Morgan D. Zumbaugh

This erratum corrects the title and the description of the thawing systems used in the experiment for “Effect of Electromagnetic Field Assisted Thawing on the Quality of Previously Frozen Beef Striploins.”

Wooden breast (WB) is a myopathy that occurs in pectoralis major (PM) muscles, predominately affecting large, fast-growing broilers. Severe myodegeneration, increased hypoxia, reduced blood flow, and increased collagen deposition are hallmark characteristics of WB that culminate in unsatisfactory fresh meat quality attributes, such as poor water-holding capacity, tenderness, and processing characteristics. Therefore, WB meat is often downgraded resulting in economic losses for the United States poultry industry. Although WB has been well characterized, its etiology remains undefined. As the scientific community continues to resolve mechanisms responsible for WB onset, understanding biochemical changes associated with WB may facilitate solutions to negate its poor meat quality attributes. Given changes in metabolism of living muscle can alter biochemical processes during the conversion of muscle to meat, this review aims to summarize and discuss the current knowledge of WB muscle and meat biochemistry. For example, it appears metabolic pathways that support combating stress are upregulated in WB muscle at the expense of glycolytic flux, which presumably contributes to the high ultimate pH of WB meat. Further, perturbed function of WB mitochondria, such as altered calcium handling, impacts aspects of postmortem metabolism and proteolysis. Collectively, metabolic dysfunction of WB muscle alters the biochemical processes that occur during the conversion of muscle to meat, and thus contributes to the poor WB meat quality.

Background: Mitochondria are considered the powerhouse of cells, and skeletal muscle cells are no exception. However, information regarding muscle mitochondria from different species is limited. Methods: Different muscles from cattle, pigs and chickens were analyzed for mitochondrial DNA (mtDNA), protein and oxygen consumption. Results: Bovine oxidative muscle mitochondria contain greater mtDNA (p < 0.05), protein (succinate dehydrogenase, SDHA, p < 0.01; citrate synthase, CS, p < 0.01; complex I, CI, p < 0.05), and oxygen consumption (p < 0.01) than their glycolytic counterpart. Likewise, porcine oxidative muscle contains greater mtDNA (p < 0.01), mitochondrial proteins (SDHA, p < 0.05; CS, p < 0.001; CI, p < 0.01) and oxidative phosphorylation capacity (OXPHOS, p < 0.05) in comparison to glycolytic muscle. However, avian oxidative skeletal muscle showed no differences in absolute mtDNA, SDHA, CI, complex II, lactate dehydrogenase, or glyceraldehyde 3 phosphate dehydrogenase compared to their glycolytic counterpart. Even so, avian mitochondria isolated from oxidative muscles had greater OXPHOS capacity (p < 0.05) than glycolytic muscle. Conclusions: These data show avian mitochondria function is independent of absolute mtDNA content and protein abundance, and argue that multiple levels of inquiry are warranted to determine the wholistic role of mitochondria in skeletal muscle.

Skeletal muscle metabolism has implications for swine feed efficiency (FE); however, it remains unclear if the metabolic profile of skeletal muscle changes during postnatal growth. To assess the metabolic changes, samples were collected from the longissimus dorsi (LD, glycolytic muscle), latissimus dorsi (LAT, mixed muscle), and masseter (MS, oxidative muscle) at 20, 53, 87, 120, and 180 days of age from barrows. Muscles were assessed to determine the abundance of several metabolic enzymes. Lactate dehydrogenase (LDHα) decreased in all muscles from 20 to 87 d (p < 0.01), which may be attributed to the muscles being more glycolytic at weaning from a milk-based diet. Pyruvate carboxylase (PC) increased in all muscles at 53 d compared to the other time points (p < 0.01), while pyruvate dehydrogenase α 1 (PDHα1) increased at 87 and 180 d in MS compared to LD (p < 0.05), indicating that potential changes occur in pyruvate entry into the tricarboxylic acid (TCA) cycle during growth. Isolated mitochondria from each muscle were incubated with ¹³C-labeled metabolites to assess isotopomer enrichment patterns of TCA intermediates. Citrate M + 2 and M + 4 derived from [¹³C₃]-pyruvate increased at 87 d in LAT and MS mitochondria compared to LD mitochondria (p < 0.05). Regardless of the muscle, citrate M+3 increased at 87 d compared to 20, 53, and 120 d, while 180 d showed intermediate values (p < 0.01). These data support the notion that pyruvate metabolism is dynamic during growth. Our findings establish a metabolic fingerprint associated with postnatal muscle hypertrophy.

