Influence of storing time and temperature on the viscosity of an egg yolk

The influence of storing time and temperature on rheological behavior of egg yolk was investigated. The eggs of two brown egg-laying breeds (Bar Plymouth Rock and Rhode Island Red) were stored for 1, 2, 3, 4, and 8 weeks at constant temperatures: 4 °C, 8 °C, 12 °C, and 16 °C. The apparent viscosity was measured by a rotational viscometer as a function of shear rate. It was found that yolk samples exhibited shear-thinning (pseudoplastic) behavior. The shear-thinning behavior was fitted well into Herschel–Bulkley model (with a satisfying correlation of R2 > 0.95). For the selected shearing rate, viscosity was measured in relation to shearing time. The time-dependant viscosity decreased rapidly with time and, at lower share rates, reached an equilibrium state. The time-dependant viscosity was also found to decrease with storage time. The value of pH changed (increased) during storing. No clear dependence between pH value and viscosity was confirmed.