3.2. DSC method
The DSC method can be used to obtain the freezing point, heat
of fusion (DH) and apparent specific heat. Fig. 3 shows a typical
endothermic curve of the tilapia fish burger illustrating the peak
and onset points. The onset of melting was considered as the freezing
point (Bai et al., 2001). Tf and DH of tilapia fish burger was
(2.8 ± 0.4) C and (136.4 ± 16.6) J/g, respectively. Tf was not
significantly different from the Tf (2.7 ± 0.1 C) obtained by the
cooling curve method using household freezer. This result
validated that both methods can be used to determine freezing
points of high moisture foods, such as fish burger.
Apparent specific heat (Cpapp) between temperature range 20
to 0 C, where phase change happened, increased rapidly from 0 to
30 J/g C. Matuda et al. (2011) found that Cpapp of bread dough
increased sharply from 2 to 15 J/g C between the temperature
range from 20 to 0 C.
Chen and Pan (1995) found similar values for the Tf of tilapia
(Oreochromis sp.) meat with 80.3% moisture using the two methods,
ranging from 1.03 C (DSC method) to 0.86 C (cooling
curve). To the extent of our knowledge, no previous studies
determined the Tf of fish burger made from tilapia meat. It is
known that Tf varies greatly for different seafoods and fish species,
as reported by Rahman and Driscoll (1994). The authors found Tf
values ranging from 0.5 C to 2.07 C for invertebrate seafoods
using the cooling curve methods. Shrimp with 75.7% moisture
had Tf of 2.07 C, which was similar to the value found in this
study for fish burger with 72% moisture. Freezing point for
haddock with 80.3% moisture varied from 1.0 C (Murakami
and Okos, 1989) to 2.94 C (Charm and Moody, 1966).