Dairy Systems - Practical Food Rheology - page 150

Storage modulus (G ), loss modulus (G ) and phase angle (

Fig. 7.5 ) over changing

frequencies for process cheeses at 4 days of age (from Brown, 2002, to Brown et al.,
2003).

δ

texture can be explained by using small strain rheology and correlat-
ing the rheological properties to microstructure. As previously stated,
the limit of LVE region must be determined before any measurement.
Typical viscoelastic characterisation of cheese is shown in Fig. 7.5. The
magnitude of G was higher for all samples than the magnitude of G ,
and G increased with increasing frequency. These trends are gener-
ally observed with weak gels (Kavanagh and Ross-Murphy, 1998) and
cheeses (Nolan et al ., 1989; Ma et al ., 1996; Tunick, 2000). At very low
frequencies (0.001 Hz), is relatively high, indicating the dominant ef-

fect of the viscous component; the cheeses behave more fluid-like when
deformed at slower speeds. When the frequency is increased from 0.01
to 1.0 Hz,

δ

levels, showing that the speed has less of an influence on
the relative effects of the viscoelastic properties. At very high frequen-
cies,

δ

is low, showing the dominant effect of the elastic component; the
cheeses behave more 'solid-like' at such higher speeds (Brown, 2002).
The most important factor affecting rheological and physical prop-
erties of cheese during ripening is proteolysis, which contributes to the
final texture of cheese. Decreasing G during ripening has been observed
in mozzarella (Tunick et al ., 1993a, 1993b). The casein matrix becomes
softer and less elastic due to the breakdown of α S1 casein, which pro-
vides the major contribution to the structure of caseins in curd. Similarly,
Subramanian and Gunasekaran (1997) found that the strain limit of the
LVE region of mozzarella cheese decreased with age and increasing
temperature and hypothesised that this was due to proteolysis and ther-
mal softening over time. Change in G and loss tangent during ripening
has been reported for cheddar cheese (Lucey et al ., 2003; Lucey et al .,
2005). G values determined at 40 and 80 ◦ C decreased during ripening
especially during the first 60 days. At low temperature (5-35 ◦ C), there
was no significant difference in loss tangent among cheddar cheeses.
Loss tangent increased during ripening when measured at 40-60 ◦ C.

δ