Colostral and mature breast milk protein compositional determinants in Qingdao, Wuhan and Hohhot: maternal food culture, vaginal delivery and neonatal gender.

Background and Objectives: Breast milk proteins are essential to infants as they provide nutrition and protection. This study evaluated multiple factors that might influence breast milk proteins to identify the determinants that lead to inter-individual and longitudinal differences. Methods and Study Design: Five major breast milk proteins (beta-casein, alpha-lactalbumin, lactoferrin, serum albumin and kappa-casein) from breast milk samples collected from 55 mothers in three cities (Hohhot, Wuhan and Qingdao) in China were analyzed using a validated ultra-performance liquid chromatography-mass spectrometry method. Various factors were statistically evaluated for their associations with breast milk proteins: mother's age, parity, delivery mode, infant gender and infant birth-weight. Results: Although decreased in concentrations, the proportions of beta-casein and alpha-lactalbumin increased from colostrum (33.8% and 26.8%) to mature milk (40.3% and 31.6%), respectively. Mothers of older age were found to produce a lower concentration of total protein. Compared with vaginal delivery, caesarean section was associated with lower concentrations of kappa-casein, lactoferrin and beta-casein in mature milk. Infant gender influenced breast milk proteins in colostrum: mothers who delivered a girl tended to produce more kappa-casein, lactoferrin and total protein. Furthermore, regional differences were found, and mothers from Hohhot produced significantly higher concentrations of alpha-lactalbumin and lactoferrin than those from Qingdao and Wuhan. This regional difference might be linked to the different dietary patterns of these mothers among cities. Conclusions: Our study deepens the understanding of breast milk protein dynamics in Chinese population and provides evidence on potential determinants, which can serve as guidance for infant nutrition optimization.