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Anaerobic glycolysis dominates energy metabolism postmortem. Even so, however, recent studies suggest mitochondria can modify postmortem energy metabolism and may contribute to pH decline, possibly affecting the transformation of muscle to meat and fresh meat quality development. Because oxygen is a necessary component of mitochondrial function, oxygenation of porcine and bovine longissimus thoracis et lumborum was determined postmortem using NIR spectroscopy. The ratio of oxy- to deoxymyoglobin decreased with time postmortem in both species. Metabolic analyses of muscle samples collected over the same timeframe also revealed fluctuations in TCA intermediates. Finally, mitochondria collected from muscle of electrically stimulated carcasses differed from those of non-stimulated muscle. Collectively, these data support the thesis that muscle mitochondria function early postmortem and may play a more active part in pH decline and possibly meat quality development.

The experiment was conducted to identify the mitochondrial protein responsible for enhancing glycolytic flux. We hypothesized that mitochondrial F1-ATPase promotes ATP hydrolysis and thereby the flux through glycolysis. Porcine longissimus muscle mitochondria were incorporated into an in vitro system designed to recapitulate postmortem glycolysis with or without Na-azide to specifically inhibit the β-subunit of mitochondrial F1-ATPase that catalyzes ATP hydrolysis. Addition of mitochondria enhanced ATP hydrolysis, glycogen degradation, lactate accumulation, and pH decline in the in vitro system. However, the majority of mitochondria-mediated enhancement in glycolytic flux was abolished in the presence of Na-azide. To investigate further, myofibrillar and mitochondrial proteins were added to the in vitro system after 240min from the initiation of the reaction. Greater pH decline and lactate accumulation were observed in system containing mitochondrial protein compared to their myofibrillar counterpart. In conclusion, mitochondrial F1-ATPase is capable of increasing glycolytic flux through promoting greater ATP hydrolysis at lower pH.

Fresh hams display significant lean color variation that persists through further processing and contributes to a less desirable cured product. In an attempt to understand the underlying cause of this color disparity, we evaluated the differences in muscle characteristics and energy metabolites across semimembranosus (SM) muscles differing in color variation. The L* (lightness) and a* (redness) values were highest and lowest (P

Fresh turkey meat color is determined by many factors that include muscle fiber type composition and heme protein concentrations. These factors either are affected by or influence biochemical events occurring postmortem. Deviations in the processing environment also can result in aberrant fresh meat quality and may ultimately change the quality characteristics of further processed products. Our objective was to describe the underlying cause and significance of the two-toning color defect in fresh turkey breast. In the first experiment, pectoralis major muscles were collected, classified as single- or two-toned, and analyzed using image processing to characterize fresh turkey color. Samples from the large and small lobes of the pectoralis major muscle were collected for pH, glycolytic intermediates, protein abundance, mRNA expression, and quality characteristics. In the second experiment, time from stun to exsanguination was tested as a promoter of fresh turkey color. Results from the first experiment showed that the turkey breast possesses two distinct lobes. The large lobe had greater (P 0.05) glycolytic potential, lactate content, lactate dehydrogenase (LDH) abundance, and centrifugal drip loss, while pH, myoglobin mRNA expression, and soluble protein levels were lower (P 0.05) compared to the small lobe. Results from the second experiment showed that reducing time from stun to exsanguination enhanced (P 0.05) fresh turkey color by mitigating the differences between the two lobes. Our results also showed that birds exsanguinated first had greater (P 0.05) muscle pH values and body temperatures. These results show inherent differences in breast muscle and processing conditions interact to establish variations in fresh turkey color.

Our objective was to evaluate the efficacy of Color Muse and Nix Pro 2 colorimeters in measuring food color. To that end, measured color coordinates (L*, a*, b*, C*, and h*) of vegetables, fruits, cheeses, and meats by Color Muse and Nix Pro 2 were compared to values obtained with a Minolta CR-400 colorimeter. In general, color space values obtained with Color Muse were greater than those of CR-400 and Nix Pro 2 (P 90%). Taken together, our data suggest that Color Muse and Nix Pro 2 are reliable instruments that can be utilized as alternatives to high-cost colorimeters in food color research.

