Loin steaks from 78 carcasses of A, B, C and E maturities were categorized into three tenderness groups on the hasis of sensory tenderness scores and Warner-Bratzler (W-B) shear force values. Myofibril fragmentation index (MFI), sarcomere length, total and soluble collagen, moisture, fat and pH values were determined for these steaks. Carcass characteristics were also measured. The physical, chemical and sensory values were statistically analyzed to determine the relationship of these values, especially the relationship and the importance of myofibril fragmentation to tenderness of loin steaks. Results of this study showed that myofibril fragmentation index (MFI) accounted for more than 50% of the variation in loin steak tenderness and that myofibril fragmentation was a more important effector of tenderness in loin steaks than collagen solubility or sarcomere length. The steaks used in this study varied widely in marbling degree and maturity; therefore, MFI should be an excellent predictor of broiled loin steak tenderness. Although a number of significant correlations were observed between MFI and carcass characteristics, none of these was of practical importance because they accounted for little of the variation in tenderness.

A study was conducted to determine consumer perceptions of beef top loin steaks of known shear force and to evaluate how buying trends were modified by the tenderness and price variations of these steaks. Strip loins were cut into a 2.54-cm-thick steaks, and the center steak from each strip loin was used to determine Warner-Bratzler shear force. The remaining steaks were placed into one of the following shear force categories based on that shear force and color-coded accordingly: 1) 2.27 to 3.58 kg (Red); 2) 4.08 to 5.40 kg (White); and 3) 5.90 to 7.21 kg (Blue). Randomly recruited consumers were allowed to evaluate steaks and then purchase steaks based on their findings. A $1.10/kg price difference was placed between each category. Results of the analysis indicated that consumers were able to differentiate between the three categories of tenderness (P < .05). In addition, consumers gave higher (P < .05) juiciness and flavor ratings to Red steaks than to Blue steaks. Overall satisfaction was higher (P < .05) for Red steaks than for the other two categories of steaks. The following percentages of steaks were purchased: 1) Red, 94.6%; 2) White, 3.6%; and 3) Blue, 1.8%. These results suggest that consumers could discern between categories of tenderness and were willing to pay a premium for improved tenderness.

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To determine the average tenderness and sensory ratings of beef subprimal cuts sold in retail cases across the United States, retail cuts were purchased through typical retail outlets in 14 metropolitan cities and transported to Texas A&M University for sensory and Warner-Bratzler shear analysis. The overall mean shear force for all cuts was 3.65 kg, and the mean shear force values for chuck, rib, loin, and round cuts were 3.72, 3.36, 3.17, and 4.31 kg, respectively. No difference (P greater than .05) in tenderness was detected among the cuts from the rib. Mean palatability ratings and shear force values of top loin steaks were similar to those of rib cuts. Top sirloin steaks were tougher (P less than .05) and received the lowest sensory ratings compared with other loin cuts. Approximately two to three times as many round and chuck steaks had shear force values in excess of 4.6 kg compared with their roast counterparts. In all cases, roasts tended to be more tender than steaks from the same subprimal source. USDA Choice chuck retail cuts, compared to Select and No-roll chuck cuts, had approximately 10% fewer cuts with shear force values in excess of 4.0 kg. More work is needed to improve meat tenderness, primarily for retail cuts from the round and chuck primals. Future research must investigate the interaction of antemortem and postmortem factors associated with variation in beef tenderness.

A high glycogen level may be beneficial to the ischemic heart by providing glycolytic ATP or detrimental by increasing intracellular lactate and protons. To determine the effect of high glycogen on the ischemic myocardium, the glycogen content of Langendorff-perfused rat hearts was either depleted or elevated before 32 minutes of low-flow (0.5 mL/min) ischemia with Krebs-Henseleit buffer with or without 11 mmol/L glucose, followed by 32 minutes of reperfusion with buffer containing 11 mmol/L glucose. 31P nuclear magnetic resonance spectra were acquired sequentially throughout. Further experiments involved early reperfusion or the addition of HOE 694, a Na+-H+ exchange inhibitor, during reperfusion. When glucose was supplied throughout ischemia, no ischemic contracture occurred, and postischemic recovery of contractile function was highest, at 88% of preischemic function. In the absence of glucose, normal-glycogen hearts underwent ischemic contracture at 5 minutes, had an end-ischemic pH of 6.87, and recovered to 54%, whereas in high-glycogen hearts, contracture was delayed to 13 minutes, the end-ischemic pH was 6.61, and functional recovery decreased to 13%. Contracture onset coincided with the decrease in glycolysis, which occurred as glycogen became fully depleted. Functional recovery in the high-glycogen hearts increased to 89% when reperfused before contracture and to 56% when reperfused in the presence of HOE 694. Thus, during brief ischemia in the high-glycogen hearts, ischemic glycogen depletion and contracture were avoided, and the hearts were protected from injury. In contrast, during prolonged ischemia in the high-glycogen hearts, glycogen became fully depleted, and myocardial injury occurred; the injury was exacerbated by the lower ischemia pH in these hearts, leading to increased Na+-H+ exchange during reperfusion. The contradictory findings of past studies concerning the effect of high glycogen on the ischemic myocardium may thus be due to differences in the extent of glycogen depletion during ischemia.

Threshold Warner-Bratzler shear (w;sS) values were determined by regression analysis of WBS force values and trained sensory panel overall tenderness ratings of beef top loin steaksfrom A-and B-maturity carcasses (n = 678).Guidelines for retail and foodservice beef were based on 50 and 68% confidence levels, respectively, for overall tenderness ratings of "slightly tender. '' Due to the extreme variation in tenderness that exists in the current U.S. beef population, more stringent confidence levels were not practical. Threshold WBS values f o r retail and foodservice beef were 4.6 and 3.9 kg, respectively. When these values were tested against the population of beef in the National Consumer Retail Beef Study, the 4.6 kg value was 88.6% accurate at determining whether or not a steak would be rated less than "slightly tender '' by consumers.