in this study. This paper discusses the effect of adhesive amount and type, i.e., polyurethane and epoxy, on the bond strength of wet and dry TCJs. Adhesive amounts (i.e., quantified with equivalent thicknesses) for the polyurethane were 0.25-, 1- and 3-mm, and for epoxy 1-, 2- and 3-mm. For the wet TCJ, the hardener and resin of two-component polyurethane and epoxy were blended and applied to the spruce timber. Afterward, cast-in-place concrete was cast on the timber substrates with the delayed time (waiting time) of T0, TGEL2, and TGEL. According to the oscillation test, the gel time of adhesive (TGEL) was 72 and 221 min for the polyurethane and epoxy, respectively. A double lap shear test was run to the wet and dry timber-concrete joints to analyze the influence of adhesive amount and type on their failure modes and bond strength. Experiments indicated that increasing the adhesive thickness (or amount) of wet TCJs resulted in larger shear strength of the joints. A longer delayed time improved the bond strength of wet TCJ glued with 1- and 3-mm polyurethane equivalent thicknesses. However, with a similar amount of adhesive, the bond strength of wet TCJ glued with epoxy decreased with a longer delayed time. This behavior was attributed to differences in shear storage modulus of used polyurethane (G’=1.2 kPa) and epoxy (G’=229.7 kPa) adhesives at T0 delayed time. It was found that the wet bonding technique used to produce TCJs tended to have higher shear strength than the dry bonding technique for the given same adhesive amount and type.

A generalized mixture rule for estimating the effective modulus of cement paste in early age

PurposeThe purpose of this paper is to obtain a theoretical model to analyze the effective modulus of cement paste in early age, including the setting and hardening periods, which has a great impact on mechanical properties of concrete structure.Design/methodology/approachBased on a power law approximation, a generalized mixture rule is used to construct the relationship between the effective modulus and hydration degree. In addition, a new model of the dependence of the Poisson's ratio on the hydration degree and water cement ratio is proposed for cement paste in early age.FindingsThe effective Young's modulus, storage shear modulus and Poisson's ratio of cement pastes with different water cement ratios and hydration degrees are studied by the presented model. The model can be applied to simulate the behavior of early-age cement paste at both the setting and the hardening periods. Compared with the experimental results, the correctness of the model is validated.Originality/valueThis work presents a mathematical model that can effectively estimate the effective Young's modulus and Poisson's ratio in the hardening period, and the storage shear modulus in the setting period of cement pastes.

Preparation of CF-GO-SiO2 multi-scale reinforcements based on electrostatic interaction: A non-destructive and simple method to construct hybrid interface layers of carbon fiber reinforced thermoplastic resin composites

A GO-SiO2 hybrid interface layer was prepared by electrostatic adsorption to synergistically improve the weak interface bonding between carbon fiber (CF) and poly(phthalazinone ether ketone) (PPEK). FTIR, Raman and XPS confirmed that GO-SiO2 interface layer is constructed on CF surface. SEM and AFM indicated that the synergistic effect of GO-SiO2 could obviously improve the CF surface roughness. CF-GO-SiO2/PPEK composite exhibits excellent interlaminar shear strength (84.2 MPa), flexural strength (1620 MPa), storage modulus (132.9 GPa) and Tg (285 °C). The GO-SiO2 interface layer improves the mechanical interlocking and wettability between CF and PPEK, and the failure mechanism of the composite changes from interfacial debonding for Untreated CF/PPEK composite to matrix cohesive destruction and fiber breakage for CF-GO-SiO2/PPEK composite. Moreover, the layer is beneficial to the hydrothermal ageing resistance of the composite. This study provides a promising strategy for improving the interfacial properties of advanced thermoplastic composites.

