CHAPTER 32:Analysis of Human Milk Lactose

Lactose is found almost exclusively in milk and is especially high in human milk. Indeed, lactose is the principal solid component of human milk, consistent with the essential role of this disaccharide in infant development. Lactose is often measured in human milk clinically to calculate the availability of calories administered to premature infants, where there is a fine line between undernutrition and overnutrition. For basic research, knowing lactose content at various stages of lactation helps understand requirements for early development, designing human milk substitutes, and studying lactogenesis. Human milk also contains appreciable amounts of other glycans that confound lactose quantification, including oligosaccharides, monosaccharides, glycolipids, glycopeptides, glycoproteins, glycosaminoglycans, and mucins. The many techniques for measuring lactose differ in their abilities to distinguish human milk lactose from the other glycans, and have other strengths and limitations. This chapter reviews the most common methods for lactose analysis in human milk: gravimetric proximate analysis, classical chemistry to produce chromophores, enzymatic analysis, spectrophotometry in the infrared region, and chromatographic resolution with detection by refractive index, pulsed amperometric detection, or mass spectrometry. We also describe our highly specific analysis of human milk lactose by LC-MS that is precise, rapid, and facile.