The freezing time and freezing rate measured during sample
trial are presented in Table 2. Freezing times and freezing rates
for both temperature ranges (0 to 5 C and 0 to 18 C) measured
were significantly different. The freezing time measured between 0
and 5 C represents the zone where most ice crystals form (Chen
and Pan, 1997) or the critical zone (Fellows and Freezing, 2000). As
reported by Fellows and Freezing (2000), the time a food stays at
the critical zone determines the number and the size of ice crystals.
Consequently, the process can be classified as a slow and fast
freezing. Chen and Pan (1997) found that higher freezing rates
maintained better the integrity of tilapia muscle. Another important
quality factor is the weight loss during freezing. Weight losses
occur due to sublimation of the surface ice, which can affect the
product appearance, texture and flavor (Campañone et al., 2001).
According to Johnston et al. (1994), the weight loss ranges from
0.5% to 1% for fish frozen by forced-air and plate freezing.