The objective of this study was to evaluate the impact of applying electrostatic field (EF)–assisted thawing on the quality attributes of previously frozen beef striploin. Beef striploins from both sides of 12 USDA Choice carcasses were halved, frozen at −40°C, and thawed under 4 EF voltage treatments: 0 kV (control), 2.5 kV, 5 kV, and 10 kV. After reaching the internal temperature of −1°C, striploins were weighed for yield calculation, swabbed for microbial analysis, fabricated into steaks, and assigned to either 0- or 14-d aging period and retail displayed for 0 or 7 d. Subjective and objective color measurements were taken during the retail display. Upon completion of retail display, Warner-Bratzler shear force (WBSF), cook loss, sarcomere length, troponin-T degradation, muscle fiber spacing, lipid oxidation, antioxidant capacity, pH, and proximate analysis were performed. All EF treatments increased purge loss compared to the control (P<0.05) and did not improve thawing speed, with samples from 10 kV actually taking the longest to thaw (P<0.05). The 2.5 kV and 5 kV samples aged 14 d showed less discoloration than those from 0 kV and 10 kV, and 5 kV samples aged 14 d had higher a* than those from the other treatments (P<0.05). Samples thawed under 10 kV showed a reduction in WBSF compared to the control (P0.05). Overall, our study determined that there was no economic benefit to apply EF during thawing regarding yield and purge loss. However, the application of EF may improve tenderness and extend shelf life of beef during retail display.

Although studies evaluating freezing are prevalent, most have used varied postmortem aging times to facilitate study design. The lack of a comprehensive study evaluating equally aged fresh and frozen steaks prevents a true under-standing of the impact of freezing. Therefore, the objective of this study was to determine the eating quality and consumer perception differences between fresh and frozen beef steaks of 3 equal aging periods. Beef carcasses were selected from a processing plant on 2 kill dates 1 wk apart to allow for a 1-wk freezing period, fabricated, and aged for 21, 28, or 35 d. On the same day, all samples of equal aging periods were fed to consumer and trained sensory panelists, sheared for shear force, and powdered for lab assays. For consumer panels, the first 4 steaks were given with no additional information, whereas the last 4 steaks were served with the labels “previously frozen” or “fresh, never frozen.” The consumer panelists rated the frozen samples as more tender (P0.05). Even when given additional information, the perception of quality was not impacted (P>0.05). Similarly, the trained panelists rated the frozen samples higher (P<0.05) than the fresh counterparts for overall tenderness, but the fresh samples scored higher (P<0.05) for initial and sustained juiciness. Supporting the sensory data, the frozen steaks had lower (P<0.05) shear force values regardless of the aging period. However, the fresh samples resulted in lower (P<0.05) purge and cook loss. Although some meat quality factors were impacted by freezing, the overall eating quality and perception of quality were not negatively impacted. Therefore, frozen meat should not be discounted due to the eating quality or perception of the quality of beef steaks.

The objective of this study was to evaluate the palatability of 3 plant-based ground beef alternatives (GBA) in comparison to ground beef under real-world hamburger and taco scenarios. The 3 plant-based GBA alternatives used represented a modern GBA sold at retail (RGBA), a modern GBA sold in foodservice (FGBA), and a traditional soy-based GBA (TGBA). Additionally, 80% lean ground beef was evaluated. Consumers (N=240; n=120 per panel type) evaluated samples for juiciness, tenderness, texture, beef flavor, overall flavor, overall liking, purchase intent,and purchase price and rated traits as either acceptable or unacceptable. For hamburger panels, consumers were served samples on buns and were given the option to add cheese, lettuce, pickles, ketchup, and/or mustard. For taco panels, samples were seasoned with a taco seasoning blend and served on flour tortillas, with consumers given the option to add cheese, lettuce, and/or tomatoes. In both scenarios, ground beef was rated higher (P0.05) for tenderness to FGBA and RGBA. Additionally, a higher (P<0.05) percentage of ground beef samples were rated acceptable overall and for flavor characteristics than all 3 GBA. Few differences were found between FGBA and RGBA for any palatability characteristics evaluated. TGBA was rated lower (P0.05) to only RGBA for beef flavor and overall flavor liking within hamburger panels. These results indicate that GBA currently available to consumers do not have improved palatability characteristics when used as an ingredient in a taco or hamburger scenario.

Variations in postmortem metabolism in muscle impact pork quality development. Curiously, some genetic lines are more refractile to adverse pork quality development than others and may regulate energy metabolism differently. The aim of this study was to challenge pork carcasses from different genetic populations with electrical stimulation (ES) to determine how postmortem metabolism varies with genetic line and explore control points that reside in glycolysis in dying muscle. Three genetic populations (GP) were subjected to ES (100 V or 200 V, 13 pulses, 2 s on/2 s off) at 15- or 25-min post-exsanguination, or no stimulation (NS). Genetic population affected relative muscle relative abundance of different myosin heavy chains, glycogen, G6P, and lactate concentrations. Genetic lines responded similarly to ES, but a comparison of ES treatment groups revealed a trend for an interaction between voltage, time of ES, and time postmortem. Higher voltage accelerated pH decline at 20 min up to 60 min postmortem. Trends in color and firmness scores and L* values were consistent with pH and metabolite data. These data show that genetic populations respond differently to postmortem perturbation by altering glycolytic flux and suggest differences in postmortem glycolysis may be partially responsible for differences in meat quality between genetic populations, though not entirely.