Shear-thinning Flow Research Articles

Coenzyme Q10-loaded nanoemulsion hydrophilic gel: Development, characterization, stability evaluation and in vivo effects in skin

This study aimed to develop a physically and chemically stable hydrogel, which contains coenzyme Q10 (Q10)-loaded nanoemulsion, able to reduce transepidermal water loss (TEWL) and enhance skin hydration. Q10-loaded nanoemulsion was, after its characterization (particle size, polydispersity index (PDI), oxidation index, pH value, Q10-content, and electron microscopy) incorporated into a carbomer gel. The prepared Q10-loaded nanoemulsion gel was analyzed for its rheological parameters, pH value and Q10-content, after its preparation (48 h), after the stress test (5 cycles; 1 cycle: 24 h at 4 °C, 24 h at 20±2 °C and 24 h at 40 °C) and at predetermined time intervals during its storage at 20±2 °C and at 40 °C for six months. The Q10-loaded nanoemulsion gel, plain Q10-gel, Q10-free nanoemulsion gel and placebo carbomer gel were investigated in vivo for their effects in 15 human volunteers, during their 28 days’ application onto the skin. Skin hydration and TEWL were determined before starting the treatment, during 28 days of treatment, and 4 days after treatment completion. The results showed that the Q10-nanoemulsion was of a sufficiently low particle size (307,4 ± 0,5 nm) and homogeneity (PDI = 0.270 ± 0.002) for skin application, and that its characteristics were not changed by its incorporation into the gel. A shear-thinning plastic flow behavior was seen for the Q10-nanoemulsion gel. The stress test as well as storage at 20±2 °C and 40 °C did not change the rheological parameters of the gel. However, Q10-content decreased in the Q10-loaded nanoemulsion gel, but less compared to the Q10-gel. The developed Q10-nanoemulsion gel was able to significantly decrease TEWL compared to untreated skin (control), while it was not able, without the addition of a moisturizing agent (hyaluronic acid) and emollient (C12-15 alkyl benzoate) to increase skin hydration compared to control. Thus, besides the addition of a Q10-nanoemulsion into a hydrogel, it is necessary to add moisturizers and/or emollients to increase skin hydration.

Numerical Investigation on the Conical Flow of Viscoelastic Fluids

The conical problem represents one of the important problems in the various fields of industrial as the automotive industry and the aerospace industry, due to their great role in controlling the flow of liquids and gases. This article covers a computational investigation of incompressible the Phan–Thien/Tanner shear-thinning viscoelastic fluid flow through a conical converging channel. Here, we select hybrid finite element/finite volume algorithm as a first time to treat such problem. This method consists of the combination of a Taylor-Galerkin/pressure correction finite element method (TGPC-FEM) and a cell-vertex finite volume approach (CV-FEA) to solve the system of partial differential equations that govern the fluid flow. The TGPC-FEM is employed to the momentum and mass conservation models, while the stress constitutive models are treated by finite volume implementation. The findings of current study are concerned with stress response, deformation rate, and pressure drop under variations in Weissenberg number and EPTT parameters. The effect of shear-thinning behaviour with the EPTT representation is also considered.

Motion of a circular particle in the power-law lid-driven cavity flow

In this paper, the motion of a circular particle in a lid-driven square cavity with the power-law fluid is studied by using the diffuse interface lattice Boltzmann method, and the study mainly considers the effects of the particle's initial position, the power-law index, the Reynolds number, and the particle size. The numerical results show that the circular particle is first in a centrifugal motion under the effect of inertia, and it finally moves steadily on the limit cycle. Furthermore, it is also found that the initial position of the particle has no influence on the limit cycle. For a shear-thinning fluid flow, the limit cycle moves towards the bottom right corner of the square cavity. Moreover, the particle velocity is small, and the period of the particle motion is long. On the other hand, in the case of shear-thickening fluid flow, the limit cycle moves towards the top left corner of the cavity. In addition, the particle velocity is large, and the period of the particle motion is short.With the increase of Reynolds number, the limit cycle moves towards the bottom right corner of the square cavity, which is caused by a strong fluid flow field. Meanwhile, the particle velocity becomes larger, and the period of the particle motion is shorter. With the increase of particle size, the effect of confinement of the cavity boundary becomes significant, and the circular particle is pushed towards the center of the cavity. In this case, the limit cycle shrinks towards the center of the cavity. The circular particle squeezes the secondary vortices, especially when the circular particle is located in the bottom left, bottom right and top left corners. Additionally, the appearance of the circular particle has a significant influence on the position of the primary vortex, which changes periodically near the position of the primary vortex without the particle. It is also observed that the influence of the circular particle becomes more significant as its size increases and the power-law index decreases.

