Rheological properties of skim milk gels at various temperatures; interrelation between the dynamic moduli and the relaxation modulus |
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Authors: | P Zoon S P F M Roefs B de Cindio T van Vliet |
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Institution: | (1) Department of Food Science, Wageningen Agricultural University, The Netherlands;(2) NIZO, P.O.Box 20, 6710 BA Ede, The Netherlands;(3) Dipartimento di Ingegneria Chimica, University of Naples, Italy |
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Abstract: | The rheological properties of rennet-induced skim milk gels were determined by two methods, i.e., via stress relaxation and dynamic tests. The stress relaxation modulusG
c
(t) was calculated from the dynamic moduliG andG by using a simple approximation formula and by means of a more complex procedure, via calculation of the relaxation spectrum. Either calculation method gave the same results forG
c
(t). The magnitude of the relaxation modulus obtained from the stress relaxation experiments was 10% to 20% lower than that calculated from the dynamic tests.Rennet-induced skim milk gels did not show an equilibrium modulus. An increase in temperature in the range from 20° to 35 °C resulted in lower moduli at a given time scale and faster relaxation. Dynamic measurements were also performed on acid-induced skim milk gels at various temperatures andG
c
(t) was calculated. The moduli of the acid-induced gels were higher than those of the rennet-induced gels and a kind of permanent network seemed to exist, also at higher temperatures.
G
storage shear modulus,N·m–2;
-
G
loss shear modulus,N·m–2;
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G
c
calculated storage shear modulus,N·m–2;
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G
c
calculated loss shear modulus,N·m–2;
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G
e
equilibrium shear modulus,N·m–2;
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G
ec
calculated equilibrium shear modulus,N·m–2;
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G(t)
relaxation shear modulus,N·m–2;
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G
c
(t)
calculated relaxation shear modulus,N·m–2;
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G
*(t)
pseudo relaxation shear modulus,N·m–2;
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H
relaxation spectrum,N·m–2;
-
t
time,s;
-
relaxation time,s;
-
angular frequency, rad·s–1.
Partly presented at the Conference on Rheology of Food, Pharmaceutical and Biological Materials, Warwick, UK, September 13–15, 1989 33]. |
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Keywords: | Milkgels rheology stressrelaxation dynamicmoduli temperature |
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