Abstract: Breast milk is considered as the best food for infants and young children, and humanization is the basic principle for formulating infant formula. However, the composition of breast milk is extremely complex, so it is important to fully understand it. Amino acids are important nutrients in breast milk, and their contents are affected by many factors, including lactation stage (colostrum, transitional milk, early mature milk, and late mature milk), region (south and north) and parity. The purpose of this study was to evaluate the effects of different factors on the amino acid composition of Chinese human milk, and propose amino acid patterns of Chinese human milk in different lactation stages and amino acid patterns of early and late mature milk from different regions and seasons. A total of 1 640 breast milk samples were collected from eight cities in China to analyze the changes of amino acid contents in different lactation periods with five factors including region, parity, delivery season, birth situation and delivery mode. The Euclidean distance was used to calculate the similarity in amino acid composition among lactation periods and find the amino acid patterns with the minimum distance and the maximum distance. The breast milk samples were screened by the European distance to determine the recommended amino acid pattern for breast milk in different lactation periods. The results showed that region and delivery season had significant effects on the amino acid patterns of early and late mature milk. Multi-factor analysis would be needed to analyze the effects of delivery frequency, birth condition and delivery mode. The validity of the amino acid pattern of Chinese breast milk was verified by the coefficient of variation method, and the differences in the amino acid pattern in breast milk from different regions and seasons were proposed. The results of this study provide a reference for future research on the humanization of infant formula and nutritional research of breast milk and offer new ideas for the improvement and optimization of infant formula.

Key words: breast milk; amino acid pattern; lactation period; similarity analysis; protein