Chemistry Reference
In-Depth Information
Change in formulation also affects viscoelastic characterisation of
cheese. Reducing the amount of fat in cheese has been known to cause
an increase in elastic component (
G
) of cheese. Low fat mozzarella
cheese has a higher
G
,
G
,and
*
compared to full-fat cheese at the
same age (Tunick
et al
., 1993a). Hennelly
et al
. (2006) investigated the
effect of inulin (fat substitute) on rheological properties of imitation
cheese. At 22
◦
C, there was no significant difference between
G
and
G
of cheeses containing different amounts of inulin. However, when
cheeses without inulin were heated from 22 to 90
◦
C,
G
decreased and
tan
η
increased with heating temperature, indicating the weakening of
the protein-protein interaction within the casein network. For imitation
cheeses with high inulin concentration (
δ
>
13.1% w/w),
G
started to
55
◦
Candtan
>
δ
increase at
values gradually increased with increasing
temperature to about 55
◦
C and then decreased at higher temperature,
reflecting a strengthening of the cheese matrix at these temperatures.
Small amplitude test can be used to study the effect of cheese process-
ing parameters. Homogenising milk or processing at higher temperature
causes an increase in
G
of mozzarella cheese (Tunick
et al
., 1993a). The
effect of pH on rheological properties and the microstructure of process
cheese was investigated by Marchesseau
et al
. (1997). The dependence
of firmness on pH was shown by a decrease in
G
as pH increased from
5.7 to 6.7 and when pH decreased from 5.7 to 5.2. In agreement with
the rheological results, the microstructure of process cheese at pH 5.2
(lowest
G
) had a highly distorted structure that included large spher-
ical particles. As pH was increased to 5.7, the cheese microstructure
consisted of more homogeneous and dense network with a clear sepa-
ration between fat globules and the protein network. At pH 6.7, small
condensed aggregates were formed and appeared to disrupt the protein
matrix. A very logical application of small strain oscillatory tests is the
characterisation of melting properties. Mounsey and O'Riordan (1999)
studied the melting properties of imitation cheeses by comparing tan
δ
of different cheeses as a function of temperature. When temperature
was increased from 22 to 90
◦
C, the tan
δ
values for the cheese with
0-9% pregelatinised maize starch increased, indicating that the elastic
component decreased to a greater extent than the viscous component.
The observed maximum tan
values decreased with increasing starch
content, reflecting the tendency of starch to hinder meltability. Imitation
cheeses containing starch maintained their elastic properties on heating
to a higher degree than control samples. A high correlation was found
between maximum tan
δ
values and meltability determined by an em-
pirical melt test. Another investigation (Ustunol
et al
., 1994) suggested
that complex modulus (
G
*
) could be a useful predictor of meltability
of full-fat and reduced-fat cheddar cheeses as measured by the Arnott
test.
δ
