Adipose tissue estimates the postmortem interval based on ATR-FTIR spectroscopy

Abstract

The estimation of the postmortem interval (PMI) is an essential part of forensic practice investigations. In this experiment, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and chemometrics were combined to explore the estimation of PMI in adipose tissue and the effect of temperature. Through principal component analysis (PCA) and two-factor ANOVA, we found that the change in adipose tissue degradation was mainly reflected in the peak intensity in the 1743 cm−1 (the bond between fatty acids and glycerol) decrease with the prolongation of PMI and the peak intensity in the 1711 cm−1 (free fatty acids) increase with the prolongation of PMI. Furthermore, temperature has a significant effect on the postmortem changes in adipose tissue; it will not change the mechanism of adipose tissue degradation but will affect the rate of adipose tissue degradation. Our next step was to establish partial least squares (PLS) regression models at different temperatures to estimate PMI. We found that the temperature affects the robustness and reliability of the model by affecting the rate of adipose tissue decomposition. In the high-temperature group, the adipose tissue changes more with time, which is beneficial to the detection of FTIR and the establishment of the model (25 °C: Rp2 = 0.82, RMSEP = 1.78 d; 35 °C: Rp2 = 0.82, RMSEP = 0.59 d), while low temperature is the opposite (5 °C: Rp2 = 0.12, RMSEP = 3.73 d; 15 °C: Rp2 = 0.60, RMSEP = 2.57 d). This study shows that the combination of ATR-FTIR and chemometrics is feasible to explore the estimation of PMI in adipose tissue and the effect of temperature.