Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Book Part Citation - WoS: 28Citation - Scopus: 26Laos (large Amplitude Oscillatory Shear) Applications for Semisolid Foods(Springer, 2019) Yazar, Gamze; Çağlar Duvarcı, Özlem; Yıldırım Ertürk, Merve; Kokini, Josef L.The rheological behavior of semisolid foods under large amplitude oscillatory shear (LAOS) can offer more detailed understanding of structural changes occurring during processing and consumption compared to traditional rheometry. This chapter focuses on a detailed description of LAOS measurements, including theory, testing method, data interpretation, and corrections. It also discusses LAOS application to food systems with different core structures ranging from dilute dispersions to gels, foams, emulsions, and soft elastic networks, along with a special emphasis on yogurt. Type of stress responses for different rheological behavior, Lissajous-Bowditch curves, and the resulting LAOS parameters e3/e1, ?3/?1, S, and T) are used to understand the structural changes in all of these foods with special emphasis on high-fat, low-fat, and non-fat yogurt. © 2019, Springer Nature Switzerland AG.Article Citation - WoS: 63Citation - Scopus: 70Laos Behavior of the Two Main Gluten Fractions: Gliadin and Glutenin(Elsevier Ltd., 2017) Yazar, Gamze; Çağlar Duvarcı, Özlem; Tavman, Şebnem; Kokini, Jozef L.Crude gliadin and glutenin fractions were studied using Large Amplitude Oscillatory measurements. LAOS measurements were carried out at three different frequencies (20, 10, 1 rad/sec) between the strain values of 0.01–200%. The beginning of non-linearity for glutenin occurred at ∼2.5%, while an initial region of strain hardening was observed for gliadin (2.5–10%) at 1 rad/sec frequency and up to 15% at the higher frequencies applied. Lissajous curves showed in the elastic analysis of both fractions glutenin was more elastically dominated since Lissajous curves were narrower, while for gliadin the ellipses were much broader suggesting more fluid-like behavior and each ellipse depended on the magnitude of frequency. Decreasing frequency increased the viscous behavior of both glutenin and gliadin in the non-linear region, but the change in gliadin was much more pronounced. Gliadin molecules only display intramolecular disulfide bonds creating a great deal of mobility whereas for glutenin molecules, which contain both intermolecular and intramolecular disulfide bonds, the strong network structure formed by this molecular arrangement results in very pronounced strain stiffening.Article Citation - WoS: 42Citation - Scopus: 45The Saos, Maos and Laos Behavior of a Concentrated Suspension of Tomato Paste and Its Prediction Using the Bird-Carreau (saos) and Giesekus Models (maos-Laos)(Elsevier Ltd., 2017) Çağlar Duvarcı, Özlem; Yazar, Gamze; Kokini, Jozef L.The SAOS and LAOS behavior of tomato paste were investigated in this study. SAOS rheology was well predicted by the semi-empirical Bird-Carreau constitutive model. The LAOS (Large amplitude oscillatory shear) behavior of tomato paste was also investigated in depth in this study and non-linear rheological properties were obtained by utilizing Ewoldt-McKinley theory. These parameters offer new insights into the rheology of tomato paste and help understand structural changes which occur at different deformations (strain) and time scales (frequency). We plotted the intracycle normalized stress vs. normalized strain in the linear and non-linear regions offered new intracycle insights and observations. Tomato paste showed an irreversible structural change in LAOS evidenced by strain softening (in the mid-oscillatory region) followed by strain hardening (in the large oscillatory region). The nonlinear flow behavior simulated by the single mode Giesekus model gave good results up to moderate strains and frequencies. These results help gain better insights at large deformations, which occur during processing and consumption.Article Citation - WoS: 41Citation - Scopus: 42Non-Linear Rheological Behavior of Gluten-Free Flour Doughs and Correlations of Laos Parameters With Gluten-Free Bread Properties(Elsevier Ltd., 2017) Yazar, Gamze; Çağlar Duvarcı, Özlem; Tavman, Şebnem; Kokini, Jozef L.Predicting loaf volume development of gluten free baked products to have similar properties to wheat products remains a challenge and there is no good marker for loaf volume. Large Amplitude Oscillatory Shear (LAOS) flow experiments and baking tests were conducted on rice, buckwheat, quinoa, and soy flour doughs to understand if there is any correlation between the non-linear rheological properties and loaf volume. The challenging water absorption capacities were determined by matching the η* vs. frequency data of the gluten free flours with that of the soft wheat flour dough with moisture content at 500 BU. 110%, 90%, 85%, and 160% water levels were found as optimal for rice, buckwheat, quinoa, and soy flour, respectively. The comparison of elastic Lissajous-Bowditch curves showed that the stronger non-linearities were seen at low frequencies and the wider the loop, the weaker the structure and the more structural breakdown with an order of soft wheat, soy, buckwheat, quinoa and rice flour doughs. Secondary loops have been observed in viscous Lissajous-Bowditch curves which are related to the strong non-linearities in elastic stress. The distributions of elastic and viscous LAOS parameters showed that soy dough has the closest rheological performance to wheat dough among other dough samples, which has the highest protein content. GL ′ and GM ′ values at 10 rad/s and 200% strain showed the best correlation among all LAOS parameters with the loaf volume. The strain stiffening/softening property e3/e1 complemented the mechanistic explanations which were offered using GL ′ and GM ′ values.Article Citation - WoS: 54Citation - Scopus: 58Effect of Mixing on Laos Properties of Hard Wheat Flour Dough(Elsevier Ltd., 2016) Yazar, Gamze; Çağlar