Recipient Organization
OKLAHOMA STATE UNIVERSITY
(N/A)
STILLWATER,OK 74078
Performing Department
Animal Science
Non Technical Summary
Beef color is an important sensory property that influences consumers' purchasing decisions and the value assigned by USDA Graders. Consumers associate a characteristic bright-cherry red color with freshness and wholesomeness. Similarly, failure to have a bright-red color at the interface of 12th and 13th leads to discounted carcass value (no-roll) and meat that is typically not sold at retail.Dark-cutting beef is one of the most prominent meat quality issues worldwide. More specifically, the loss results from the price of beef carcasses during carcass grading. Therefore, characterizing the factors that contribute to dark-cutting beef is important to develop mitigation strategies and minimize losses associated with the occurrence of this defect.Previous research noted that dark-cutting and normal-pH longissimus lumborum muscles have different metabolite profiles. Meat discoloration is muscle-specific. For example, muscles predominant in Type I fibers are oxidative in nature and discolor faster than muscle predominant in glycolytic fiber types (Ke et al., 2017). Metabolite profiles of longissimus and psoas muscles are different in normal-pH muscles. However, no information is currently available on the metabolite profile differences between longissimus and psoas muscles from dark-cutting beef. The objectives were to determine color and biochemical properties of longissimus and psoas muscles from dark-cutting carcasses and characterize metabolite profiles using non-targeted gas chromatography-based mass spectrometry.
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
(N/A)
Goals / Objectives
The visual perception of meat color results from incident light properties. A greater-than-normal pH (5.6) can influence both muscle structural and biochemical properties. More specifically, a greater than normal pH promotes muscle fibers to hold water, leading to less reflectance and more absorption. In postmortem muscle, mitochondria remain active and influence meat color by oxygen consumption via utilization of tricarboxylic acid (TCA) cycle- and glycolytic-substrates/metabolites (Tang et al., 2005). In dark-cutting conditions, a greater than normal pH favors mitochondrial respiration. Dark-cutting beef has a greater mitochondrial number and oxygen consumption than normal-pH muscles (Ramanathan et al., 2020). The important role played by metabolites in meat color development has been well characterized. Previous research noted that dark-cutting and normal-pH longissimus lumborum muscles have different metabolite profiles (Ramanathan et al., 2020). Meat discoloration is muscle-specific. For example, muscles predominant in Type I fibers are oxidative in nature and discolor faster than muscle predominant in glycolytic fiber types (Ke et al., 2017). Metabolite profiles of longissimus and psoas muscles are different in normal-pH muscles (Abraham et al., 2017). However, no information is currently available on the metabolite profile differences between longissimus and psoas muscles from dark-cutting beef. The specific goals are:Determine color and biochemical properties of longissimus and psoas muscles from dark-cutting carcasses.Characterize metabolite profiles using non-targeted gas chromatography-based mass spectrometry.
