Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Book Part Citation - WoS: 12Linear and Non-Linear Rheological Properties of Foods(Taylor & Francis, 2019) Duvarcı, Özlem; Doğan, Hülya; Yazar, Gamze; Çağlar Duvarcı, Özlem; Doğan, Hülya; Kokini, Jozef L.[No abstract available]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: 27Citation - Scopus: 29Non-Linear Rheological Properties of Soft Wheat Flour Dough at Different Stages of Farinograph Mixing(Kerschensteiner Verlag GmbH, 2016) Yazar, Gamze; Duvarcı, Özlem; Tavman, Şebnem; Kokini, Jozef L.During mixing of wheat flour doughs, the distribution of the gluten network changes as a result of continuously applied large deformations. Especially gliadin, changes its distribution in the whole network during mixing. It is possible to fundamentally explain the role of molecular changes in more detail using large amplitude oscillatory measurements (LAOS) in the non-linear region. Therefore, the purpose of this study is to understand the effect of mixing on the non-linear fundamental rheological behavior of soft wheat flour dough using LAOS. Dough samples were obtained at 4 different phases of the Farinograph mixing and LAOS tests were done on each of them. LAOS tets give in depth intracycle understanding of rheology. All samples showed strain stiffening S and shear thinning T behavior at large strains previously not known in the cereal rheology community. Increasing mixing time (phase 1 to phase 4) and decreasing frequency resulted in retardation in the break of strain stiffening as strain increases. The strain stiffening behavior started to decrease for the dough samples at the 3rd and the 4th phases of mixing. LAOS data enabled us to describe the non-linear rheological changes occurring both in the viscous part largely attributed to the starch matrix and elastic part largely attributed to the gluten network components of the soft wheat flour dough under large deformations.