The Influence of Pseudoplastic Flow Behavior on the Slot Die Process in Solid Electrolyte Production

Solid-state batteries (ASSB) are the next generation of batteries for energy storage. An ion-conducting solid replaces the liquid electrolyte. The trend is toward thin, homogeneous solid electrolytes (SE) that replace the liquid electrolyte and separator. At the same time, the use of a lithium metal anode and the reduction of the layer thickness enable higher energy and power densities. SEs should have a high mechanical strength with a certain flexibility. In addition, electrochemical and chemical properties such as good electrical isolator and good ion conductor, as well as low flammability, are essential. This requirement profile for SEs increases the demand for suitable materials and their processing methods.A promising candidate for the production of SE is the slot die process. This process is mainly controlled by three process parameters, i.e. coatings speed, dispense rate and coating gap. Compared to other production methods, this makes it easy to set parameters for targeted coating thicknesses. The process is already used in many production steps, e.g. for electrodes in the conventional lithium ion battery production. This provides a good opportunity to use and adapt this knowledge for SE production.In general, for coating solutions, structurally viscous fluids have well suited properties. The change in flow properties during shear stress can be used to achieve a certain stability between the coating tool and the substrate to avoid defects during coating. It also ensures easy handling of the system after processing and the shape stability of the resulting coatings.Therefore, a promising candidate as base material for SE production is Poly(ethylene oxide) (PEO). In addition to the shear thinning (or pseudoplastic) flow behavior, it also offers many advantages, such as its good availability on the global market, high solubility in solvents such as acetonitrile, and the capability to dissolve conductive salts like the alkali salt Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).The aim of this work is to investigate the influence of the pseudoplastic flow behavior during and after the coating process by varying the molecular weight (Mw) of PEO. Therefore, the coating window is evaluated as a function of material properties MW and solution concentration. From viscosity and surface tension determination, an increase in MW leading to a stronger pseudoplastic flow behavior can be observed. For the coating process, a DoE employing a constant set of the process parameters dispense rate, coating gap and coating speed is used. The produced layers are evaluated based on their coating quality, dry layer thickness and ionic conductivity. For each solution, the obtained coating window is compared to a theoretical film break-up model.This work shows successful production of SE with an ionic conductivity of 10-6 S/cm using different MW. Further, the experimental results are comparable to the theoretical models. Moreover, the experiments show both, a dependency of MW and PEO concentrations. Within one MW, stable coating window becomes smaller with increasing concentration. Similar behavior is observed at a constant concentration with different MW. Due to the change in flow properties, the stable coating window becomes smaller with increasing MW. As a result of these correlations, the produced dry layer thickness varies depending on the use of MW and the associated PEO concentration.

On flow disturbances caused by pressure taps in highly elastic flows around a microfluidic cylinder

