KEY TAKEAWAYS
- Freezing beef rib primals at -20 °C or -80 °C provided little to no differences in terms of color, tenderness, or oxidative status.
- Thawing is an important factor to consider, as fast thawing decreases water loss, potentially resulting in beef with superior juiciness and yield.
- Multiple freezing/thawing cycles progressively decrease the overall quality of the beef and should be avoided if possible.
BACKGROUND
Fresh meat is crucial in providing essential nutrients and ensuring food security for consumers. However, guaranteeing meat's safety and quality during transportation and storage presents inherent challenges and necessitates the use of preservation techniques. Freezing is a commonly employed preservation method in the meat industry to prevent spoilage and deterioration. Despite being arguably the best form of storage for fresh meat, improper freezing conditions can negatively impact many of the quality characteristics it intends to preserve, such as color, texture, and juiciness. Therefore, these products may fail to meet consumer expectations, ultimately leading to economic losses.
During the freezing process of beef, water begins forming ice crystals of various sizes and shapes. In general, a slow freezing rate promotes the formation of large ice crystals, leading to significant structural damage to the meat upon thawing. While this may improve product tenderness, the damage to cellular structures and membranes impairs beef’s ability to retain water, thereby negatively impacting yield, color and juiciness. Conversely, a fast freezing rate typically involves the formation of smaller ice crystals, and subsequently the meat is less likely to sustain mechanical damage and quality loss after thawing. When evaluating the overall effect freezing storage has on fresh meat, it is crucial to consider the impact of the thawing rate. The rate at which frozen meat thaws significantly determines its quality, though this relationship is not well characterized. In general, if the rate of thawing exceeds the rate of water reabsorption by the dehydrated fibers, then more water will be exuded from the meat
The objective of this study was to assess the physiochemical and ultrastructural changes occurring in whole beef ribs in response to different freezing/thawing treatments.
Methodology
Forty USDA Choice rib primals of similar weight (6.53 ± 0.07 kg) were purchased from a local USDA-inspected beef processing plant 48 h postmortem. Primals randomly divided into five experimental groups (8 ribs per group). The first group served as a control (no freezing), while the second group was frozen in an ultralow temperature freezer at −80 °C (fast freezing), stored in the same freezer for 12 weeks, and thawed at 4 °C for 48 h (slow thawing). The third group was frozen in a −20 °C freezer (slow freezing), stored in the same freezer for 12 weeks, and thawed at 4 °C for 48 h. The fourth and fifth groups were frozen and stored the same manner as groups 2 and 3, respectively, but thawed in a water bath (12 ± 1 °C) for 12 h (fast thawing). Following freezing and thawing treatments ribs were fabricated into steaks. Steaks were grouped based on their location: four cranial, five medial, and four caudal.
Generally, the first freezing/thawing cycle increased tenderness, a*, b*, and drip loss compared to the control (P < 0.05), with notable degradation observed in ultrastructural micrographs. However, the fast freezing/fast thawing and slow freezing/fast thawing treatments reduced drip loss compared to the fast freezing/slow thawing and slow freezing/slow thawing (P < 0.05). The second freezing/thawing cycle further influenced meat quality, decreasing a* and b*, increasing tenderness and TBARS, and accentuating ultrastructural deterioration (P < 0.05). Variations were detected among sampling locations for most of the tested quality parameters, particularly after freezing/thawing cycle 1. The pH of the three sampling locations did not differ within each of the five treatments. After the first freezing cycle, drip loss was greater for steaks in the slow freezing/fast thawing treatment than those in the control (no freezing) and fast freezing/fast thawing treatments (P ≤ 0.04). Nevertheless, a* values of each sampling location in the fast freezing/fast thawing, fast freezing/slow thawing, slow freezing/fast thawing, and slow freezing/slow thawing treatments of freezing/thawing cycle 1 were greater than those of freezing/thawing cycle 2 (P ≤ 0.001). Steaks in the fast freezing/slow thawing, slow freezing/fast thawing, and slow freezing/slow thawing treatments of freezing/thawing cycle 2 had lower b* values when compared to their freezing/thawing cycle 1 counterparts (P ≤ 0.002). In contrast, a* and b* values generally showed greater values in the four freezing/thawing treatments compared to the control of cycle 1, but lower than the control after cycle 2.
The slow freezing/fast thawing and slow freezing/slow thawing treatments of freezing cycle 2 possessed lower WBSF values than their freezing/thawing cycle 1 counterparts (P ≤ 0.02). All freezing/thawing treatments improved beef tenderness in the current study compared to the control treatment. When comparing the two cycles, TBARS of all sampling locations within the fast freezing/fast thawing, slow freezing/fast thawing, and slow freezing/slow thawing treatment groups were greater in cycle 2 (P ≤ 0.02). TBARS values for slow freezing/fast thawing were not different between the two cycles. No differences in TBARS were observed between the five treatments after freezing/thawing cycle 1, but the fast freezing/fast thawing, fast freezing/slow thawing, slow freezing/fast thawing, and slow freezing/slow thawing treatment groups had generally greater TBARS after cycle 2 than the control.
Implications
Freezing and thawing practices can be conducted while maintaining product quality. Overall, no major differences in meat quality were detected between samples frozen at −20 °C and those frozen at −80 °C. However, we recommend employing rapid thawing methods, as they appear to mitigate the loss of product quality. Product that is subjected to progressive freezing and thawing cycles is at a greater risk for declines in product quality.