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Functional properties and integrity of skeletal muscle mitochondria (mt) during the early postmortem period may influence energy metabolism and pH decline, thereby impacting meat quality development. Angus typically produce more tender beef than Brahman, a Bos indicus breed known for heat tolerance. Thus, our objectives were to compare mt respiratory function in muscle collected early postmortem (1 h) from Angus and Brahman steers (n = 26); and to evaluate the effect of normal and elevated temperature on mt function ex vivo. We measured mt oxygen consumption rate (OCR) in fresh-permeabilized muscle fibers from Longissimus lumborum (LL) at 2 temperatures (38.5 and 40.0 °C) and determined citrate synthase (CS) activity and expression of several mt proteins. The main effects of breed, temperature, and their interaction were tested for mt respiration, and breed effect was tested for CS activity and protein expression. Breed, but not temperature (P > 0.40), influenced mt OCR (per tissue weight), with Brahman exhibiting greater complex I+II-mediated oxidative phosphorylation capacity (P = 0.05). Complex I- and complex II-mediated OCR also tended to be greater in Brahman (P = 0.07 and P = 0.09, respectively). Activity of CS was higher in LL from Brahman compared to Angus (P = 0.05). Expression of specific mt proteins did not differ between breeds, except for higher expression of adenosine triphosphate (ATP) synthase subunit 5 alpha in Brahman muscle (P = 0.04). Coupling control ratio differed between breeds (P = 0.05), revealing greater coupling between oxygen consumption and phosphorylation in Brahman. Our data demonstrate that both Angus and Brahman mt retained functional capacity and integrity 1-h postmortem; greater oxidative phosphorylation capacity and coupling in Brahman mt could be related to heat tolerance and impact early postmortem metabolism.

Ultimate pH (pH u ) is an indicator that influences post-mortem meat quality. We studied physiological and biochemical changes of steaks obtained from Nellore bulls (Bos indicus) during post-mortem ageing. To this, Longissimus lumborum (LL) muscles were classified into three groups: Normal-pH u (≤5.79), Intermediate-pH u (5.80-6.29) and High-pH u (≥6.30) groups, portioned into steaks, vacuum packaged and matured at 2°C for 0, 7, 14, 21 and 28 days. High-pH u steaks exhibited impaired colour stability and were darker compared to the other groups. High-and Normal-pH u steaks showed improved tenderness and myofibrillar fragmentation linked to proteolysis. Intermediate-pH u steaks were associated with a lower meat tenderness and decreased collagen solubility. High-pH u steaks retained a high pH during ageing and increased water-holding capacity. These findings provide evidence that highlight pH u as a strategy for the classification of pH u -dependent beef quality from Nellore bulls that can be adopted by the Brazilian meat industry.

Meat quality is traditionally associated with anaerobic metabolism due to cessation of the oxygen supply post-mortem. However, mitochondrial (mt) function early postmortem may affect the development of meat quality characteristics, such as adenosine triphosphate levels and pH decline. Therefore, the objective of this study was to evaluate mt function ex vivo during the first 24 h postmortem in muscles with differences in mt content. Samples from longissimus lumborum (LL) and diaphragm (Dia) were taken from steers (n = 6) at 1, 3, and 24 h postmortem and frozen to determine citrate synthase (CS) activity and mt protein expression (immunodetection) or were fresh-preserved for high-resolution respirometry. Integrative oxygen consumption rate (picomoles per second per milligram of tissue) was measured and normalized to CS activity as a proxy for mt content (intrinsic mt function, picomoles per second per unit CS). CS activity (P < 0.001) and mt protein expression (P < 0.001) were greater in Dia, which was reflected in mt respiration. Muscle type affected (P < 0.001) integrative leak respiration and was greater in mt from Dia; oxidative phosphorylation (OXPHOS) was also greater in Dia and influenced by time postmortem (muscle × time: P = 0.01). Intrinsic leak and OXPHOS were affected by muscle and time (muscle × time: P = 0.05 and P = 0.01, respectively), with the most pronounced differences at 24 h postmortem. Stimulation of OXPHOS by cytochrome c as an indicator of outer mt membrane integrity was influenced by muscle and time postmortem (muscle × time: P = 0.03); it was greater in mt from LL. Despite intrinsic differences in respiratory function at 24 h, mt from both muscles were intact and coupled at 1 h postmortem. Reduced content and respiratory function in mt from LL are associated with early fragmentation, which could impact protease activation and subsequently meat quality.

SUMMARYThis study evaluates the effects of Normal Shortening (NS) and Cold Shortening (CS) in sarcomere length, Warner-Bratzler shear force (WBS) and tenderization process examined by Myofibrillar Fragmentation Index (MFI). The Biceps femoris muscle from ten Dorper x Santa Inês lambs was randomly assigned to 1) NS = cooling of the muscle in the carcass for 24 hours in a cold room at 4°C; or 2) CS = rapid cooling, in ice bath, of the muscle removed from the carcass immediately after slaughter. Sarcomere Length (SL) was determined in the collected samples 24 hours after slaughter and WBS and MFI in the aging periods (1 or 10 days post-mortem). The WBS value of the meat for 1 and 10 days were greater (P<0.05) for CS (4.90 ± 0.42 and 3.73 ± 0.42 kgf, respectively) than NS (4.07 ± 0.36 and 2.98 ± 0.38 kgf, respectively). There were negative correlations between WBS and SL (r= -0.59 and r=-0.69, P< 0.05) at 1 and 10 postmortem, respectively. Furthermore, there were positive correlations for MFI and SL (r= 0.46 and r=0.48, P< 0.05) at days 1 and 10, respectively. These results point to a negative impact of sarcomere cold shortening in the sheep meat tenderization process in the hindlimb muscle.Keywords: shear force, myofibrillar, proteolysis, meat, Santa Inês RESUMOForam avaliados os efeitos do encurtamento normal (NS) e encurtamento pelo frio (CS) no comprimento do sarcômero, força de cisalhamento pelo WarnerBratzler (WBS) e no processo de amaciamento analisado pelo índice de fragmentação miofibrilar (MFI). Os músculos Bicep femoris de dez ovinos oriundos do cruzamento Dorper x Santa Inês, foram aleatoriamente designados para: 1) NS: resfriamento do músculo na carcaça por 24 horas na câmara fria a 4°C (NS) 2) CS: resfriamento rápido, em banho de gelo, do músculo removido a partir da carcaça imediatamente após o abate (CS). Comprimento de sarcômero foi determinado nas amostras coletadas 24 horas após o abate e WBS e MFI nos períodos de maturação (1 ou 10 post mortem), em cada tratamento. Os valores de WBS da carne para 1 e 10 dias foram maiores (P <0,05) para CS (4,90 ± 0,42 e 3,73 ± 0,42 kgf, respectivamente) que para NS (4,07 ± 0,36 e 2,98 ± 0,38 kgf, respectivamente). Houve correlação negativa para WBS e comprimento do sarcômero (r = -0,59 e r = -0,69, P <0,05) nos dias 1 e 10 de post-mortem. Além disso, foram observadas correlações positivas entre MFI e comprimento do sarcômero (r = 0,46 e r = 0,48, P <0,05) nos dias 1 e 10, respectivamente. Esses resultados apontam para um impacto negativo do encurtamento do sarcômero no processo de amaciamento de carne em músculo do pernil de cordeiros. Palavras-chave:força de cisalhamento, miofibrilar, proteólise, carne, Santa Inês Rev.