The objective of this work is to characterize the onset of laterally asymmetric flow of viscoelastic solutions around a confined microfluidic cylinder, which was encountered in a recent study [Rodrigues et al., J. Non-Newtonian Fluid Mech. 289, 104406 (2020)]. To this end, two non-Newtonian fluids were employed in the same micro-geometry. Two microchannels were studied, both with a cylinder of diameter 75 μm, aspect ratio (channel height over width) of 0.37, and blockage ratio (cylinder diameter over channel width) of 0.28, differing only on the width of the pressure taps, located 500 μm up- and downstream from the respective cylinder face, on opposing walls. The working fluids consist of two poly(ethylene oxide) solutions: an elastic weakly shear-thinning fluid and an elastic shear-thinning fluid. Micro-Particle Image Velocimetry and streak imaging techniques were used to evaluate the flow over a Weissenberg number range 100≤Wi≤500, while maintaining a low Reynolds number, Re < 1. The elastic shear-thinning solution showed laterally asymmetric flow past the cylinder with both pressure tap designs, while with the weakly shear-thinning solution asymmetric flow was only observed with the wider pressure tap intake. In both cases, the fluids preferentially chose the cylinder/wall gap opposing the upstream pressure tap, which was found to influence the flow greatly, seemingly associated with time-dependent flow and possibly the lateral flow asymmetry itself. This work brings to light the necessary compromise between optimal pressure tap design for quality pressure measurements and minimal flow interference, due to the increased susceptibility of elastic microfluidic flows to flow perturbations.

Development of a “Green” Emulsion with a Milk Protein Hydrolysate: An Evaluation of Rheology, Texture, In Vitro Bioactivity, and Safety

Bioactive peptides are promising cosmetic active ingredients that can improve skin health and appearance. They exhibit a broad spectrum of activity, including anti-aging, antioxidant, antimicrobial, and anti-inflammatory effects. The aim of this study was to develop a safe, stable, and efficacious environmentally friendly (“green”) emulsion using a milk protein hydrolysate as a model active ingredient. Potential emulsions were formulated with biodegradable emollients, stabilized with naturally derived mixed emulsifier, and prepared by cold process. They were evaluated for rheological behavior (continuous rotation and oscillation tests), physical stability (dynamic mechanical thermal analysis—DMTA test), and texture profiles, as well as cytotoxic, antioxidant, and antimicrobial effects. Rheological characterization revealed shear-thinning flow behavior with yield point from continuous rotation tests and predominantly elastic character from oscillation (amplitude and frequency sweep) tests, with small structural change detected in the DMTA test. These results implied satisfactory rheological properties and good stability. Texture analysis revealed acceptable spreadability and substantivity of the emulsions. The protein hydrolysate showed antioxidant activity. The developed emulsions showed low antibacterial activity against selected microorganisms, but this was due to the action of preservatives, not peptides. All potential emulsions showed a desirable safety profile. The results obtained provide the basis for the next stage of formulation development, i.e., in vivo efficacy tests.

Traveling wave solutions for a realistic non-Newtonian foam flow model

Due to several environmental and petroleum engineering applications, there is a renewed interest in studying foam flow in porous media, commonly described as shear-thinning non-Newtonian flow. Based on experiments reporting saturation profiles with an unchanging shape displacing through the medium, we investigate the solution of the model describing foam displacement as a traveling wave. For that, we consider a realistic non-Newtonian foam flow model, which successfully described several experimental studies found in the literature. The aimed traveling wave solution is equivalent to the existence of the solution of the corresponding ordinary differential equations connecting initial and injection conditions. We address this problem by proposing a semi-analytical technique for finding such a connection in the phase space using the explicit foam’s apparent viscosity. Our semi-analytical solution is validated with direct numerical simulations and also by comparing it to experimental data from the literature.

Mixed convection of shear-thinning hybrid nanofluid flow across a radiative unsteady cone with suction and slip effect

The present study examines the intricate dynamics of flow velocities, temperature distribution, and concentration profiles within Casson hybrid nanofluids as they traverse an unsteady vertical rotating cone, accounting for suction velocity and slip effects. The investigation dissects shear stress rates and thermal and mass transfer rates, leveraging the computational power of MATLAB's bvp4c method to tackle the problem's high non-linearity. The research extends to explore the interplay of magnetic parameters, radiation parameters, thermophoresis, Brownian motion, and chemical reactions in the context of Casson hybrid nanofluid flow over an unsteady vertical rotating cone. The incorporation of velocity slip effects and suction velocity emerges as a pivotal catalyst, elevating the rates of heat and mass transfer. Notably, the findings reveal a substantial enhancement in tangential and azimuthal skin friction by 52 % and 34 %, respectively, when transitioning from Casson nanofluid to Casson hybrid nanofluid. Most strikingly, the rate of heat transfer experiences a remarkable surge of 125 % when Casson hybrid nanofluid supplants Casson nanofluid. This research opens up exciting possibilities for improving heat and mass transfer in various industrial applications, making it a compelling contribution to the field of fluid dynamics and nanofluid research.

