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S. TIZIANI and Y. Vodovotz. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007 The potential health benefits of soy products and tomatoes, attributed in part to the presence of isoflavones and carotenoids, have been associated with a reduced risk of several cancers and heart disease. The development of highly acceptable novel foods containing various ingredients with potential health-promoting compounds is in great demand. Our objective was to characterize the rheological behavior of three products: plain tomato juice (TJ), tomato juice with 1% soy protein (TJSP) and tomato juice with addition of 1.5% soy germ (TJSG). Steady and dynamic rheological experiments were performed using a controlled rate RFS II Rheometrics system with Couette geometry at 25°C. Effects of temperature on viscosity were studied by dynamic frequency experiments at different temperatures and by dynamic temperature ramps. Shear thinning behavior was observed for all tomato juice products. The time dependence of TJ and TJSG depicted a thixotropic behavior. Addition of soy protein resulted in a thixotropic behavior at low shear rates with a transition to rheopectic behavior at higher shear rates. Dynamic tests indicate a weak physical gel behavior for all the samples; however, an increased gel strength and water holding capacity was observed upon addition of soy products to the tomato juice. The viscosity of TJ and TJSG did not follow Arrhenius kinetics when examined at different temperatures, while for TJSP, the viscosity decreased with increasing temperature. Rheological measurements suggest the addition of soy ingredients increased viscosity preventing separation between serum and particles, thereby improving the product’s stability. Conformational changes of the soy protein, when subjected to different shear rates, were hypothesized to influence the colloidal interactions with tomato particles and reinforce the network structure and the stability of the overall tomato system.
Session 94, Food Chemistry: Chemical effects of food processing, preservation and formulation
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