Case Study: Electrophoretic separation of bovine myosin heavy chain in samples stored long term at −20°C

ABSTRACT Objective Samples used for skeletal-muscle, fiber-type profiling are traditionally collected fresh and stored at −80°C until analysis. This study aimed to assess the vi-ability of using aged beef samples in prolonged storage at −20°C for muscle fiber typing. Materials and Methods A total of 40 beef semimem-branosus steaks vacuum packaged at 14 d postmortem and stored at −20°C for 17 to 20 mo were used to deter-mine the relative expression of type I and type II myosin heavy chain (MyHC) isoforms via SDS-PAGE. Sample preparation included homogenization, myofibrillar protein purification, and protein load standardization. For SDS-PAGE, the final separating gel had 8% acrylamide, 37% glycerol, and 50:1 acrylamide:bis-acrylamide (2% C). The gel was imaged to quantify relative protein abundance af-ter destaining. Results and Discussion Denaturing SDS-PAGE doc-umented clear MyHC isoform separations, with a relative expression of 39.8 ± 6.8% type IIx, 36.0 ± 5.0% type IIa, and 24.2 ± 7.4% type I. The results suggest that the MyHC isoform in aged beef skeletal muscle samples stored at −20°C for up to 20 mo was able to generate relatively clear bands during electrophoresis. Implications and Applications Muscle fiber typing can be a valuable tool for evaluating meat quality traits such as pH, color, and aging potential through the assess-ment of muscle fiber composition. The evaluation outlined in this study is relevant in conditions where liquid nitro-gen or the collection of fresh samples is not feasible. Fur-thermore, the results indicate that denaturing SDS-PAGE can be used for muscle fiber typing in aged samples kept under long-term −20°C freezing conditions. This proof-of-concept study shows potential opportunities in exploring muscle fiber typing in existing skeletal muscle samples al-ready in cold storage.