Kinetic Modeling of Myofibrillar Degradation, Shear Force, and Microbial Growth During Beef Accelerated Aging by the Freeze/Thaw Process

Aging has been the main industrial practice for improving beef palatability, but it requires up to 21 days of cooler storage to reach the desired tenderness. As an alternative to accelerate the aging process, both the prior freezing/thawing process and the storage at high temperatures have been suggested. This study aimed to develop kinetic models to evaluate the effects of freezing/thawing process and different aging temperatures (1, 7, 14 and 20 °C) on vacuum-packed Nellore beef steaks. Changes on fragmentation index (FI), shear force (SF), cooking loss (CL) and total bacteria count (TBC) of raw beef during aging followed a first-order kinetic model. The reaction rate constant (k) increases with increasing aging temperature, and the activation energy (Ea) was lower in frozen/thawed samples than nonfrozen ones for FI (13 vs 24 kJ/mol) and SF (25 vs 47 kJ/mol). The increase in aging temperature had a lower effect on the FI and SF of frozen/thawed samples than on the nonfrozen ones. Frozen/thawed samples required a shorter aging time than nonfrozen samples to reach the same SF. CL was affected only by aging temperature. The specific growth rate (µ) of TBC increases with increasing aging temperature, but the Ea (51 kJ/mol) was not affected by the freezing/thawing process. The developed kinetic models provide a deeper understanding of the mechanism of the quality changes of frozen/thawed beef during aging and suggest that the increased tenderization in the frozen/thawed samples is primarily due to cellular damage rather than the increase in proteolysis rate.