Composition of the mother’s milk I. Protein contents ... contents, amino acid...

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  • Acta Univ. Sapientiae, Alimentaria, 2, 2 (2009) 174195

    Composition of the mothers milk I.

    Protein contents, amino acid composition,

    biological value.

    A review

    J. Csapo1,2


    Sz. Salamon1


    1SapientiaHungarian University of Transylvania,Cskszereda Campus, RO-530104, Libertatii 1., Miercurea-Ciuc

    2University of Kaposvar,Faculty of Animal Science,

    Guba S. u. 40, H7400 Kaposvar, Hungary

    Abstract. The authors have analysed protein contents, protein frac-tions, free amino acid and total amino acid contents of the motherscolostrum and mothers milk in comparison with the newest publications.They have established that there was no united picture of the differenteffects on protein contents of the mothers milk. Protein contents of thecolostrum of well-nourished mothers were found 6.0%, whereas those ofunderfed ones 4.5%. Some argue that there is a significant positive re-lationship between protein contents of food and daily protein intake, aswell as protein contents of the mothers milk. Some researchers werefound the protein contents of the underfed mothers milk to be lower,while others found no difference in true protein contents of the milk ofunderfed and appropriately fed mothers (0.81.0%), and more could not

    Key words and phrases: mothers milk, protein content, amino acid composition, biolog-

    ical value, NPN-content


  • Composition of the mothers milk I. 175

    evidence a difference in mothers of different nationality. Completed themothers nutriment with protein, in a part of the experiments proteincontents of the mothers milk increased, whereas others have reportedreducing protein contents when completting with protein.Concerning the protein fractions, casein contents of the colostrum weremeasured to be 3.8 on average; while those of the mature milk 5.7 g/dm3;which values were for the -casein 2.6 and 4.4 g/dm3, and for the -casein 1.2 and 1.3 g/dm3. -lactalbumin contents were found to be 3.62and 3.26 g/dm3; lactoferrin contents 3.5 and 1.9; serumalbumin contents0.39 and 0.41; immunoglobulin A contents 2.0 and 1.0; immunoglobu-lin M 0.12 and 0.20; and immunoglobulin G 0.34 and 0.05 g/dm3 in thecolostrum and the mature milk, respectively.NPN contents of the mothers milk were measured to be significantlyhigher (25% in total protein %) than those of the cows milk (5%), withmain component being the urea and free amino acids. It has been estab-lished that the total free amino acid provide only 2% of the requirementsof a newborn baby, in nutritional respect it is an important fraction asit is easily utilizable for the synthesis of the nerve tissue and the neu-rotransmitters. Free amino acids are very important for the afterbirthdevelopment; especially taurine, serine, glutamic acid and glutamine,which give a considerable portion of the total free amino acids. Taurinewas found to be essential for the development of the newborn, as taurineproduction from cysteinesulfonic acid is rather restricted due the lim-ited activity of the cysteinesulfonic acid decarboxylase enzyme. Taurinetakes part in the conjugation of the bilious acids and has a significantsrole in the formation of the retinal receptors. Serine has an importantrole in the casein synthesis, as well as it is a precursor of neuroactivesubstances, and a component of the biosynthesis of phospholipids. Highconcentration of glutamic acid in the milk can be useful, as glutamicacid has a key position in the amino acid metabolism, and convertedinto alpha-ketoglutaric acid it can enter the tricarboxylic acid cycle. Byanalysis the amino acid composition of the mothers milk protein it wasestablished that around 20% of it is glutamic acid, whereas it containsin the smallest amount histidine, cysteine and methionine. Proportionof the essential amino acids is around 42%, which abundantly cover therequirements of the newborns. Some have established a relation betweenessential amino acid contents of the milk protein and the essential aminoacid contents of the food, while others deny the existance of such a rela-tion. Cysteine/methionine ratio of the mothers milk is higher than thatof cows milk, the amount of phenylalanine and tyrosine is lower, due tothe higher proportion of the whey proteins.

  • 176 J. Csapo, Sz. Salamon

    1 Non-protein nitrogen content

    According to Emmett and Rogers [9] non-protein nitrogen content (NPN) ofthe mothers milk represents around 25% of the total nitrogen, including urea,uric acid, creatinine, free amino acids, amino alcohols, peptides, hormones, nu-cleic acids and nucleotides. Their significance is not fully clarified, but some ofthem contribute to the development of the new-born. The non-protein nitro-gen content derives mostly from the blood of the mother and during the lac-tation shows no considerable change. Various beneficial effects are attributedto non-protein nitrogen, such as e.g. the epidermic growth factor.

