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    Öğe
    Dynamic rheological characterization of salep glucomannan/galactomannan-based milk beverages
    (Elsevier Sci Ltd, 2009) Yasar, Kurban; Kahyaoglu, Talip; Sahan, Nuray
    The steady flow and viscoelastic properties of glucomannan (salep) and galactomannans (locust bean gum, LBG and guar gum, GG) in milk beverages were investigated at 25 and 50 degrees C. The consistency index (K), flow behavior index (n), yield stress and thixotropic area were measured as functions of steady shear; elastic modulus (G'), loss modulus (G ''), tan delta and complex viscosity (eta*) parameters were derived from oscillatory shear experiments. The steady flow behavior of mannan-based milk beverages was observed to be shear-thinning and thixotropic. Galactomannans exhibited greater shear-thinning and thixotropy than glucomannan in milk beverages. The synergistic effect was detected between salep and LBG with highest thixotropy. Increasing the temperature decreased Casson yield stresses of GG but not salep and LBG samples. Similar viscoelastic behavior was observed between salep and LBG, they could be classified as concentrated solutions but GG showed gel-like structure. At low frequencies, high tan delta values were observed for the salep and LBG samples indicating viscous character. On the other hand, GG sample had nearly the same tan delta values through the frequency sweep. Cox-Merz rule was tested to correlate the steady and dynamic viscosities of samples. It was found that Cox-Merz rule was applicable only to LBG-milk beverage among the studied samples. (C) 2008 Elsevier Ltd. All rights reserved.
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    Öğe
    The effects of using exopolysaccharide producing cultures on the microbiological, physicochemical and sensory properties of ayran
    (M H Schaper Gmbh Co Kg, 2006) Sahan, Nuray; Var, Isil; Yasar, Kurban; Zorlugenc, Buelent
    In this study, the microbial properties of ayran made from different starter cultures were investigated during refrigerated storage for 1, 8 or 15 days. Microbiological, physicochemical and also sensory properties of ayran were examined. It was determined that the different starter cultures had a significant effect on the numbers of lactic acid bacteria (p < 0.05),total aerobic mesophilic bacteria (p < 0.05) and yeast counts (p < 0.01). The storage time had a significant effect on the lactic acid bacteria (p < 0.05). The use of various starter cultures significantly influenced acetaldehyde contents (p < 0.05), viscosity (p < 0.01), whey separation (p < 0.01), appearance (p < 0.05) as well as body and texture (p < 0.01). The storage time affected volatile fatty acids (p < 0.01), whey separation (p < 0.01) and appearance (p < 0.01). Addition of exopolysaccharide producing cultures decreased whey separation and caused an increase in viscosity and sensory scores in ayran samples. It is recommended that precautions should be taken to decrease whey separation to prevent the negative effect of storage time.