Postmortem (PM) and mu-calpain-induced degradation of specific skeletal muscle proteins was monitored by SDS-PAGE and Western blotting. Samples were removed from bovine longissimus thoracis (LT) at approximately 45 min PM for the preparation of at-death (0-d) myofibrils (MF). The LT was excised at 1 d PM, vacuum-packaged, and stored at 2 degrees C. Samples were removed for Warner-Bratzler shear force analysis and biochemical analysis at 1, 3, 7, 14, 28, and 56 d PM. The protease mu-calpain was purified from bovine skeletal muscle and used to digest at-death MF at pH 5.6, 4 degrees C, 100 microM CaCl2. Degradation of the proteins titin, nebulin, filamin, desmin, and troponin-T was monitored in the PM and mucalpain-digested samples by using SDS-PAGE and Western blotting. The PM samples that had significantly lower shear force (LSF) values (P < .05) at 1 d PM exhibited faster degradation of these five proteins than the higher shear force (HSF) samples. In LSF samples, the intact titin band (T1) was absent by 7 d PM and nebulin was absent by 3 d PM. In LSF samples, some filamin was degraded by 3 d PM, but in HSF samples degradation was not apparent until 14 d PM. In LSF samples, desmin was degraded more rapidly PM than in HSF samples. Troponin-T was broken down PM to yield two major polypeptides of approximately 28 and 30 kDa; these polypeptides appeared earlier PM in LSF samples. Degradation products, similar to those observed PM, for all five proteins also were detected in Western blots of mu-calpain-digested MF, suggesting the calpain system plays a key role in PM protein degradation. ABSTRACT:Postmortem (PM) and m-calpaininduced degradation of specific skeletal muscle proteins was monitored by SDS-PAGE and Western blotting. Samples were removed from bovine longissimus thoracis ( L T ) at approximately 45 min PM for the preparation of at-death (0-d) myofibrils (MF). The LT was excised at 1 d PM, vacuum-packaged, and stored at 2°C. Samples were removed for WarnerBratzler shear force analysis and biochemical analysis at 1, 3, 7, 14, 28, and 56 d PM. The protease m-calpain was purified from bovine skeletal muscle and used to digest at-death MF at pH 5.6, 4°C, 100 mM CaCl 2 . Degradation of the proteins titin, nebulin, filamin, desmin, and troponin-T was monitored in the PM and m-calpain-digested samples by using SDS-PAGE and Western blotting. The PM samples that had significantly lower shear force (LSF) values ( P < .05) at 1 d PM exhibited faster degradation of these five proteins than the higher shear force (HSF) samples. In LSF samples, the intact titin band ( T 1 ) was absent by 7 d PM and nebulin was absent by 3 d PM. In LSF samples, some filamin was degraded by 3 d PM, but in HSF samples degradation was not apparent until 14 d PM. In LSF samples, desmin was degraded more rapidly PM than in HSF samples. Troponin-T was broken down PM to yield two major polypeptides of approximately 28 and 30 kDa; these polypeptides appeared earlier PM in LSF samples. Degradation products, similar to those observed PM, ...

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.

Samples were removed from bovine longissimus (L), semitendinosus (ST) and psoas major (PM) muscles at 1, 2, 3, 6, 7, 10 or 13 days postmortem stored at 2°C or 25°C. Myofibril fragmentation index (MFI) and Warner-Bratzler (W-B) shear-force values were determined on steaks from each muscle. Myofibril fragmentation index (MFI) was determined quantitatively by measuring the absorbance of a myofibril suspension. It was observed that MFI increased during postmortem storage for L and ST, but increased only slightly for PM. These results paralleled those changes in myofibrils observed with phase and polarized light microscopy. Both MFI and W-B shear-force values changed greatly from 1 to 3 days postmortem with a lesser change occurring after 3 days in L and ST muscles. In PM muscle, however, only a slight change in MFI and W-B shear-force occurred during postmortem storage. Elevated storage temperature (25°C) caused an accelerated change in both MFI and W-B shear-force in L and ST muscles; however, storage temperature had little effect on PM muscle. L and ST muscles responded similarly to postmortem storage, but PM muscle was characteristically different from the L and ST muscles. These findings demonstrate the differences and similarities of muscles to postmortem storage and further elucidate the role of myofibrillar proteins in meat tenderness.