Project Methods
Procedure: Raw material and sample allocation: Precautions will be taken during loin collection, transportation, and sample allocation as described by (McKeith et al., 2016). Normal-pH (approximate mean pH = 5.6) and dark-cutting beef (approximate mean pH > 6.4) longissimus lumborum and psoas major muscles from 10 carcasses will be collected 48 h postmortem or immediately after grading at a USDA approved packing plant (n = 10 for each muscle type; N = 20 total muscles from same breed and same age). Dark-cutting beef is usually identified by a USDA Grader in a beef plant based on longissimus color. Each muscle will be fabricated into six 1.91-cm thick steaks from the anterior end of the loin. Steaks from each pH class will be allocated to days 0, 2, 4, and 6. Steaks will be packaged using polyvinyl chloride over-wrap (the most common packaging) and will be displayed under retail conditions at 2°C. All precautions as described in AMSA guidelines (AMSA, 2012) will be taken during retail display and color measurements. The steaks assigned for shear force and taste panel will be stored at -20 °C until use.Color and pH measurements: Steak color will be measured using a HunterLab MiniScan XE Plus spectrophotometer (English et al., 2016). Both reflectance spectra from 400 to 700 nm (10 nm increments) and CIE L* and a* will be measured in triplicate for each steak, and subsamples will be averaged for statistical analyses. Reflectance at 525, 572, and 610 nm will be used to quantify the relative amounts of oxy- and metmyoglobin (AMSA, 2012). A greater L* and a* value indicate brighter red color. Also, pH will be recorded using a meat pH meter.Oxygen consumption of steaks: Postmortem oxygen consumption will be measured using a method similar to English et al. (2016). Deoxygenated beef steaks will be allowed to oxygenate at 1°C for 30 minutes. Samples will then be vacuum packaged, incubated at 4°C for 30 minutes, and the decrease in oxymyoglobin content will be used to assess oxygen consumption.Warner-Bratzler shear force measurement: Steaks will be thawed at 4°C for 24 h before cooking. Steaks will be broiled in an impingement oven at 180°C to an internal temperature of 70°C, and the internal temperature will be monitored using a thermocouple. After cooking, steaks will be allowed to cool to room temperature. A minimum of 6 cores (1.27-cm diam.) will be removed parallel to muscle fiber orientation. Core samples will be sheared once using a Warner-Bratzler head attached to an Instron Universal Testing Machine. Peak load (kg) of each core will be recorded by an IBM PS2 using software provided by the Instron Corporation. A lower shear force value is associated with tender meat.Sensory analyses: Steaks will be thawed in a refrigerator at 4 °C for 24 h, and will be cooked as previously described for Warner-Bratzler shear force determinations (Denzer et al., 2020). Sensory attributes will be evaluated by a 6-member trained panel. Using an eight-point scale, trained panelists will score samples for myofibrillar and overall tenderness, juiciness, flavor intensity, connective tissue amount, and off-flavor intensity (1=extremely tough, dry, bland, abundant, and intense; 8=extremely tender, juicy, intense, none, none). The panelists will be provided distilled, deionized water and unsalted crackers to cleanse their palate. Panelists will be verbally instructed to cleanse their palates between each sample.Lipid oxidation: Meat samples will be mixed with trichloroacetic acid, homogenized in a blender, and filtered using Whatman No. 1 filter paper as described by (Wills et al., 2017). One ml of filtrate will be mixed with 1 ml of 20 mM thiobarbituric acid and will incubate at 25 °C for 20 h. The absorbance at 532 nm will be reported as thiobarbituric acid reactive (TBAR) substances. The pH will be measured using a probe-type pH meter. A lower TBAR number indicates less lipid oxidation and is associated with improved color stability.Total plate count: The steaks will be analyzed for the total bacterial count (TPC) on d 6 of the simulated retail display according to the standard procedures for total plate count (37 °C, 48 h) on Petri film total plate agar (Mitacek et al., 2019). Ten grams of meat sample will be aseptically removed, homogenized in a stomacher, and then transferred to a test tube containing 9 ml of peptone water. Serial dilutions will be made by transferring 1 mL of extract from each dilution, and the samples will be inoculated in 3M™ Petrifilm™ Aerobic Count Plates. The colonies were counted after 48 h of incubation and expressed in log CFU/g.Metabolomic analysis: The methodology standardized by the P.I. will be used for metabolomics analysis (Abraham et al., 2017). Two grams of muscle tissue (in duplicates) from the interior of steak will be collected at different time points (0, 2, 4, and 6 days) from the normal-pH and dark-cutting beef and stored at -80°C. The metabolites will be then extracted by placing 500 mg of muscle tissue in 1.5 mL of methanol in a glass vial for 20 hours at room temperature (25°C). Ribitol will be added as an internal standard. Both samples will be dried under nitrogen, derivatized by adding MOX™ Reagent and BSTFA + 1% TMCS. Metabolites will be separated by gas chromatography and analyzed by mass spectrometry (GC/MS). Chromatography data will be analyzed using Chemstation software, and the spectra will be deconvoluted using AMDIS software. The compounds will be identified using the Fiehn metabolomics library and the NIST mass spectral library. Data will be analyzed using the Mass Profiler Professional Software for metabolomic studies.