Physico-chemical and processing quality of porcine M. longissimus dorsi frozen at different temperatures

Longissimus dorsi muscle from six pigs (24 h post-mortem) was cut into portions of similar size and shape (c. 700 g) and vacuum-packed in polyfilm. The muscle specimens were divided into three samples, one frozen at -20°C, another at -80°C and the third served as the control (not frozen). The meat sample frozen at -80°C was transferred to the -20°C freezer. After one month, both frozen pork samples were thawed at -2°C and drip loss (%) was measured. Hunter colour, metmyoglobin (MetMb) formation (%), water-holding capacity (WHC), TBA value, transmission value (TM) and myofibril fragmentation were also determined. There was no significant difference in drip loss for the two frozen samples. No MetMb formation could be detected and Hunter values were basically the same for all three samples. WHC, TBA value and TM were essentially the same for all three samples. TBA value was quite low for each frozen sample, indicating that lipid oxidation did not occur during freezing. Histological examination of both frozen samples indicated inter- and intracellular ice crystal formation at -20°C, and intracellular ice at -80°C, the extent being less than at -20°C. At -20°C, ice crystals were larger and muscle fibre diameter smaller than for the control or -80°C sample. Myofibril fragmentation in both frozen samples was significantly higher than in the control. Pork sausage was prepared from all three samples by adding 2% NaCl and 100 ppm NaNO₂. Cooking loss and colour forming ratios were essentially the same. The sausage sample made from the -20°C frozen meat was harder than that of the other two samples according to rheological measurement.