Speciation of Zinc in Low Molecular Weight Proteins of Breast Milk and Infant Formulas by Size Exclusion Chromatography/Flame Atomic Absorption Spectroscopy

Abstract

Size exclusion chromatography (SEC) and flame atomic absorption spectroscopy (FAAS) were used for the separation of metal-containing species in milk whey. After milk ultracentrifugation, the sample was injected into a TSK-Gel G2000 glass column and eluted with 0.2M NH4NO3–NH3, pH 6.7. Low molecular weight proteins were fractionated, and the fractions were characterized by molecular weight. Zinc distributions were obtained by FAAS using a high performance nebulizer. The method was very sensitive (limit of detection = 2.6 × 10−3 μg/mL; limit of quantitation = 8.9 × 10−3 μg/mL) and precise (RSDs ≤ 10%). This method was applied to the determination of Zn in binding compounds in breast milk whey and in commercial cow's milk-based formulas. Distribution patterns were different. The presence of Zn in most fractions in breast milk was most significant, whereas in infant formulas Zn was detected only in fractions of molecular weight <5 kDa and in the highest molecular weight peak.

Separation of Selenium, Zinc, and Copper Compounds in Bovine Whey Using Size Exclusion Chromatography Linked to Inductively Coupled Plasma Mass Spectrometry

“…Regarding the zinc in the 4 kDa peak, its identity is unclear. The high proportion of low-molecular weight zinc agrees with previous findings showing that >50% of the zinc occurred in fractions with <5 kDa in whey prepared from human milk or formula based on cow milk, although the variation between samples was considerable (43).…”

Multi-elemental fractionation in milk whey by size exclusion chromatography coupled on line to ICP-MS

“…The results detailed in this work are similar to those obtained by Bermejo et al 30 They found that zinc was present, in the case of formula milk whey, in two different fractions (w160 kDa and v5 kDa, respectively). However, in human milk whey, they found that zinc was distributed among different fractions, showing an important peak in the molecular weight region related to serum albumin and lactoferrin.…”

Multielemental distribution patterns in premature human milk whey and pre-term formula milk whey by size exclusion chromatography coupled to inductively coupled plasma mass spectrometry with octopole reaction cell

“…These speciation data in milk whey obtained here agree well with those reported by others in the literature. 17,18,20,21,28 In pre-term formulaes, Zn turned out to be distributed between a HMW (435 kDa) fraction and, mainly, in a LMW fraction (v10 kDa). Also, the levels of total Zn present in the five pre-term formulae analysed were higher than those observed in breast milk.…”