Comparative study on thermo-mechanical, structural and functional properties of pectin extracted from immature wasted apples and commercial pectin

Pectin yield of 22.22 ± 0.98 % (dry basis) was achieved from prematurely dropped Golden Delicious apples, having a light orange hue (hue value: 78.08 ± 0.04) and an overall color difference (ΔE) of 9.92 ± 0.01 compared to commercial pectin (CP). Extracted AP exhibited a lower equivalent weight (725.24 ± 29.73) and higher methoxy content (8.36 ± 0.28 %) in contrast to CP. However, a similar degree of esterification of 71.57 ± 0.79 and 70.55 ± 0.59 %, was observed in AP and CP respectively. Apple pectin demonstrated slight lower galacturonic acid (GalA) content of 68.10 ± 3.94 % in comparison to 72.31 ± 4.62 % of CP, which was further corroborated by reduced intensity in FTIR fingerprint region (912–1025 cm−1). Morphology revealed a sheet-like cloudy appearance indicating a significant presence of associated sugars whereas X-ray diffraction highlighted the highly amorphous nature of AP. AP and CP solutions (3–9 %) displayed a shear-thinning flow and viscoelastic behavior where the loss (G') moduli dominated over the storage moduli (G"). Owing to high degree of esterification, galacturonic acid content (>65 %) that aligns with commercial standards and viscoelastic behavior, the extracted AP holds promise for potential utilization in commercial applications. This study underscores the potential for sustainable utilization of prematurely dropped apples through pectin extraction, contributing to valorization of the wasted bioresource.

Synergistic approach for acne vulgaris treatment using glycerosomes loaded with lincomycin and lauric acid: Formulation, in silico, in vitro, LC-MS/MS skin deposition assay and in vivo evaluation

This study aims to develop a pharmaceutical formulation that combines the potent antibacterial effect of lincomycin and lauric acid against Cutibacterium acnes (C. acnes), a bacterium implicated in acne. The selection of lauric acid was based on an in silico study, which suggested that its interaction with specific protein targets of C. acnes may contribute to its synergistic antibacterial and anti-inflammatory effects. To achieve our aim, glycerosomes were fabricated with the incorporation of lauric acid as a main constituent of glycerosomes vesicular membrane along with cholesterol and phospholipon 90H, while lincomycin was entrapped within the aqueous cavities. Glycerol is expected to enhance the cutaneous absorption of the active moieties via hydrating the skin. Optimization of lincomycin-loaded glycerosomes (LM-GSs) was conducted using a mixed factorial experimental design. The optimized formulation; LM-GS4 composed of equal ratios of cholesterol:phospholipon90H:Lauric acid, demonstrated a size of 490 ± 17.5 nm, entrapment efficiency-values of 90 ± 1.4 % for lincomycin, and97 ± 0.2 % for lauric acid, and a surface charge of −30.2 ± 0.5mV. To facilitate its application on the skin, the optimized formulation was incorporated into a carbopol hydrogel. The formed hydrogel exhibited a pH value of 5.95 ± 0.03 characteristic of pH-balanced skincare and a shear-thinning non-Newtonian pseudoplastic flow. Skin deposition of lincomycin was assessed using an in-house developed and validated LC-MS/MS method employing gradient elution and electrospray ionization detection. Results revealed that LM-GS4 hydrogel exhibited a two-fold increase in skin deposition of lincomycin compared to lincomycin hydrogel, indicating improved skin penetration and sustained release. The synergistic healing effect of LM-GS4 was evidenced by a reduction in inflammation, bacterial load, and improved histopathological changes in an acne mouse model. In conclusion, the proposed formulation demonstrated promising potential as a topical treatment for acne. It effectively enhanced the cutaneous absorption of lincomycin, exhibited favorable physical properties, and synergistic antibacterial and healing effects. This study provides valuable insights for the development of an effective therapeutic approach for acne management.

