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

The distribution of polychlorinated biphenyls (PCBs) in the milk fat globul e has been studied by sequential extraction of four different lipidic fract ions from powdered full-fat milk with supercritical carbon dioxide. Extract ions were carried out in the dynamic mode in the pressure range 13.6-23.3 M Pa at a temperature of 50 degrees C. The levels of PCBs and short-chain tri glycerides (SCT), medium-chain triglycerides (MCT) and long-chain triglycer ides (LCT), as well as the cholesterol in these four supercritical fluid ex traction (SFE) fractions were determined. Extracts obtained at lower pressu res 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 (r(2) in the range 0.9-0.999), and between the PCB and cholester ol levels (r(2) in the range 0.8-0.999, except for PCB 105) determined in t he SFE fractions. These results suggested a similar distribution of the PCB s and the cholesterol in the milk fat globule. This conclusion was also sup ported by the comparison of the PCBs and the cholesterol chemical structure s as well as by the total PCB levels determined by SFE to those obtained by using different extraction methods. The classical requirement for the anal ysis of this kind of lipophilic pollutants of an exhaustive extraction of t he lipids of the matrix to ensure their quantitative recovery has been revi sed. (C) 2000 Elsevier Science Ltd. All rights reserved.