Dynamic rheology
Fig. 5 shows the value of loss tangent vs. time for control
and calcium fortified fruit yogurt. Phase angle (tan d) is
associated with degree of viscoelasticity of sample. A low
value of tan d indicates that the gel has more elastic
character (more solid like) (Lucey, 2002). There was
no significant (P40.05) difference in the loss tangent
of control and calcium fortified fruit yogurt at all
(1st, 7th, and 14th) days of storage. This indicates that
the control and calcium fortified fruit yogurt have similar
viscoelastic characteristics and there is no significant
change in the bonding involved in the formation of
gel structure. WHC, apparent viscosity analysis, and
flow behavior results showed greater gel strength of
calcium fortified fruit yogurt when compared to control
fruit yogurt which could be attributed to function of
calcium as a cross-link between protein molecules. Therefore,
in calcium fortified fruit yogurt, the nature of bonding
did not change but the extent of cross-linking increased
due to presence of dissolved calcium. Storage of samples
for 1 week did not cause any significant change in the
viscoelastic properties of samples from that on 1st day.