Unleashing the potential of flash vacuum expansion: an innovative approach for Andean Blackberry (Rubus glaucus Benth) Processing

Andean Blackberry fruits (Rubus glaucus Benth) have promising market potential with notable nutritional and antioxidant properties; however, their limited 3-6day shelf-life presents considerable challenges. A flash vacuum expansion (FVE) process coupled with vacuum de-pulping was used to obtain puree from blackberry fruits. Different steam heating holding times (53, 75, 85, and 95 s) were tested at a pressure of 130 kPa. After FVE and vacuum de-pulping (5kPa), various parameters, including alcohol insoluble residues (AIR), residual activity of polyphenol oxidase (RAPPO), anthocyanins, ascorbic acid and ellagitannin retention, rheological properties, and microbial reduction, were evaluated in the purees. Optimal steam heating time of 85 seconds was selected for the FVE process, showing outstanding retention rates of 98% for cyanidin-3-O-glucoside and 88% for ascorbic acid, along with enhanced ellagitannins extraction from torus and seed blackberries into the puree. The purees displayed a gradual shear-thinning flow behavior, positively correlated with the increase in %AIR. A reduction greater than 5 Log10 CFU / mL was achieved for molds, yeasts, aerobic mesophilic, and coliforms counts for all the treatments. Nectar and sweetened puree products developed from the optimal FVE processed puree, received favorable acceptance from consumers, with a high intention to purchase. The findings demonstrated that this innovative process has great potential for developing of high-quality products.

Influence of particle size on powder flow behaviour, textural and viscoelastic properties of milk-based whippable emulsions

This study focuses on the rheological, textural and powder flow characteristics of whippable oil-in-water emulsion with ingredients of different particle sizes (0.2, 0.5 and 1.0 μm) and compares them with the control sample. Rheological studies confirmed that all samples had shear thinning flow behaviour with higher determination coefficients (R2 >0.995). The smaller particle size further improved the dispersed phases, reducing the mean inter-particle distances. Therefore, the higher apparent viscosity resulted from particles being more difficult to move and inter-particle resistance rising. The adhesiveness tendency of the whippable emulsions decreased with increasing particle size. The highest cohesiveness value was determined in the control whippable emulsion and the lowest value was recorded at whippable emulsions containing 0.2 μm ingredients (0.2WC). This result suggests that whippable emulsion with a higher particle size was not easy to deform and was less crumbly.

Heat transfer characteristics of a Williamson fluid flow through a variable porosity regime

A theoretical framework pertaining to the study of boundary layer flow of a Williamson fluid over a moving vertical cylinder with variable porosity has been discussed. The significance of this analysis is to investigate the heat transfer enhancement for a shear thinning flow over a cylinder entrenched in a variable permeability of the porous medium. Prandtl boundary layer equations with appropriate conditions are solved numerically through the utility of a Crank Nicholson method. The impressions of the various morphological and rheological characteristics involving parameters like variable porosity parameter, Williamson parameter, Nusselt number and Sherwood number have been scrutinized and presented graphically. Low-velocity profile develops for the variable porosity parameter with high intensity. It has been discerned that the ferocity of heat and mass transfer rates is high, when there is less variation supervenes in the shear-thinning fluids. Moreover, the velocity boundary layer will override the thermal boundary layer for a substantial increase in the Prandtl number. Further, the validation of the results was verified through an extensive comparative study with the available results in the literature.

Proteomic Identification and Characterization of Collagen from Bactrian Camel (Camelus bactrianus) Hoof.

