SUMMARY Interrelationships of fiber diameter, sarcomere length, and tenderness were studied in 12 bovine muscles of horizontally placed and vertically suspended carcass sides. In comparison with the horizontally placed sides, the vertically suspended sides had greater sarcomere lengths in the psoas major, latissimus dorsi, and rectus femoris muscles. Conversely, vertical suspension permitted the longissimus dorsi, gluteus medius, adductor, biceps femoris, and semitendinosus muscles to shorten in sarcomere length. In general the differences in sareomere lengths of muscles (between sides) were associated (r=–.82 P <.01) with differences in fiber diameter. Differences in fiber diameter (between sides) were highly related to differences in shear force (r= .73, P <.01, as were differences in sarcomere length (T = ‐.80, P <.01). When museles shortened, there were corresponding decreases in sarcomere length, increases in fiber diameter, and decreases in tenderness.

Tenderness of semitendinosus and psoas major bovine muscles was markedly affected by: ( I ) allowing the muscle to undergo rigor mortis and the associated contraction, following pre-rigor excision, or by ( 2 ) pre-rigor excision followed by restraint in a stretched state while the muscle undergoes rigor mortis. The extent of stretch or contraction induced by pre-rigor treatment was reflected by the sarcomere length. The average sarcomere length of the semitendinosus and psoas major muscles differed widely when samples were removed post-rigor from the carcass. The data indicate that the state of contraction (measured by sarcomere length), when altered in different portions of the same muscle by treatment, or when varying naturally in different muscles, was associated with tenderness. IntroductionNumerous studies have been conducted during the past few years to determine the specific contribution of various factors to the tenderness of bovine muscle.l-12 One of the factors reported has been the difference in contraction state of myofibrils in bovine m~sc1es.l~ This worker postulated that the variations in sarcomere lengths among muscles, were due, in part, to the strains induced in the muscles when the carcass was vertically suspended, and also that since long sarcomeres occurred in muscles previously reported14 to be generally tender, the state of contraction was considered a factor contributing to tenderness, where the effect of connective tissue was small.Herring & Briskey5 noted that portions of bovine semitendinosus muscle, excised pre-rigor and stretched during cooking, were tender, while similar portions from the same muscle, excised and cooked in the free unrestrained state, shortened markedly and were tough.The present study was conducted in order to expand on the above general problem of tenderness and specifically to investigate further the report of Locker'3 which implicated muscular contraction in the problem of tenderness. Studies were made on different portions of the same muscle which were allowed to undergo rigor mortis under different experimental conditions in order to determine the relationships among contraction state, sarcomere length and tenderness.

SUMMARY— Solubility of intramuscular collagen was studied as affected by chronological maturity in 15 bovine longissimus dorsi and 15 semimembranosus muscles and as affected by post‐mortem contraction state in the semitendinosus of 7 animals. Collagen solubility decreased significantly with each advancing maturity group in both longissimus dorsi and semimembranosus muscles. Collagen solubility was also higher (P < 0.05) in the longissimus dorsi than in the semimembranosus, except in the E maturity group. It was also related to panel tenderness in both muscles (r = 0.77 and 0.81 (P < 0.01) for longissimus dorsi and semimembranosus muscles, respectively. However, within‐maturity group correlations of solubility of collagen and tenderness were low and nonsignificent. Collagen content did not differ significantly in longissimus dorsi muscles of animals of A, B, and E maturity groups; however, the semimembranosus had more collagen (P < 0.05) in E than in A and B maturity groups. Collagen content was not related (P > 0.05) to panel tenderness in either muscle (r =−0.42 and −0.48 for longissimus dorsi and semimembranosus, respectively). Neither collagen solubility nor collagen content was significantly affected by post‐mortem contraction state. Furthermore, collagen solubility did not increase significantly with post‐mortem aging up to ten days.

SUMMARY— The effects of muscle contraction state, carcass maturity, and post‐mortem aging (4°C) on tenderness were studied on excised semitendinosus muscles of six A‐ and six E‐maturity bovine carcasses. Fiber diameter was shown to be curvilinearly related with sarcomere length (R = .95 and .87 for A‐ and E‐maturity groups, respectively). As muscles were shortened they had a larger percent area of fibers and a smaller percent area of both edomysial and perimysial material. Muscles of the A‐maturity group were more tender (P < .01) than those of the E‐maturity group. Post‐mortem aging resulted in tenderization in both A‐ and E‐maturity groups at all states of contraction f‐48 to +48% of the preexcised length); however, tenderness of contracted muscles did not reach acceptable levels even in 240 hr of aging. Tenderness was shown to be linearly related to fiber diameter (R = .82 and .87 for A‐ and E‐maturity groups, respectively); however, the relationship with sarcomere length was curvilinear (R = .90 and .75 for A and E maturities, respectively). Post‐mortem contraction of muscles was very effective in causing decreased tenderness, whereas the magnitude of tenderness increase was smaller than normal when muscles were stretched.

No abstract