Conjugated linoleic acid (CLA) is a collective term for positional and geometric isomers of linoleic acid. Dietary CLA has been shown to improve feed efficiency, decrease body fat, and increase lean tissue in laboratory animals. We hypothesized that CLA would improve performance and carcass composition and would be deposited in pork tissues. Diets of 40 crossbred pigs were supplemented with CLA to determine its effects on performance and carcass composition. Eight replications of five littermate barrows with an initial average weight of 26.3 kg were allotted at random to individual pens. Within replication dietary treatments containing 0, 0.12, 0.25, 0.5, or 1.0% CLA were assigned at random. Pigs were weighed and feed disappearance was determined at 14-d intervals. Average daily gain increased linearly as the level of CLA increased in the diet (P < 0.05). Average daily feed intake was not affected by the concentration of CLA in the diet. Therefore, a linear increase in gain:feed ratio (P < 0.05) was observed. Carcasses from animals fed control diets had greater 10th rib backfat than carcasses from animals fed CLA (P < 0.05). Ultrasound measurement and carcass measurements showed less fat depth over the loin eye at the 10th rib of pigs fed doses of CLA (P < 0.05) than that observed for control pigs. Belly hardness (firmness) increased linearly as the concentration of CLA in the diet increased when bellies were measured for firmness either lean side up (P < 0.001) or lean side down (P < 0.05). Loin dissection data demonstrated that CLA produced a quadratic treatment effect both for less intermuscular fat (P < 0.001) and less subcutaneous fat (P < 0.05) and a linear increase for bone (P < 0.05), although finished loin weight only tended to increase (P = 0.08). The CLA concentration increased in a linear relationship in both subcutaneous fat (P < 0.001) and lean tissue (P < 0.001). Dietary CLA was incorporated into pig tissues and had positive effects on performance and body composition.

This study was conducted to determine degradation of the giant myofibrillar proteins titin and nebulin in postmortem aged beef, with known tenderness values, from animals differing in sex (steers vs bulls) and age (cows vs steers and bulls). Ten bulls and 10 steers (both groups were approximately 14 mo old) and 10 cows (44 to 108 mo old) were slaughtered. Longissimus muscle samples were removed for determination of Warner-Bratzler shear force, sensory panel tenderness evaluation, and SDS-PAGE analysis at 3, 7, 14, and 28 d postmortem. The SDS-PAGE analysis of titin and nebulin revealed that titin often migrated as three closelyspaced bands (T1, T1-2, T2, in increasing order of migration) in 3-d postmortem samples. With increasing time post-mortem, intact titin (T1) decreased and degraded titin (T2) increased in all samples. Within a class (i.e., steers, bulls, or cows) the rate of conversion of T1 to T2 was slower in the less-tender samples. The T1 to T2 conversion postmortem was slower in the intact males (bulls) than in the castrated males (steers). The T1 to T2 conversion postmortem also was slower in the older animals (cows) in comparison to the younger steers, but not in comparison to the younger bulls. Nebulin was degraded by 3 d postmortem in tender samples from steers, but some nebulin remained in the less-tender 3-d samples from steers and in all of the 3-d samples from bulls and older animals (cows). Intact nebulin was absent in all 7-d samples, regardless of the class of animal. Our results suggest that titin and nebulin are degraded at faster rates in more tender beef samples within each of the three classes of animals examined. The rate of degradation seems to differ when sex and age classifications are compared. The online version of this article, along with updated information and services, is located on ABSTRACT: This study was conducted to determine degradation of the giant myofibrillar proteins titin and nebulin in postmortem aged beef, with known tenderness values, from animals differing in sex (steers vs bulls) and age (cows vs steers and bulls). Ten bulls and 10 steers (both groups were approximately 14 mo old) and 10 cows (44 to 108 mo old) were slaughtered. Longissimus muscle samples were removed for determination of Warner-Bratzler shear force, sensory panel tenderness evaluation, and SDS-PAGE analysis at 3, 7, 14, and 28 d postmortem.The SDS-PAGE analysis of titin and nebulin revealed that titin often migrated as three closely-spaced bands ( T I , TI-2, T2, in increasing order of migration) in 3-d postmortem samples. With increasing time postmortem, intact titin ( T I ) decreased and degraded titin (T2) increased in all samples. Within a class (i.e., steers, bulls, or cows) the rate of conversion of TI t o T2 was slower in the less-tender samples. The TI to T2 conversion postmortem was slower in the intact males (bulls) than in the castrated males (steers). The T1 to T2 conversion postmortem also was slower in the older animals (cows) in comparison to the younger steers, but not ...