The purpose of this study was to test mitochondrial functionality under conditions simulating postmortem metabolism. Isolated mitochondria from porcine longissimus lumborum (LLM) and masseter (MM) muscles were incorporated into an in vitro model that mimics postmortem metabolism. pH and 13C-enrichment of glycolytic and tricarboxylic acid (TCA) cycle intermediates were evaluated at 0, 15, 30, 120, 240, and 1440 min. Addition of mitochondria to the in vitro model lowered its pH at 240 min compared with control. Reactions containing mitochondria had lower pyruvate and lactate [M + 2] and [M + 3] isotopomers at 240 and 1440 min than controls. Furthermore, LLM lowered the enrichment of [M + 2], [M + 3], and [M + 4]α-ketoglutarate at 1440 min compared with MM and control. Succinate [M + 2] and [M + 3] were greater in MM than the control and LLM. [M + 3]fumarate was greater in control at 240 and 1440 min than LLM and MM treatments. Our data indicated that mitochondria are capable of mobilizing pyruvate generated though glycolysis under conditions simulating muscle postmortem metabolism.

Animal selection based on growth rate has received greater attention as a selection index. While many have evaluated the effect of growth rate on muscle characteristics and meat quality, few studies have attempted to evaluate how selection based on growth rate alters muscle fiber characteristics and influences postmortem metabolism and subsequent meat quality. Therefore, the objective of this study was to evaluate muscle fiber type, postmortem metabolism and meat quality of Nellore cattle selected for different growth rates. Two-hundred and fifty non-castrated Nellore males differing in post-weaning growth potentials were used. Muscle from 10 high growth potential animals (EPDH) and 10 low growth potential animals (EPDL) were analyzed for muscle morphometric profile, postmortem metabolism, and meat quality. EPDH animals were heavier and had higher hot carcass weight and larger diameter and cross-sectional area of fast oxidative-glycolytic fibers, while EPDL animals had higher area percentage of slow oxidative fibers. Moreover, EPDH presented higher glycogen concentrations than EPDL cattle. Glucose concentrations were higher at 240, 720, and 1440 min postmortem, while G6P was higher from 30 to 1440 min postmortem in EPDL animals. Finally, EPDH animals produced less tender meat when compared to that of EPDL cattle. In conclusion, genetic selection based on growth potential is associate with a shift in fiber type towards a more glycolytic type of muscle that is associated with changes in meat tenderness.

Skeletal muscle glycogen content can impact the extent of postmortem pH decline. Compared to glycolytic muscles, oxidative muscles contain lower glycogen levels antemortem which may contribute to the higher ultimate pH. In an effort to explore further the participation of glycogen in postmortem metabolism, we postulated that increasing the availability of glycogen would drive additional pH decline in oxidative muscles to equivalent pH values similar to the ultimate pH of glycolytic muscles. Glycolysis and pH declines were compared in porcine longissimus lumborum (glycolytic) and masseter (oxidative) muscles using an in vitro system in the presence of excess glycogen. The ultimate pH of the system containing longissimus lumborum reached a value similar to that observed in intact muscle. The pH decline of the system containing masseter samples stopped prematurely resulting in a higher ultimate pH which was similar to that of intact masseter muscle. To investigate further, we titrated powdered longissimus lumborum and masseter samples in the reaction buffer. As the percentage of glycolytic sample increased, the ultimate pH decreased. These data show that oxidative muscle produces meat with a high ultimate pH regardless of glycogen content and suggest that inherent muscle factors associated with glycolytic muscle control the extent of pH decline in pig muscles.

The purpose of this study was to examine the role of mitochondria in postmortem calcium homeostasis and its effect on proteolysis and tenderness. We hypothesized that mitochondria buffer cytosolic calcium levels and delay the activation of calpain-1 and subsequently the development of meat tenderness. To test this hypothesis, pre-rigor bovine longissimus thoracis et lumborum muscle samples were injected with DS16570511 to inhibit mitochondrial calcium uptake. Free calcium, tenderness, texture profile analysis (TPA), calpain-1 activity, and proteolysis were evaluated over a 336 h aging period. Inhibition of mitochondrial calcium uptake increased (P

Postmortem lactate accumulation in skeletal muscle is linearly associated with the extent of pH decline. Yet, pigs harboring the AMPKγ3(R200Q) mutation produce meat with similar lactate levels to that of wild-type pigs but have a lower ultimate pH. We hypothesized that lower initial lactate levels and (or) lower buffering capacity in muscle of these pigs may help explain this discrepancy. Longissimus lumborum muscle samples were harvested at 0 and 1440 min postmortem from AMPKγ3(R200Q) and wild-type pigs. As expected, AMPKγ3(R200Q) muscle exhibited a lower ultimate pH but similar lactate levels to that of wild-type pigs at 1440 min postmortem. However, the total net lactate produced postmortem was greater in the AMPKγ3(R200Q) muscle due to lower initial lactate levels at 0 min postmortem. Buffering capacity measured over the pH range of 5.5-7.0 was also lower in AMPKγ3(R200Q) muscle. Greater net lactate accumulation postmortem (i.e., glycolytic flux) coupled with a lower buffering capacity explains the lower ultimate pH of meat from AMPKγ3(R200Q) pigs.