With the development of camel-derived food and pharmaceutical cosmetics, camel hoof, as a unique by-product of the camel industry, has gradually attracted the attention of scientific researchers in the fields of nutrition, health care, and biomaterial development. In this study, the protein composition and collagen type of Bactrian camel hoof collagen extract (CHC) were analyzed by LC-MS/MS, and the functional properties of CHC were further investigated, including its rheological characteristics, emulsification and emulsion stability, and hygroscopicity and humectancy. Proteomic identification confirmed that CHC had 13 collagen subunits, dominated by type I collagen (α1, α2), with molecular weights mainly in the 100-200 KDa range and a pI of 7.48. An amino acid study of CHC revealed that it carried the standard amino acid profile of type I collagen and was abundant in Gly, Pro, Glu, Ala, and Arg. Additionally, studies using circular dichroism spectroscopy and Fourier transform infrared spectroscopy revealed that CHC contains a collagen-like triple helix structure that is stable and intact. Different concentrations of CHC solutions showed shear-thinning flow behavior. Its tan δ did not differ much with increasing concentration. The CHC has good emulsifying ability and stability, humectancy, and hygroscopicity. This study provides a basis for utilizing and developing Bactrian camel hoof collagen as a functional ingredient.

Rheological and functional characteristics of starch and flour on different drying methods from Beneng Taro as sustainability products from agricultural in Banten

Beneng Taro is a type of taro found in Banten agricultural but has not been appropriately utilized. The drying process is critical since temperature changes will result in various properties. This research aimed to evaluate the rheology and functional characteristics of starch and flour made from Beneng Taro dried in the sunlight and hot air as sustainability products of it. This research contains the extraction of starch, the production of flour, and characterizing the starch and flour produced. The rheological characteristics of the flour and starch from the can be model using the Herschel-Bulkley. Starch and flour showed non-Newtonian shear-thinning flow characteristics, according to the flow behavior index. The difference in the consistency index value of flour is significant, where flour dried with sunlight shows a higher value. Both starch and flour show a sharp decrease in viscosity at low shear rates. The value of the starch and flour’s swelling power shown that cabinet drying was superior to drying outdoors in the sun. The solubility index undergoes the same phenomenon. In contrast to water and oil holding capacity, sun drying shows a higher value. Knowing the characteristics of the starch and flour produced can be applied as a food source.

Development and Characterization of Anticancer Model Drug Conjugated to Biosynthesized Zinc Oxide Nanoparticles Loaded into Different Topical Skin Formulations

Doxorubicin (DOX) is an anthracycline antineoplastic agents, which interacts with DNA and shows sever toxicity due to its lack of specificity. The cytotoxic effect of zinc oxide nanoparticles (ZnO NPs) is mainly concerned in changing the cytoskeleton and nucleoskeleton of proteins and/or producing reactive oxygen species (ROS) in cells exposed to ZnO NPs. The green synthesis of ZnO NPs from plant extracts has been recently employed as a simple, eco-friendly, safe, and cost- and time-effective approach with higher stability and reproducibility. Phoenix dactylifera, due to its chemical component (tannins, phenolic acid, and carotenoids), was employed in the preparation of ZnO NPs. The main objective of this study is to greenly synthesize ZnO NPs conjugated with DOX (DOX-ZnO NPS) and loaded into various types of gel preparations (hydrogel and oleogel). P.dactylifera solution extract was mixed with 0.6M zinc acetate at 1:1 v/v ratio to prepare ZnO NPs. The prepared NPs was characterized by UV-vis spectroscopy, particles size, PDI, and zeta potential. The maximum wavelength of ZnO NPs was detected at 360 nm. Dialysis method was used to determine the effect of ZnO NPs on enhancing DOX release. The cumulative amount of DOX was calculated via UV-vis spectroscopy at 480 nm after 48 h. Spherical nanoparticles of size range 15.35–28.74 nm and -22mV zeta potential was obtained. The rheological results showed that both gel formulations exhibited a pseudoplastic (shear-thinning) flow and viscoelastic behavior. The in vitro release studies showed that ZnO NPs enhanced the release of DOX, where the amount of DOX released from DOX-ZnO NPs hydrogel and oloegel was higher than that of DOX-hydrogel and oleogel. In addition, DOX-ZnO NPs hydrogel showed a faster release that DOX-ZnO NPs oleogel. Therefore, an eco-friendly and low-cost greenly synthesized ZnO NPs were successfully developed, conjugated with DOX, and loaded into hydrogels and oleogels for dermal delivery.

