Elucidation of the lipid degradation process in soft tissue and fluid during decomposition, in the presence and absence of insects.
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Decomposition has been extensively studied in the presence of insects, however the process in the absence of insects has been considerably less documented. In this study, the decomposition process was compared between domestic pig carcasses in the presence and the partial and complete absence of insects during three consecutive summers. Fluid was collected from carcasses, from which pH and conductivity were measured. The fluid was analyzed via attenuated total reflectance- infrared spectroscopy (ATR-IR) and gas chromatography-mass spectrometry (GC-MS) to examine the fatty acid degradation trends, in an attempt to identify potential biomarkers for estimating the post mortem interval (PMI). Tissue was also collected, from which pH was measured and fatty acids extracted and analyzed by GC-MS. All results were compared between the carcass groups to investigate the effect of insects on the decomposition process. Observations of the physical changes exhibited by the exclusion groups required new decomposition stages to be established to better characterize the processes. The fluid analyses indicated that insects influenced the trends observed from the pH and conductivity measurements. The effect of insects on the bands detected by spectroscopic analysis was unclear, however GC-MS results demonstrated that insects accelerated the rate of hydrogenation when they were present in large numbers; evidence of hydrogenation was absent in both exclusion groups. Tissue pH was also influenced by insect activity and significant differences were observed between carcass groups in the amount of individual fatty acids detected during the insect activity stages and following the advanced decay and dry stages. Characteristic fatty acids were not identified that would allow them to be used to estimate PMI. Further research investigating the complete lipid degradation process is required to establish fatty acids of interest which would aid in establishing accurate and objective methods of estimating PMI, to be used in criminal cases.