. 2014 Feb 21;3:104. doi: 10.1186/2193-1801-3-104

Table 1.

Free amino acid content (μmol/dL) ¹ of human milk collected during three stages of lactation

	Stage of lactation:
	Colostrum	Transition	Mature	Statistical analyses: effect of maternal age (p value)
Essential FAAs ² :
Histidine	1.45 ± 0.15^a,3	2.31 ± 0.16^b	2.00 ± 0.16^b	p = 0.85
Isoleucine	0.54 ± 0.06^a	0.62 ± 0.07^a,b	0.71 ± 0.07^b	p = 0.89
Leucine	1.31 ± 0.19^a	1.69 ± 0.20^a	2.86 ± 0.20^b	p = 0.21
Lysine	2.72 ± 0.27^a	1.40 ± 0.29^b	1.28 ± 0.29^b	p = 0.54
Methionine	0.27 ± 0.03^a	0.35 ± 0.04^a	0.48 ± 0.04^b	p = 0.17
Phenylalanine	0.51 ± 0.08^a	0.89 ± 0.08^b	1.04 ± 0.08^b	p = 0.69
Threonine	4.77 ± 0.49^a	6.11 ± 0.53^b	7.33 ± 0.53^b	p = 0.08
Tryptophan	nd⁴	nd	nd	---
Valine	2.36 ± 0.23^a	3.76 ± 0.25^b	4.57 ± 0.25^c	p = 0.44
Non-essential FAAs:
Alanine	12.54 ± 1.56^a	21.33 ± 1.69^b	27.27 ± 1.69^c	p = 0.46
Arginine	1.56 ± 0.18^a	1.05 ± 0.19^b	0.95 ± 0.19^b	p = 0.87
Aspartic acid	2.41 ± 0.48^a	3.78 ± 0.52^b	5.56 ± 0.52^c	p = 0.31
Asparagine	nd	nd	nd	---
Cysteine	0.65 ± 0.15^a	1.28 ± 0.16^b	2.24 ± 0.16^c	p = 0.58
Glutamic acid	44.44 ± 5.96^a	91.25 ± 6.45^b	120.33 ± 6.45^c	p = 0.19
Glutamine	10.70 ± 2.64^a	33.40 ± 2.86^b	61.15 ± 2.86^c	p = 0.48
Glycine	4.94 ± 0.73^a	9.74 ± 0.78^b	13.23 ± 0.78^c	p = 0.76
Proline	3.70 ± 0.35^a	2.68 ± 0.38^b	2.61 ± 0.38^b	p = 0.89
Serine	4.12 ± 0.61^a	8.43 ± 0.66^b	12.55 ± 0.66^c	p = 0.69
Taurine	51.24 ± 2.39^a	42.49 ± 2.58^b	35.72 ± 2.58^c	p = 1.00
Tyrosine	0.68 ± 0.09^a	0.95 ± 0.10^b	1.02 ± 0.10^b	p = 0.43
Totals
Essential	13.93 ± 1.09^a	17.14 ± 1.17^b	20.27 ± 1.17^c	p = 0.13
Non-essential	136.98 ± 11.35^a	216.31 ± 12.26^b	282.54 ± 12.26^c	p = 0.67
All FAAs	150.91 ± 12.00^a	233.44 ± 12.97^b	302.82 ± 12.97^c	p = 0.79

¹Data are expressed as Least Squared Means (LSM) ± SEM. Estimates created from Mixed effects model.

²Classification of FAA based on Dietary Reference Intakes¹³.

³Different letters are statistically different from each other.

⁴nd = not detectable; below the limit of detection.