我国南北城市0～12月不同泌乳阶段母乳蛋白质和氨基酸构成的纵向研究

Longitudinal Study of Protein Content and Amino Acid Composition of Breast Milk at Different Lactation Stages from Southern and Northern Urban Chinese Mothers

目的:比较我国北京(北方)和深圳(南方)两城市0～12月不同泌乳阶段母乳蛋白质和氨基酸含量差异。方法:于北京市和深圳市各招募30名足月分娩健康婴儿的健康乳母,纵向采集10次母乳,包括初乳(3～5 d)、过渡乳(13～15 d)和成熟乳(3、4周和2、3、4、6、9、12月),检测蛋白质和氨基酸含量并作比较分析。结果:北京和深圳母乳中蛋白质含量均为初乳中最高,随泌乳时间的延长而逐渐降低:其中,前3周急速降低,之后降低速度减缓,但仍有显著差异(P<0.05),到3月时达到稳定;两城市母乳在各泌乳阶段中均无显著差异(P>0.05)。母乳氨基酸含量也随着泌乳时间的延长呈显著下降趋势(P<0.05),到12月时总氨基酸含量、总必需氨基酸含量和总非必需氨基酸含量均下降了约58%。母乳中含量最丰富的单体氨基酸为谷氨酸、亮氨酸和天冬氨酸,含量最低的是蛋氨酸和色氨酸,两城市母乳单体氨基酸的绝对含量在除初乳和4月成熟乳以外的其他各月均有种类和数量的差异,但随泌乳时间的延长,各单体氨基酸在总氨基酸中的比例保持稳定,必需氨基酸和非必需氨基酸分别占总氨基酸的42%和58%左右;而深圳母乳中苯丙氨酸在总氨基酸中的比例在除3～5 d以外的其他9个时间点均高于北京母乳。结论:初乳中蛋白质和氨基酸含量均最高,随着泌乳时间的延长均呈逐渐下降趋势;蛋白质含量不受地区差异的影响,而两城市母乳中氨基酸含量及其在总氨基酸中的比例具有一定程度的差异。

Aim:To comparatively study the protein content and amino acid composition of breast milk at different lactation stages(0–12 months)from northern(Beijing)and southern(Shenzhen)urban Chinese mothers.Methods:Totally 30 lactating mothers of full-term infants were enrolled in Beijing and Shenzhen separately,and breast milk samples were collected between day 3 and 5(colostrum),between day 13 and 15(transitional milk),and at 3 and 4 weeks and 2,3,4,6,9 and 12 months(mature milk)following delivery for the determination of proteins and amino acids.Results:The highest protein content was detected in colostrum among the various milk samples from mothers in both cities and it gradually decreased with increasing lactation length,during the first 3 weeks rapidly and then more slowly but a significant difference being still observed(P<0.05),reaching a stable level at 3 months with no significant difference being found between the two cities for each lactation stage(P>0.05).Similarly,amino acid contents significantly decreased with increasing lactation length(P<0.05);the contents of total amino acids,essential amino acids and non-essential amino acids decreased by approximately 58%.Glutamic acid,leucine and asparaginic acid were the most abundant amino acids in breast milk,whereas methionine and tryptophan were the least abundant.Amino acid composition in breast milk differed between the cities for all lactation stages except colostrum and mature milk at 4 months.The proportion of each amino acid to the total amount remained stable with the prolongation of lactation,and essential and nonessential amino acids accounted for about 42%and 58%of the total amino acids,respectively.However,for all lactation times except colostrum,the proportion of phenylalanine to total amino acids in Beijing breast milk was higher than in Shenzhen breast milk.Conclusion:Human colostrum has the highest contents of proteins and amino acids among all lactation times,which decline with increasing lactation time.The contents of amino acids and the proportions to total amino acids but not the protein content of breast milk vary between cities.