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    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 functional, rheological and sensory characteristics of ice creams with various fat replacers
    (Wiley, 2009) Karaca, Oya Berkay; Guven, Mehmet; Yasar, Kurban; Kaya, Sevim; Kahyaoglu, Talip
    The effects of fat replacers (Simplesse (R) D-100, N-Lite D, and inulin) on the melting characteristics, overruns, hardness, rheological parameters and sensory attributes of reduced (RF, 60.0 g/kg), low (LF, 40.0 g/kg), and nonfat (NF, 1.0 g/kg) ice creams were investigated. The magnitudes of the melting rates were in the order RF > LF > NF for samples that contained Simplesse (R) D-100 or inulin, but the reverse order was found for samples with N-Lite D. The nonfat ice creams had lowest overrun values of around 10%. Inulin-containing ice creams possessed higher overrun values than others (P > 0.05). The use of fat replacer decreased the hardness of ice creams. All ice cream samples showed pseudoplastic (shear-thinning) behavior. The addition of N-Lite D and inulin decreased the flow behaviour index of ice cream samples. The reduced and low fat ice cream samples were rated as similar to the control by a sensory panel. On the other hand, no correlations (P > 0.05) were observed between rheological parameters and sensory texture and mouthfeel.