15C-18 |
Viscoelastic properties of composite gels consisting of fractionated whey proteins and fractionated milkfat |
Y. MOR-ROSENBERG, M. Rosenberg, and C. F. Shoemaker. Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616 The composite nature of emulsion gels suggests that their viscoelastic properties are affected, among other things, by proportions, composition and physico-chemical properties of matrix and filler constituents. Viscoelastic properties of emulsion gels consisting of fractionated whey proteins and selected fractions of milkfat were investigated. Emulsion gels (13% matrix protein; 10 or 30% filler phase) and matrix only gels (13% protein) were prepared at 90°C. The ratio of a-lac - to- b-lg in the protein matrix ranged from 0:100 to 100:0. Filler phase consisted of AMF (M.P. 38°c) or one of its fractions VLM, MM2, HM1 and VHM (M.P.13, 29, 40 and 50°C, respectively). Frequency sweep tests (0.1-10Hz) were performed on gels cylinders (18mmDX10mmL) at 4, 25 and 50°C, using a parallel-plate controlled-stress rheometer. Effects of composition variables and temperature on complex shear modulus (G*), storage modulus (G'), loss modulus (G") and tan (d) were investigated. In all cases, G' values of gels were significantly higher than G" values, indicating the solid-like nature of the composite. Moduli of the gels were inversely proportional to test temperature, were significantly affected by matrix and filler composition and by the matrix-to-filler components ratio. Effect of temperature could be attributed to its effect on matrix properties and on the solid-to-liquid ratio in filler lipids. Manifestation of elastic properties was proportionally related to b-Lg proportion in the matrix and to the solid (crystalline) lipid content in the filler. a-Lac-only and b-Lg-only gels exhibited the highest and lowest tan d values, respectively, indicating a more viscous nature for the a-Lac-rich gels and higher elasticity of the b-Lg-rich-gels. Results indicated significant opportunities in modulating the viscoelastic properties of the composite gels. This may provide new applications for fractionated whey proteins and fractionated milkfat in tailoring rheological properties of composite gels consisting of milk-derived components.
Session 15C, Dairy Foods
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