Key Findings

• Aging prior to freezing significantly enhances meat quality attributes by reducing freeze/thaw loss and drip loss.
• The results of the present study suggest that developing an optimal aging/freezing strategy has the potential to improve meat quality attributes of frozen/thawed beef while consistently offering the preservation benefits of freezing.
• These findings offer practical insights for the meat industry, promoting cost-effective strategies to elevate meat quality, reduce waste, and enhance overall sustainability. 

background

Freezing is a widely adopted method to extend the shelf-life of meat products, ensuring convenience in transportation, storage, and retail. However, freezing is known to adversely affect meat quality, especially increased purge and thaw loss, reduced water-holding capacity (WHC), texture degradation, and color instability. Furthermore, repeated freezing and thawing cycles exacerbate these negative effects, causing additional structural and quality deterioration. Thus, there exists a critical need for developing novel freezing practices that produce frozen/thawed beef products with improved quality attributes. Postmortem aging is a standard practice aimed at enhancing meat quality. During aging, endogenous proteolytic enzymes such as calpains and cathepsins degrade myofibrillar proteins, weakening the muscle fiber structure and improving tenderness and WHC. The beneficial impacts of aging before freezing on minimizing quality defects associated with frozen/thawed meat have been reported. Despite extensive research on the effects of aging, freezing, and thawing on meat quality individually, there is a still knowledge gap in understanding the combined impact of aging and repeated freezing/thawing on meat quality attributes. This study aims to elucidate the effects of different aging durations before freezing on quality attributes, physicochemical and biochemical properties, and sensory attributes of beef loins and sirloins, particularly under repeated freeze/thaw conditions. The hypothesis of this project is that aging meat before freezing will enhance the overall quality of frozen/thawed meat, even when it undergoes multiple freeze/thaw cycles.

methodology

Two separate experiments were conducted to achieve the research objectives.   

Experiment 1 (Loin):

At 2-day postmortem, 60 strip loins (m. longissimus lumborum) were collected from 30 beef carcasses (USDA Top Choice) and divided into four groups of different aging times (0, 2, 3, and 4 weeks) at 2^oC and then frozen for 5, 3, 2, and 1 week, respectively. Prior to freezing, subsections were collected from loins at each assigned aging time serving as never-frozen samples. Also, additional sections from the loins assigned 4 weeks of aging were collected and aged for one additional week serving as 5 weeks of never frozen control. After completion of the first freezing, the loins were thawed for 2 days in a cooler and a portion of samples was collected for freeze-thaw loss, display weight loss, Warner-Bratzler shear force (WBSF), and display meat color measurements. The remaining sections were repeatedly frozen for an additional 5 weeks, thawed, and analyzed for the above-mentioned meat quality analyses. Consumer sensory evaluation (n = 90) was conducted for eating quality attributes.   

Experiment 2 (Sirloin):          

At 5 days postmortem, pairs of 40 sirloins (gluteus medius) were collected from 20 beef carcasses (USDA Choice). Each sirloin was randomly assigned to no further aging (A0) or 4 weeks of aging (A4). Subsections were taken for initial samples, then subjected to either single freezing-thawing (A0FT and A4FT) or repeated freezing-thawing (A0FT×2 and A4FT×2) conditions for three weeks. Following aging (2°C), freezing (-20°C), and thawing (2°C), the samples were evaluated for color, Warner-Bratzler shear force (WBSF), water-holding capacity (WHC), myofibrillar fragmentation index (MFI), lipid oxidation (TBARS) and consumer panel sensory evaluation (n = 120).

results and discussion

The results from both loin and sirloin studies conclusively show that aging prior to freezing significantly enhances meat quality attributes by reducing freeze/thaw loss and drip loss. This improvement in water-holding capacity is consistent across both types of meat. Both studies demonstrated the effect of aging on improving water-holding capacity which could alleviate the deteriorative effect of freezing and repeated freeze-thawing, as evidenced by reduced freeze-thaw losses and display losses. Aging would provide protective effects against water loss during freezing and thawing processes by creating a more permeable matrix with enhanced enzymatic activity. Tenderness exhibited significant improvements with aging. Meanwhile, the repeatedly frozen sample was comparable to that of five-week-aged never-frozen control, suggesting a potential avenue for enhancing tenderness through strategic freezing. In non-aged meat, freezing alone increases tenderness. The sirloin study suggested that aged and double-frozen meat was more tender compared to other treatments. The consumer sensory panels in both studies did not report any negative impact of repeated freeze/thaw cycles on meat quality. Moreover, the panelists in the sirloin study reported improved tenderness and rated aged, double-frozen meat as premium quality meat compared to other treatments. The results of the present study suggest that developing an optimal aging/freezing strategy has the potential to improve the meat quality attributes of frozen/thawed beef while consistently offering the preservation benefits of freezing.

industry Implications

The study outcomes underscore the effectiveness of aging before freezing and repeated freezing in ameliorating water loss, improving tenderness, and ensuring consumer satisfaction. The stepwise aged/frozen process, characterized by superior tenderness and improved water-holding capacity, will positively influence consumer perception and satisfaction as well as market acceptance. These findings offer practical insights for the meat industry, promoting cost-effective strategies to elevate meat quality, reduce waste, and enhance overall sustainability. Furthermore, the results of the current study determined that cryo-damage-induced meat tenderization by freezing coupled with aging deserves further investigation at the molecular level to elucidate the underlying mechanism and to develop a practical post-harvest processing strategy.