Our objective was to determine the influence of mitochondria on metabolites and pH decline using an in vitro model of postmortem muscle metabolism. Mitochondria were isolated from porcine longissimus lumborum and added (0, 0.5, or 2.0 mg) to powdered muscle in reaction media containing either a combination of inhibitors for mitochondria complexes (I, IV, and V) or diluent (without inhibitors). In the absence of inhibitors, adding mitochondria (0.5 and 2.0 mg) reduced ATP loss from 30 to 120 min, but did not alter glycogen or lactate during this time. In reactions with mitochondria, inhibitors decreased ATP levels by 30 min and increased glycogen degradation by 60 min. Regardless of mitochondria content, inhibitors enhanced lactate accumulation from 15 to 240 min, and decreased pH from 15 min to 1440 min. In the in vitro model, mitochondria influence the maintenance of ATP, and inhibition of mitochondria enzyme activity contributes to accelerated metabolism and pH decline.

Fresh meat quality development is influenced by pH decline that results from muscle glycolyzing energy substrates postmortem. The exact reason why glycolysis stops in the presence of residual glycogen remains unclear. We hypothesized that a critical glycolytic enzyme loses activity near the ultimate pH of meat. Porcine longissimus muscle samples were subjected to an in vitro system that mimics postmortem anaerobic metabolism at buffered pH values (7.0, 6.5, 6.0, 5.5 or 5.0). At pH7.0, 6.5, and 6.0, glycogenolysis and glycolysis proceeded normally while pH5.5 stopped lactate formation. Additional experimentation indicated that phosphofructokinase lost activity at pH5.5 while all other glycolytic enzymes remained active. A similar inactivation of phosphofructokinase was observed when using chicken and beef muscle. Elevated temperature hastened pH decline and phosphofructokinase activity loss. Thus, pH inactivates phosphofructokinase and arrests postmortem glycolysis, which may explain the similar ultimate pH across meat of different species.

Meat quality development, or the transformation of muscle to meat, involves a myriad of biochemical pathways that are largely well-studied in living muscle tissue. However, these pathways are less predictable when homeostatic ranges are violated. In addition, there is far less known about how various management or environmental stimuli impact these pathways, either by substrate load or altered cellular environment. Likewise, it is largely accepted that oxygen plays little to no role in the conversion of muscle to meat, as anaerobic metabolism predominates in the muscle tissue. Even so, the oxygen tension within the tissues does not fall precipitously at exsanguination. Therefore, transition to an anaerobic environment may impact energy metabolism postmortem. Antemortem handling, on the other hand, clearly impacts meat quality development, yet the exact mechanisms remain a mystery. In this paper, we will attempt to review those factors known to affect postmortem energy metabolism in muscle and explore those areas where additional work may be fruitful.

A 70-d experiment was conducted to evaluate the effect of feeding poultry broiler litter (BL) at levels 0 (BL0; n = 10), 100 (BL100; n = 10), and 200 g/kg (BL200; n = 10) on performance and carcass characteristics Awassi lambs. Nutrient intakes [i.e., dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (aNDF), acid detergent fiber (ADF), and copper] were similar (P>0.05) between all diets except for ether extract (EE) intake which tended to be lower (P≤0.10) for the BL20 diet than the BL0 diet whereas BL100 not different from the other two diets. Dry matter, OM, CP, aNDF, and ADF digestibility was lower (P 0.05) average daily gain (ADG) and dry matter intake (DMI):ADG. For dissected loin, intermuscular fat content was lower (P

SUMMARY The influence of carcass weight, bird sex, and carcass aging time on meat quality traits of pectoralis major muscles was studied in broiler birds. A total of 800 birds were used. After processing, carcasses were graded into 3 categories: 1,500 to 1,600 g, 1,600 to 1,700 g, and greater than 1,700 g. Forty-two carcasses from broilers of each sex were randomly selected from each carcass weight category. Seven carcasses of broilers from each sex within the same carcass weight category were aged for 0, 2, 4, 6, 8, and 24 h postchilling. The ADG and FCR increased (P 0.05) by any of the factors. Cooking loss was affected only by bird sex. Lighter carcasses had a higher (P