    Carratu and et al. [4] examined nitrogen-containing components, NPN con-tent of mothers milk in milk samples collected from 195 healthy mothersfrom different parts of Italy. The mothers fed their newborn babies exclu-sively with mothers milk for one month. The milk samples were collected atthe age of one month of the babies, and previously the mothers were taughthow to carry out a correct sampling. The samples were taken during the sec-ond and third feeding by hand, the drawn approx. 10 cm3 sample was collectedinto sterile polypropylene pots and stored at 20 C until the analyses. Aver-age age of mothers taking part in this experiment was 31 years, their averageweight 1 month after the birth was 63 kg, average body mass of the babieswere 3360 g, who consumed on the average 673 cm3 milk per day after theirbirth. NPN content (non-protein content) was 341mg/dm3 (extreme values:158 and 635mg/dm3). NPN represented around 15% of the total nitrogen. Itwas established that the NPN content of the mothers milk varies between widelimits. The great individual difference can be explained by the fact that thisfraction is a heterogeneous mixture of nitrogen-containing substances. SeveralNPN components of the mothers milk are metabolism products which enterdirectly from the mothers plasma into the milk gland.

    According to Agostini et al. [1, 2] NPN content of the mothers milk in-cluding peptides, urea, uric acid, ammonia, creatinine, creatine, nucleic acids,carnithine, amino acids and other components, cannot be regarded as of samevalue as milk protein nitrogen. NPN content of the mothers milk is signifi-cantly higher than that of the cows milk where this is only 5% of the totalnitrogen, while for the mothers milk this ratio can reach even 30 mg/100 cm3.

    According to examinations of Raiha [18] the mothers milk contains NPN ina relatively high concentration, up to 25% of the total nitrogen. Main compo-nent of this fraction is urea with a concentration of up to 25 mg/100 cm3, aswell as creatine (3.7mg/100 cm3), creatinine (3.5 mg/100 cm3), glucose amine(4.7 mg/100 cm3) and the free amino acids.

  • Composition of the mothers milk I. 177

    According to Picciano [17] NPN content of the mothers milk representsapprox. 2025% of the total nitrogen and remains relatively constant duringlactation. It contains around 200 fractions, most important of them are the freeamino acids, carnithine, taurine, nucleic acids, nucleotides and polyamines. Itappears that some of them, e.g. taurine, purine and pyrimidine bases areessential for the newborn baby.

    1.1 Urea content

    According to Wu et al. [21] urea content of the Taiwanese mothers is around3035 mg/100 cm3. Harzer et al. [11] investigated the change of the urea con-tent of the mothers milk in the early phase of lactation. They took from 10mothers altogether 78 milk samples (20 cm3) in the first five weeks of lacta-tion on the days 1, 3, 5, 8, 15, 22, 29 and 36, and refrigerated them immedi-ately at 30 C. No significant differences were found between the colostrum(525g/100 cm3), transitional milk and ripe milk (510g/100 cm3) in the ureacontent.

    2 Protein content and protein fractions

    Wu et al. [21] determined raw protein content of Taiwanese mothers. 264 milksamples were taken from 240 healthy mothers in different phases of lactation,and the samples were arranged in groups as per geographical position. It wasexperienced that crude protein content of the colostrum decreased very quicklyfrom 2.51% to 1.25% in ripe milk.

    Emmett and Rogers [9] examined protein content of the mothers milk inthe colostrum, transitional milk and the ripe mothers milk, also taking intoconsideration the physical condition of the mother. It was established thatthe protein content of the colostrum (2.0%) is substantially higher than in thetransitional milk (1.5%) or in ripe milk (1.3%).

    Marna et al. [14] examined the composition of milk of mothers living LaPlata in Argentina and established that protein content of milk was not af-fected by the nutrition of the mother as protein content of the milk of normal,overweight and fat mothers was 9.7; 9.1 and 9.1 g/dm3. Agostini et al. [1, 2]examining the protein content of mothers milk collected milk samples from16 mothers on the day 4 of the lactation (colostrum), and then in its firstand third month. Protein content was determined by the Kjeldahl method.The protein content decreased during the lactation from 1.93mol/dm3 to1.07mol/dm3.

  • 178 J. Csapo, Sz. Salamon

    Khatir Sam et al. [12] examined protein content of milk of Sudanese moth-ers. The mothers used a hand-pump for the sampling with the use of whichthey could take around 100 cm3 milk per person. Nitrogen content was de-termined by neutron activation analysis and x-ray spectrometry, respectively.Dry matter content of the milk was measured to be 10.4%, pr