Study of the distribution of the polychlorinated biphenyls in the milk fat globule by supercritical fluid extraction

The distribution of polychlorinated biphenyls (PCBs) in the milk fat globule has been studied by sequential extraction of four different lipidic fractions from powdered full-fat milk with supercritical carbon dioxide. Extractions were carried out in the dynamic mode in the pressure range 13.6-23.3 MPa at a temperature of 50 degrees C. The levels of PCBs and short-chain triglycerides (SCT), medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), as well as the cholesterol in these four supercritical fluid extraction (SFE) fractions were determined. Extracts obtained at lower pressures were found to be enriched in PCBs, SCT, MCT and cholesterol, while the concentrations of all these analytes decreased for subsequent extractions. Satisfactory quadratic correlations were found between the PCB and SCT and MCT levels (r2 in the range 0.9-0.999), and between the PCB and cholesterol levels (r2 in the range 0.8-0.999, except for PCB 105) determined in the SFE fractions. These results suggested a similar distribution of the PCBs and the cholesterol in the milk fat globule. This conclusion was also supported by the comparison of the PCBs and the cholesterol chemical structures as well as by the total PCB levels determined by SFE to those obtained by using different extraction methods. The classical requirement for the analysis of this kind of lipophilic pollutants of an exhaustive extraction of the lipids of the matrix to ensure their quantitative recovery has been revised.