The Effect of Aging/Freezing Sequence and Freezing Rate on Quality Attributes of Beef Loins (M. longissimus lumborum)

The objective of this study was to determine the effect of different aging/freezing sequences combined with different freezing rates on quality attributes of beef loins (M. longissimus lumborum). Loins from 1 side of 8 beef carcasses (USDA Low Choice grade) were obtained at 2 d postmortem, cut into 10 steaks (2.54 cm), and randomly assigned into 5 treatments, where factorial combinations of 2 aging/freezing sequences (aging first then freezing/thawing [AFT] and freezing first then thawing/aging [FTA]) and 2 freezing rates (fast freezing [FF] and slow freezing [SF]) were used and compared to an aged only (AO) treatment as a control. Samples frozen using the FF condition were found to have a critical freezing time (Tc) of 21.5 min while the SF counterpart had a Tc of 175 min. Histological observation showed more visually enlarged gaps between muscle fibers in the SF samples, regardless of aging/freezing sequence. The SF-FTA samples had a significantly higher purge/ thaw loss followed by FF-FTA, while the loss from FF-AFT, SF-AFT, and AO were not different from each other (P > 0.05), suggesting that freezing rate effect might be more profound when applied in FTA. Cook loss was higher in AO compared to both FTA treatments (P < 0.05); however, it was not different when compared to AFT (P > 0.05). A lower shear force value and higher troponin-T protein degradation were found in both AFT and FTA compared to AO (P < 0.05), which would be attributed to the ice-crystal damage due to freezing. These results suggest that aging/freezing sequence could be an overriding factor in determining major meat quality attributes of frozen/thawed meat over freezing rate. However, fast freezing could negate some quality defects associated with the FTA process.