Effect of corneal collagen crosslinking on viscoelastic shear properties of the cornea

The cornea is responsible for most of the refractive power in the eye and acts as a protective layer for internal contents of the eye. The cornea requires mechanical strength for maintaining its precise shape and for withstanding external and internal forces. Corneal collagen crosslinking (CXL) is a treatment option to improve corneal mechanical properties. The primary objective of this study was to characterize CXL effects on viscoelastic shear properties of the porcine cornea as a function of compressive strain. For this purpose, corneal buttons were prepared and divided into three groups: control group (n = 5), pseudo-crosslinked group (n = 5), and crosslinked group (n = 5). A rheometer was used to perform dynamics torsional shear experiments on corneal disks at different levels of compressive strain (0%–40%). Specifically, strain sweep experiments and frequency sweep tests were done in order to determine the range of linear viscoelasticity and frequency dependent shear properties, respectively. It was found that the shear properties of all samples were dependent on the shear strain magnitude, loading frequency, and compressive strain. With increasing the applied shear strain, all samples showed a nonlinear viscoelastic response. Furthermore, the shear modulus of samples increased with increasing the frequency of the applied shear strain and/or increasing the compressive strain. Finally, the CXL treatment significantly increased the shear storage and loss moduli when the compressive strain was varied from 0% to 30% (p < 0.05); larger shear moduli were observed at compressive 40% strain but the difference was not significant (P = 0.12).

Comparison of Crosslinking Kinetics of UV-Transparent Ethylene-Vinyl Acetate Copolymer and Polyolefin Elastomer Encapsulants.

Encapsulants based on ethylene-vinyl acetate copolymers (EVA) or polyolefin elastomers (POE) are essential for glass or photovoltaic module laminates. To improve their multi-functional property profile and their durability, the encapsulants are frequently peroxide crosslinked. The crosslinking kinetics are affected by the macromolecular structure and the formulation with stabilizers such as phenolic antioxidants, hindered amine light stabilizers or aromatic ultraviolet (UV) absorbers. The main objective of this study was to implement temperature-rise and isothermal dynamic mechanical analysis (DMA) approaches in torsional mode and to assess and compare the crosslinking kinetics of novel UV-transparent encapsulants based on EVA and POE. The gelation time was evaluated from the crossover of the storage and loss shear modulus. While the investigated EVA and POE encapsulants revealed quite similar activation energy values of 155 kJ/moles, the storage modulus and complex viscosity in the rubbery state were significantly higher for EVA. Moreover, the gelation of the polar EVA grade was about four times faster than for the less polar POE encapsulant. Accordingly, the curing reaction of POE was retarded up to a factor of 1.6 to achieve a progress of crosslinking of 95%. Hence, distinct differences in the crosslinking kinetics of the UV-transparent EVA and POE grades were ascertained, which is highly relevant for the lamination of modules.

Modulus and adhesion of Sylgard 184, Solaris, and Ecoflex 00‐30 silicone elastomers with varied mixing ratios

AbstractTwo‐part, commercial silicone elastomers are used in a variety of fundamental soft materials research and industrial applications due to their wide availability, ease of use, low cost, and mechanical tunability. This work seeks to create a library of moduli for three common elastomer systems with varied mixing ratios: Sylgard 184, Solaris, and Ecoflex 00–30, as well as provide a comparison of their adhesive properties. Shear storage moduli are quantified using parallel plate oscillatory shear rheology. The work of debonding is measured with spherical probe adhesion testing, and the static, advancing, and receding contact angles are measured via goniometer. Sylgard 184 can have shear moduli ranging from ~0.5 kPa‐620 kPa, Solaris from ~0.6 kPa‐175 kPa, and EF from ~1.3 kPa‐35 kPa measured at a frequency of 0.01 rad/s. In general, increasing mixing ratios creates softer samples. Additionally, softer samples are universally more adhesive, regardless of the material system. When comparing the different material systems, Sylgard 184 is generally the most adhesive, followed closely by Solaris, and then by Ecoflex 00–30. Our study offers a baseline dataset of modulus values and comparative adhesion to help researchers determine an appropriate commercial silicone for their application.

In Vitro Evaluation of Real-Time Viscoelastic and Coagulation Properties of Various Classes of Topical Hemostatic Agents Using a Novel Contactless Nondestructive Technology.

