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Biotin in Human Milk: Methods, Location, and Chemical Form^1,2,

Department of Pediatrics, Divisions of Gastroenterology and Nutrition, University of Iowa College of Medicine, Iowa City, IA 52242

For infants, no Recommended Dietary Allowance for biotin has been published; the estimated safe and adequate intake seems to be based on measurements of human milk. However, published estimates of the biotin content disagree substantially. We sought to address several of the potential sources of disagreement by defining the conditions for the collection, storage, and subcompartment distribution of biotin in human milk using the [¹²⁵I]avidin assay. Composition of the collection vessel (glass vs. common plastics) had no effect on biotin content of human milk. The biotin content of milk did not change during storage at room temperature for at least 1 wk, at 5°C for at least 1 mo, or at -20°C or -70°C for at least 1.5 y. Biotin in the cell pellet and fat fraction accounted for <5% of that in the skim fraction. Of the biotin in the skim fraction, none (<3%) was reversibly bound to macromolecules, and <5% was covalently bound to macromolecules. We conclude that assay of free biotin will detect almost all of the biotin present in a sample of mature human milk.

KEY WORDS: • biotin • human milk • protein hydrolysis • humans

¹ Supported by the Program in Human Nutrient Requirements of the U.S. Department of Agriculture (87-CRCR-1-2331), the National Institute of Diabetes and Digestive and Kidney Diseases (R01 DK36823), and by Research Career Development Award DK01810 for D.M.M.

² Previously presented in part in abstract form [Langbehn, S. E. & Mock D. M. (1988) Biotin concentration in human milk subcompartments. Clin. Res. 36: 894A (abs.); and Mock, D. M., Langbehn, S. & Mock, N. I. (1989) Distribution of biotin within human milk fractions. Meeting N. Am. Soc. Pediatr. Gastroenterol. Nutr., Chicago, IL] and presented at the fifth annual international conference of the International Society for Research on Human Milk and Lactation, November 11–15, 1990, Asilomar Conference Center, Asilomar, CA.

³ To whom correspondence and reprint requests should be addressed.

Manuscript received 7 March 1991. Revision accepted 23 August 1991.