Electron Transfer and Oxygen Reduction Kinetics of a Beef Sarcoplasm Film on a Polyion-Coated Electrode

Enabling electrochemical methods to directly probe native biological samples, rather than isolated proteins or cofactors, provides holistic insights of fundamental significance at the tissue and cellular levels. This study presents the first report of direct electrochemical analysis of a complex meat extract, specifically a sarcoplasmic film from beef longissimus lumborum muscle adsorbed onto a polyion-modified graphite electrode. We characterize its heterogeneous electron transfer kinetics and oxygen reduction behavior using cyclic voltammetry and compare the results with those of isolated myoglobin systems. Building on our previous electrochemical profiling of meat discoloration via peak potential shifts and current changes, this study advances the analysis by quantifying electron transfer kinetics and the oxygen reduction behavior of a sarcoplasmic film on modified electrodes. In the present report, the sarcoplasmic extract was adsorbed onto polyethylenimine (PEI)-coated graphite electrodes and studied under argon to evaluate scan rate-dependent electron transfer kinetics and under varied oxygen concentrations to assess electrocatalytic behavior. At pH 5.6, above its isoelectric point (∼pH 5.0), the negatively charged sarcoplasmic film was electrostatically adsorbed onto the positively charged PEI layer. The film exhibited an electroactive surface coverage of 23.6 ± 3.3 pmol cm–2 and a quasi-reversible heterogeneous electron transfer rate constant of 27.1 ± 2.2 s–1. The Michaelis–Menten oxygen binding affinity constant (KM) was 722 ± 62 μM, closely matching that of isolated myoglobin. By studying redox-active proteins in their native matrix, this work advances the field of protein electrochemistry and informs the future development of simplified bioelectrochemical interfaces.