Representative sampling of human milk and the extraction of fat for analysis of environmental lipophilic contaminants

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Abstract
Directions for the quantitative recovery of fat from a representative sample of human milk are given. The sample of fat is required for the quantitation of the amounts of contaminants the breastfed infant consumes. To obtain quantitative recovery of fat, the analyst must: (a) determine the amount of milk ingested by the breastfed infant preferably by test weighing the baby before and after nursing; (b) sample 10 to 100 ml of milk which contains the same percent fat as the total nursing; and (c) extract fat from the milk with a recommended procedure. Precautions must be taken to exclude contaminants from milk during this process. However, regardless of our caveats above, any estimate of the infant's fat intake is only an approximation. The fat that the infant actually consumes cannot be precisely determined because of the nature of the feeding process. Also, while test weighing of the infant is desirable, studies done without can yield useful data for evaluation of maternal exposure, eg.., comparisons over time or with different populations. The analyst will select the method of sampling which will provide the amount of milk needed. Since this is likely to be at least 100 ml for purposes of extracting fat for the analysis of environmental lipophilic contaminants, one or more entire milkings may be needed. The nature of milk and the difficulties encountered in obtaining representative samples of milk and fat are discussed. The rationale for extraction of lipid in relation to the dielectric constants of the solvent mixtures is presented. The recommended extractions are: AOAC Mojonnier, AOAC chemical residues, and Radin, and alkylated Sephadex methods. The Folch and dry column extractions recover the fat but employ dichloromethane. The alkylated Sephadex and solid phase extractions require less milk for the determination of the lipophilic contaminants. The contaminant fraction can be separated from most of the fat, with these latter procedures eliminating or reducing clean up steps. However the solid phase method has not been compared to the recommended extractions for total milk lipid. Quantitation of the extracted fat is done by weighing the solvent free and dry sample.

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