Location: Meat Safety and Quality
Project Number: 3040-31430-006-011-T
Project Type: Trust Fund Cooperative Agreement
Start Date: May 1, 2020
End Date: Nov 30, 2021
We hypothesize that increased mitochondrial abundance and decreased mitochondrial efficiency is associated with decreased glycogen at death, which will increase ultimate postmortem pH. Carcasses with higher ultimate pH (but still considered normal in lean color) have increased toughness and decreased color stability. Additionally, biomarkers will facilitate understanding the underlying biochemistry affecting tenderness and color stability. Thus, our specific objectives are: 1. Determine the nature of relationships between metabolic factors and palatability and consumer appeal across the range of pH represented in the U.S. beef trade. 2. Evaluate the contribution of mitochondrial abundance and mitochondrial efficiency to muscle pH and variation in beef palatability and color traits in carcasses with intermediate ultimate pH values. 3. Validate metabolic biomarkers for beef palatability and consumer appeal on an independent population and provide insight into the mechanisms by which they influence beef flavor, tenderness, and color.
Beef carcasses (n = 100) will be selected on 5 selection days from a large commercial processing facility. Carcasses that are identified as dark cutters by plant personnel using visual or camera determination will be excluded from the experiment and carcasses will represent the U.S. Choice and Select grades. Muscle pH will be determined using a portable pH meter and muscle probe calibrated according to manufacturer’s instructions in the posterior surface of the longissimus lumborum exposed by ribbing the carcass at the 12th – 13th rib interface for grading. Carcasses will be selected to represent 4 pH classes (n = 25 per class): < 5.6, 5.60 to 5.74, 5.75 to 5.9, and > 5.9. Left striploins will be obtained and transported to USMARC. Strip loins will be aged until 14d postmortem and cut into 28-mm-thick steaks. The first two steaks will be used for trained sensory panel analysis, for tenderness, juiciness, and flavor attributes. The third steak will be utilized to determine slice shear force. The fourth steak will be utilized for biochemical measurements. The fifth steak will be utilized for simulated retail display. The sixth steak will be utilized to determine oxygen consumption and metmyoglobin reducing ability. Highly trained and experienced sensory panelists will evaluate sensory steaks for descriptive tenderness, juiciness, and flavor analysis. Panelists will be trained on descriptive attributes (tenderness and juiciness) according to the methods described by the American Meat Science Association (AMSA, 2016) and the Beef Flavor Lexicon developed by Adhikari et al. (2011) for descriptive flavor attributes. Slice shear force will be determined on the cooked steaks as described by Shackelford et al. (1999). The cooked and sheared slices will be pulverized in liquid nitrogen and used for biochemical measurements of sarcomere length and desmin degradation through western blotting as described by Wheeler et al. (2002). Application Summary Color stability of retail display steaks will be measured as described by McKeith et al. (2016)at 0, 1, 4, 7, and 11 d of display. Oxygen consumption and nitric oxide reducing ability will be measured as described by AMSA (2012). Myoglobin concentration and muscle pH will be determined using a modification of the method reported by AMSA (2012). The extract used for myoglobin determination also will be used with a Quantichrom TBARS Assay kit (BioAssay Systems, Haward, CA) to measure lipid oxidation. Glycolytic potential determination will be conducted following the procedure of (Souza et al., 2011) as modified by McKeith et al. (2016) with the additional modification that glucose, glucose-6-phoshpate, and glycogen will be quantified separately. Moreover, malic acid will be quantified using a colorimetric assay available in a commercially available kit (Malate Assay kit; MAK067, Sigma Aldrich). Muscle mitochondria will be isolated according to the methods described by Iqbal et al. (2005). Myofibrillar and sarcoplasmic muscle fractions will be isolated using the protocol of (Carlson et al., 2017b). Mitochondrial efficiency (H2O2 production) will be assessed by quantifying carbonylation of mitochondri