Hemorrhaging is the main cause of death among combat and civilian injuries and has significant clinical and economic consequences. Despite their vital roles in bleeding management, an optimal topical hemostatic agent (HA) has yet to be developed for a particular scenario. This is partly due to a lack of an overarching quantitative testing technology to characterize the various classes of HAs in vitro. Herein, the feasibility of a novel, contactless, and nondestructive technique to quantitatively measure the shear storage modulus (G') and clotting properties of whole blood in contact with different dosages of eight topical HAs, including particulates and gauze-like and sponge-like systems, was assessed. The real-time G'-time profiles of these blood/HA systems revealed their distinct biomechanical behavior to induce and impact coagulation. These were analyzed to characterize the clot initiation time, clotting rate, clotting time, and apparent stiffness of the formed clots (both immediately and temporally), which were correlated with their reported hemostatic mechanisms of action. Moreover, the HAs that worked independently from the natural blood clotting cascade were identified and quantified through this technology. In sum, this study indicated that the nondestructive nature of the technology may offer a promising tool for accurate, quantitative in vitro measurements of the clotting properties of various classes of HAs, which may be used to better predict their in vivo outcomes.

Concentration dependence of yield stress, thixotropy, and viscoelasticity rheological behavior of lithium-ion battery slurry

The rheological properties of electrode slurry are mainly influenced by the concentration, which further affects the Lithium-ion batteries (LIBs) quality and manufacturing processes. In this work, various methods including steady-state shear, creep, rheological model fitting, hysteresis loop, and small amplitude oscillatory shear (SAOS) measurement were employed to investigate the concentration-dependent rheological behaviors of slurry, in particular its yield stress, thixotropy, and viscoelasticity. Results show that the difference in yield stress obtained from varying methods is observed, in which the yield stresses measured by the SAOS test are closer to the steady-state value due to its advantage that non-destructive property at small deformations only causes minimum disturbance. The improvement of slurry concentration enhances the bonding strength between particles, thereby resulting in an increase of yield stress and thixotropy, and a decrease of the time scale of transient behavior during the creep process. In oscillatory shear measurement, both storage and loss modulus are concentration-dependent, while yielding and strain stiffening corresponding to critical strains exhibit concentration-independent. In addition, the increase in concentration leads to a more pronounced strain stiffening behavior and a lower characteristic frequency as well as a longer relaxation time. Understanding the relationship between concentration and rheological behaviors will be helpful for material design, preparation, and production in different stages.

Effect of Process and Formulation Variables on the Structural and Physical Properties in Cream Cheese using GDL Acidulant

We report on the properties of analogue cream cheeses prepared using glucono delta-lactone (GDL) acidulant, notably the impact of particular processing and formulation variables, (homogenisation pressure, coagulation pH and temperature, and stabiliser level) on cream cheese physical, material and microstructural properties. Protein–protein and protein-fat interactions were seen to be the primary structural contributors to the physical properties of cream cheese. Cream cheese microstructure and its properties demonstrated well-defined correlations to specific and controllable processing elements within the manufacturing process, showing significance in interactions between parameters in multivariable linear regression analysis (P < 0.05). Summarising the effect of processing variables on key cheese properties, we observed that a progressive reduction in fat particle size of cheese milk arising from increasing homogenisation pressures was seen to increase the total surface area of fat that could be incorporated into the curd during coagulation. The greater extent of fat-fat and fat-proteins interactions during coagulation provided a reinforcing effect on the microstructure of the final cream cheese, with a corresponding increase in compressive fracture stress, shear storage modulus (G′) and shear loss modulus (G″). In terms of other processing variables, cream cheese firmness was also observed to progressively increase through lowering of coagulation pH from 5.13 to 4.33. Increasing coagulation temperature from 58 °C to 78 °C similarly caused an increase in cheese firmness. Finally, increasing the levels of added stabiliser were shown to correlate with increasing cheese firmness. Similar correlations could be observed in relation to physical properties, notably forced expressible serum separation. This model cream cheese preparation method has provided a useful model system for relating food structure to material and functional properties. In addition, it has the advantage of being able to rapidly screen many formulation and process variables because it is faster than the traditional cheesemaking. This study showed that the adjustment of process and formulation variables, either in isolation or in combination, in the manufacture of cream cheese can significantly influence the final material and textural properties of the product, thereby enabling controllable functional attributes capable of meeting different customer needs.