Toughness development in beef sternomandibularis muscle during cooking has been measured by a tenderometer, cleaving samples at right angles to the fibre direction. Since the muscles had been set in rigor mortis in an unshortened state, such toughening was not related to that induced by pre-rigor contraction.Two distinctly separate phases of toughening develop with increasing cooking temperature. A three-to fourfold toughening occurs in the first cooking phase between 40 and 50 "C, followed by a further doubling in the second phase between 65 and 75 "C. The first phase is associated with loss of myosin solubility, presumed to indicate denaturation in the contractile system. The second is closely associated with collagen shrinkage. This apparently induces shortening along the meat fibre, forcing out meat juice.

SUMMARY— During the aging of fiber pieces prepared from bovine sternomandibularis muscles, a loss of adhesion occurs between adjacent myofibrils. This is evidenced by increased readiness of fiber pieces to distintegrate into individual myofibrils during a period of standard disruption. Alterations also appear within the myofibrils themselves in the regions of the Z lines, sometimes leading to the apparent dissolution of this structure. Ethylenediamine tetraacetate present in the suspensions during storage not only prevents these changes, but also preserves the refractory character of the fiber pieces. Meat aging is considered therefore to be due to disruption and possible dissolution of Z‐line material, leading to a weakening of inter‐myofibrillar linkages probably located at the junctions of adjacent Z lines, and to loss of tensile strength of the myofibrils themselves.

No abstract

SUMMARY The proteolytic changes which occur in the longissimus dorsi muscles of beef carcasses during 30 days' aging at 2°C give rise to a mean increase of nonprotein nitrogen of 0.045mM/g meat, representing a degradation of 2.3% of the meat protein. The tenderizing and proteolysis which occur during aging are not related, for differences in the rates of tenderizing among carcasses arc not paralleled by similar differences in the rates of proteolysis. Bacterial action is not responsible for the observed proteolytic and tenderizing changes.

Shortening during the slow and rapid phases of rigor mortis onset determines largely the extent to which beef ages. For meat stored at 15°C for 3 days, shear-force values are uniformly low at shortenings of Oq/, to 20% of the freshly excised muscle length. However, there is a four-to five-fold increase in toughness as shortenings proceed from 20'>/, to 40%. This is followed by a decline in toughness as shortenings increase further from 40% to 55 yo. With increasing shortenings beyond 20%, progressive decreases occur in the extent to which meat ages until at 40% shortening, ageing has declined to zero.