Dynamic oscillation tests were conducted to determine the flow
behavior and characterize the viscoelastic properties of yogurt, using a
rheometer fitted with a 40-mmdiameter
cone and 2° cone angle and plate geometry with a 4 mmgap.
To ascertain the applicable stress and frequency in which storage
modulus (G′) and loss modulus (G″) parameters of yogurt would
demonstrate a linear constant rate, dynamic frequency ramp tests and
dynamic stress ramp tests were conducted at 25 °C (range of
frequency from 1 to 10 Hz and stress set as 3 Pa and range of stress
from 1 to 10 Pa and frequency set as 2.5 Hz, respectively). Dynamic
temperature ramp tests were done at stress and frequency of 1.0 Pa
and 2.0 Hz, respectively, in a temperature range of 4 to 50 °C (heating)
and 50 to 4 °C (cooling), at a rate of 7 °C/min. Aliquots of the samples
were carefully removed from the undisturbed yogurt cup and placed
on the center of the rheometer plate; the top plate was slowly
lowered on the top of the sample prior to analysis.