Deep chill (DC) is a system that allows boxed beef subprimals to hover immediately above their respective freezing point (> -3.05°C) to maintain their "fresh" status while slows down the growth rate of spoilage microflora, improve tenderness and therefore palatability. The DC program has grown as many large retail chains and restaurant establishments have increasingly utilized it. The DC program enables buyers to have a product held for weeks or even months (≤ 90 days), then delivered to them equivalent to a fresh product in terms of moisture, tenderness, and color stability. As the DC program continues to grow, research is needed to refine the process and develop a user guide for processing bone-in and boneless beef products following DC storage. The objectives of this study were to determine the impact of 60, 75, and 90 days of DC storage on (i) tenderness and consistency of consumer sensory ratings of beef cuts, (ii) retail shelf-life capability (microbial and visual lean color), (iii) subprimal yields, and (iv) the "ceiling" in terms of storage time.
Paired (10 pairs each) USDA Top Choice beef inside rounds (IR), export ribs (RE), and boneless strip loins (SL) were collected from 10 carcasses and subjected to 60, 75, or 90 days of DC (-3°C). After each DC storage time, the percentage of purge loss was measured, and samples were fabricated into steaks and placed into a retail display case (3°C) for 7 d. All steaks were evaluated for instrumental (lightness L*, redness a*, and yellowness b*) and visual (lean color, discoloration, fat color, overall appearance, and fat and bone color when applicable) color daily during retail display. Additionally, on days 0, 2, 4, and 7 of retail display, steaks were analyzed for aerobic microbial populations (APC), lactic acid bacteria (LAB) counts, and Pseudomonas spp. counts. Warner-Bratzler shear force (WBSF), cooking loss, and consumer sensory analyses were conducted on steaks from all DC storage times, and on samples subjected to 21 d of wet-aging at 3°C (i.e., control; no DC storage). A split-plot design was used to evaluate (i) the effects of DC storage time and days in retail display on color (instrumental and visual), and (ii) the effects of DC storage time on purge loss, cooking loss, WBSF, and sensory evaluation. For microbial analysis, the experiment was designed as a 4 (DC storage times) × 4 (sampling times) factorial for each cut (IR, RE, and SL) and bacterial count type (APC, LAB, and Pseudomonas spp.).
The purge percentage tended to increased gradually with DC storage time, regardless of the cut, but only IR had a significant increase. In general, L*, a*, b* initial color values (day-0) of IR, RE, and SL increased with storage time and decreased during retail display. Trained color panelists did not find differences in lean color, discoloration percentage, and overall appearance of samples under the different DC storages, regardless of the cut evaluated. For microbial analysis results, overall, regardless of DC storage time, APC, LAB counts, and Pseudomonas spp. counts of IR and SL steaks remained below 7 log CFU/cm2 up to day 4 of retail display. However, on day-4, APC of RE steaks from DC75, and DC90 reached 7 log CFU/cm2, as well as LAB counts recovered from RE samples from DC90. These results could suggest a microbial storage shelf-life of 90 d and following retail display of three to four days, regardless of the cut, when beef is held in DC. No apparent effects on cooking loss were observed irrespective of cut and DC storage. In addition, WBSF values decreased over storage time, and perceived tenderness by consumers increased without an adverse effect on juiciness, flavor, and overall liking.
The data from this study may be useful for the meat industry when considering extending the storage time for supply stabilization or extended shipment for export markets of beef products under low controlled temperatures.