Duvarcı, Özlem; Tavman, Şebnem; Kokini, Jozef L.Large Amplitude Oscillatory Shear (LAOS) tests were conducted at strains ranging from 0.01% to 200% and different frequencies (20, 10, 1, and 0.1 rad/sec) on hard wheat flour dough samples obtained from the different phases of Farinograph mixing: 1) at the first peak, 2) 5 min after the first peak, 3) 12 min after the first peak, 4) at the 20th min. All samples showed strain stiffening and shear thinning behavior in large strains. The gluten network is the origin of strain stiffening behavior and the rearrangement of the suspended starch matrix is the origin of shear thinning behavior. LAOS enables us to independently deconvolute these two events offering new insights into the structural origins of rheological properties in the non-linear region. Dough samples started to show strain softening and shear thickening after giving a peak around 100% strain due to the onset of the breakdown of the gluten network.Article Citation - WoS: 19Citation - Scopus: 17Preparation and Characterization of Nanocrystalline Titania Powders by Sonochemical Synthesis(Elsevier Ltd., 2012) Çağlar Duvarcı, Özlem; Çiftçioğlu, MuhsinNanocrystalline mesoporous titania powders were synthesized by hydrolyzing titanium isopropoxide in ethanol-water mixtures which were ultrasonically treated without using any templates or chemicals. Titanium isopropoxide-ethanol mixture was added dropwise to a water-ethanol mixture placed in an ultrasonic bath. The properties of the sonochemically synthesized powder were compared with those of the powders prepared without ultrasonic treatment along with Degussa P-25 titania powder. The phase structure, crystallite size, surface area, particle size, powder density were determined and sintering behavior was analyzed in this work. The nanotitania powder prepared during ultrasonic induced hydrolysis (TiO 2-U) was determined to be formed from a mixture of anatase and brookite phases at 25°C. The brookite phase in nanotitania powder prepared without ultrasonic treatment (TiO 2-NoU) was detected at 70°C. The anatase-rutile phase transformation was completed in the 500-700°C range for both powders. The average crystallite sizes of the powders at 25°C were determined as 10 and 5nm for TiO 2-NoU and TiO 2-U, respectively. The surface area decreased from 238 to106m 2/g for TiO 2-NoU and from 287 to 82m 2/g for TiO 2-U when the calcination temperature was increased from 200 to 500°C. The evolution of the N 2 adsorption-desorption behavior with calcination temperature and the corresponding pore size distributions/volumes was attributed to the formation of closely packed submicron aggregates during powder synthesis and calcination. The sintering behavior was concluded to be controlled by 7-10nm crystallites and the submicron aggregates. The determination of the densification behavior of titania powders prepared by different methods with various levels of dopants may prove to be very useful for a better understanding of the phase/pore structure evolution which is crucial for a significant number of applications.Article Citation - WoS: 44Citation - Scopus: 50Thermal Behaviour of a Zeolitic Tuff(Elsevier Ltd., 2007) Çağlar Duvarcı, Özlem; Akdeniz, Yelda; Özmıhçı Ömürlü, Filiz; Ülkü, Semra; Balköse, Devrim; Çiftçioğlu, MuhsinNatural zeolites undergo structural changes after heating which open their possible use in different fields, related to their chemical and physical properties, such as building stone, lightweight aggregate, ceramic foam, concrete bricks, tiles, porcelain stoneware and additive in puzzolonic cements. In this study, thermal behavior of zeolitic tuff quarried from Gördes-Manisa, region of Turkey was investigated. Zeolitic rocks were first reduced to 2 μm and pellets were prepared by dry-pressing. The pellets were heated for 30 min in the temperature range of 200-1200 °C. Heating the tuff up to 600 °C did not cause any structural change detectable by X-Ray powder diffraction (X-Ray), Fourier Transform Infrared Spectroscopy (FTIR) and thermal characterization methods with regard to the original sample, while further increase in the temperature caused structural breakdown of zeolitic tuff. The appearance of the broad low intensity peaks in X-Ray diffraction diagrams indicated most probably a partial transformation of crystal structure into an amorphous structure. The Scanning Electron Microscopy (SEM) micrographs showed that the crystals seen in the original rock sample were broken during grinding and pressing processes. The crystal structure disappeared above 1000 °C and the spherical pores was observed at 1200 °C. Chemical composition of the zeolitic tuff did not change significantly with respect to temperature. The highest density (2.28 g/cm3) and hardness (387 Hv) were obtained by sintering the pellets at 1000 °C for 30 min.Conference Object Citation - WoS: 5Citation - Scopus: 5Preparation and Microstuructural Development of Nanocrystalline Titania and Alumina(Trans Tech Publications, 2004) Çağlar Duvarcı, Özlem; Çiftçioğlu, Muhsin; Güden, Mustafa; Arıkut, G.The preparation of nanocrystalline titania and alumina was investigated by sol-gel methods using titanium isopropoxide, boehmite and aluminum isopropoxide. Various drying control chemical additives like oxalic acid, acetic acid and polyacrylic acid were used for modifying the drying behaviour and shrinkage of the gels. The sintered densities of the ceramics prepared by sol-gel processing and the dried gels were in the 79-99% of theoretical density for rutile. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation techniques for titania were in the 40-52% and 55-83% respectively. The titania ceramics were observed to experience anatase-rutile phase transformation upon heat treatment at 650oC. The grain size of the sintered ceramics at 650oC was determined to be about 26 nm. Grain size of titania increased to 213 nm. at 850oC. The mechanical properties of these nanocrystalline ceramics were investigated by using microhardness testing.