Spatial and temporal mass spectrometric profiling and imaging of lipid degradation in bovine M. longissimus dorsi lumborum

Lipid oxidation plays a critical role in the quality of meat and meat products; however, lipid degradation is generally evaluated at a holistic level, without attention to spatial distribution. Marker lipids were selected based on their relative abundance and characteristic MS fragmentation patterns (10 phospholipids, 2 triglycerides, and cholesterol). These markers were subsequently utilised for temporal and spatial profiling of lipid degradation in bovine M. longissimus dorsi lumborum steaks subjected to high (packaged in 80% O2/20% CO2 modified atmosphere), atmospheric (oxygen permeable film) and ultra-low (vacuum-packaged) oxygen packaging during storage through matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight (MALDI–TOF/TOF) mass spectrometric imaging. Interestingly, markers showed highly contrasting effects in terms of their oxidative stability over time. The relative abundance of phophatidylcholines generally declined rapidly under high oxygen conditions. In contrast, PC 18:1/18:0 showed high relatively stability to oxidation. Cholesterol also displayed high relative stability. Overall, high oxygen packing was found to result in rapid lipid degradation, while vacuum-packaging significantly mitigated lipid degradation. Oxidative degradation profiles were spatially heterogeneous across meat sub-samples and differences were also observed from the centre and edge of the steaks. This new approach to tracking lipid degradation directly from meat samples offers increasingly precise tracking of modification in meat and other foods.