Determination of selenium concentration and its chemical forms in the milk of Kuwaiti and non-Kuwaiti lactating mothers

Abstract

The objectives of the present study were to compare the selenium status in the milk and plasma of Kuwaiti mothers with that of non‐Kuwaiti mothers during 0–18 months of lactation and to identify and compare the chemical forms of selenium in human milk and cow milk. Thirty‐four donors between 25 to 40 years of age (Kuwaitis, n = 17; non‐Kuwaitis, n = 17) were studied. Milk samples were obtained prior to the first feeding of the infant and blood samples were collected shortly after. Milk fractionation was performed by ultracentrifugation, gel‐column chromatography, and thin‐layer chromatography. Concentrations of selenium were analyzed using atomic absorption spectrophotometry and glutathione‐peroxidase by spectrophotometry. Concentrations of selenium in milk and plasma and content of proteins in milk were significantly higher in the Kuwaiti group than those of the non‐Kuwaitis during the first 12 months of lactation. The selenium profile in milk was parallel with those of total proteins, casein, and whey. In general, these parameters including the activity of glutathione‐peroxidase, were decreased as lactation was prolonged. The major chemical form of selenium in human milk was found to be selenomethionine. Cow milk did not appear to contain this compound, but might have a free selenium form that is neither selenite nor selenate. In conclusion, 1) the higher level of selenium in the milk of Kuwaiti mothers may reflect the high protein content of regional diets and traditional treatment with herbal medicines during post‐parturition and 2) selenomethionine is the major selenium‐containing compound located in the whey protein fraction of human milk, and this may enhance the bio‐availability of selenium. J. Trace Elem. Exp. Med. 14:57–67, 2001. © 2001 Wiley‐Liss, Inc.

Trace elements and their distribution in protein fractions of camel milk in comparison to other commonly consumed milks

“…Milk fractionation and gel-column chromatography. Milk fractionation was performed as described previously (Al-Awadi & Srikumar, 2001). Briefly, fat content of milk samples from humans, cows and camels were first separated by centrifugation at 4000 g for 30 min using a refrigerated Beckman centrifuge.…”

“…Determination of casein, whey and low molecular weight proteins. Milk protein concentrations were estimated as described previously (Al-Awadi & Srikumar, 2001). Commercially available pure casein and whey protein standards were suspended in the above Tris-HCl buffer and used to construct standard curves by measuring the absorbance at 280 nm.…”

“…Determination of trace elements in whole milk and in different milk fractions. Concentrations of zinc, copper, manganese, selenium and iron in whole milk samples, and in fat, casein, whey and low molecular weight fractions were analysed by atomic absorption spectrophotometer (Srikumar, 1993 ;Al-Awadi & Srikumar, 2001). Whole milk samples and milk fractions were first digested using a mixture of nitric and perchloric acid (4 : 1).…”

“…The human milk samples analysed in the present study were obtained from a parallel investigation where trace element status in the milk of Kuwaiti mothers was compared with that of non-Kuwaitis (n l 17, each ; Al-Awadi & Srikumar, 2001). Nationalities of the latter group were American, Egyptian, Indian, Czech and Taiwanese, representing the major groups of expatriates living in Kuwait.…”

“…For example, the absorption of several elements from human milk has been shown to be better than from cows ' milk (Franson & Lo$ nerdal 1983). In a previous study, we reported that selenomethionine is a major selenium-containing protein located in the whey fraction of human milk, but cows ' milk did not appear to contain this compound (Al-Awadi & Srikumar, 2001). It is probable that this may be the reason for a higher absorption of selenium from human milk than from cows ' milk.…”