Valorization of Soybean Residue (Okara) by Supercritical Carbon Dioxide Extraction: Compositional, Physicochemical, and Functional Properties of Oil and Defatted Powder.

In the context of food waste valorization, the purpose of this study is to demonstrate the complete valorization of soybean residue (okara) through supercritical carbon dioxide extraction (SCE). Okara oil (OKO) was separated from full-fat powder (FFP) using SCE with and without ethanol (EtOH) as a cosolvent. The kinetics of extraction, chemical composition, and physicochemical, functional, and health-promoting properties of OKO and defatted powder (DFP) were determined. The process yielded 18.5% oil after 450 min. The soluble dietary fiber and protein of the DFP increased significantly; its water and oil absorption capacities increased despite the decrease in swelling capacity corresponding to particle size reduction. The OKO was rich in linoleic and oleic acids, with a ratio of ω6-to-ω3 fatty acids = 9.53, and EtOH increased its phenolic content (0.45 mg GAE/g), aglycone content (239.6 μg/g), and antioxidant capacity (0.195 mg TE/g). The DFP paste showed gel-like consistency and shear-thinning flow behavior, whereas the OKO showed characteristic transition of the product and affected lubrication at contact zones. Both fractions showed potential as food ingredients based on their nutritional and functional properties, as well as the capability of modifying the microstructure of a model food system.

Investigation on the Flow Behaviour of Agar Solution and Rheological Modelling

In this study, the effect of shear rate, agar concentration (15-35 kg/m3) and temperature (30-60°C) on the apparent viscosity of the agar solution was investigated. Apparent viscosities at different shear rates were determined using a rotational viscometer. The findings show that the apparent viscosity decreasing with a rise of shear rate increased with increasing concentration. An increase in the tempearture, on the other hand, led to a decrease in the apparent viscosity. To illustrate both temperature and concentration changes together, the Bingham, power law, and Casson models were utilized in choosing the most suitable model. When the models were compared using statistical tests, the most compatible model was found to be the power-law model. The consistency coefficient and flow behaviour index calculated using the power law model showed that agar solutions exhibited shear-thinning flow behavior (pseudoplastic). This study suggests that power law, within the ranges of the temperature and concentration studied could be used to estimate the viscosity of the agar solutions in the applications requiring the knowledge of flow behavior.

Predicting Shear-Thinning Fluid Flows in Porous Media Using Pore Network Modeling: Simulations and Experimental Validation

Predicting Shear-Thinning Fluid Flows in Porous Media Using Pore Network Modeling: Simulations and Experimental Validation

OBSERVATION OF THE SUITABILITY OF SINGLE STRAINS OF STREPTOCOCCUS THERMOPHILUS AND LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS ISOLATED FROM LOCAL DAIRY SOURCES IN TURKEY AS YOGURT STARTER COMBINATIONS

The present study investigated the suitability of combinations one Streptococcus thermophilus and five Lactobacillus delbrueckii subsp. bulgaricus isolates for industrial yogurt productions. The isolates were selected after a detailed pre-screening procedure based on acidification performances, production of volatile aroma compounds, texture developing properties and sensory evaluations of yogurts made from single cultures. The fermentation profiles of the combinations were investigated by monitoring the small oscillatory rheological parameters and pH reductions during fermentation. The variations in some physical, chemical and organoleptic characteristics of the yogurt samples were also monitored during cold storage at 4 ºC for 21 days. Results indicated that all the combinations reduced the milk acidity to pH 4.6 within 4-5 hour at 43 ºC. Gelation profiles of the samples were close to each other (close tan δ values) with different elastic (G') and loss (G") moduli, indicating that similar chemical bondings took place in gel formation with different levels. All the samples showed a shear-thinning non-Newtonian flow behavior. Total number of starter bacteria was higher than 6 log cfu/mL in each sample after 21 days of storage. The post-acidification rates were also limited (between 4.21-4.37 after 21 days of cold storage). Untrained sensory evaluation panel found no marginal differences between the samples regarding appearance, body and texture, and aroma and flavor of the samples. To conclude, the combinations examined in this study were found to be suitable for commercial yogurt productions.