In this study, the composition and content of vitamin D and its esters in 108 human milk samples from different lactation stages (colostrum on days 0–7, transition milk on days 8–15 , and mature milk after day 16) were analyzed by ultra-high performance liquid chromatography/quadrupole time of flight mass spectrometry (UPLC/Q-TOF-MS). The results showed that human milk contained 4 kinds of vitamin D and 20 kinds of vitamin D esters, 16, 18 and 14 kinds of vitamin D esters being found in colostrum, transition milk and mature milk, respectively. During the whole lactation period, the average contents of vitamin D₂ and 25(OH)-D₃ in colostrum were highest, 26.83 and 160.67 ng/L, respectively; the average content of vitamin D₃ in transition milk was highest, 119.87 ng/L; and the average content of 1,25(OH)₂-D₃ in mature milk was highest, 1.82 ng/L. The average contents of vitamin D esters in colostrum, transition milk and mature milk were 11.89, 10.73 and 11.47 ng/L, respectively, and the content of vitamin D₂ tetradecenoate (C_14:1) was highest throughout the lactation period. Through partial least squares-discriminant analysis (PLS-DA), colostrum, transition milk and mature milk could be well separated, indicating that the types and contents of vitamin D and vitamin D esters in human milk change from colostrum to mature milk. There was a correlation between different vitamin D esters. This study could provide data support for the development of infant formula.

The objective of this study was to investigate the effect of chlorophyll a versus b on the intestinal flora of mice induced by a high-fat diet (HFD) metabolomics combined with microbial diversity analysis. Results demonstrated that chlorophyll was transformed and degraded by the intestinal flora after 48 h culture in vitro. Its major derivatives included oxides (13²-hydroxy chlorophyll a, 15¹-hydroxy-lactone chlorophyll b, and 13²-hydroxy chlorophyll b) and magnesiumfree derivatives (pheophytin a and 13²-hydroxy pheophytin b). The reduced chlorophyll was degraded into non-fluorescent metabolites (m/z 666.2895), fluorescent metabolites (m/z 614.2735, 618.2684, and 792.3212) and pyrrole derivatives of propionate (m/z 223.0713). Microbial diversity analysis showed that the addition of chlorophyll down-regulated Escherichia-Shigella and up-regulated Acinetobacter, and chlorophyll a and chlorophyll b had different effects on the microbial abundance and species. Targeted metabolomics showed no significant difference in fatty acid contents among the control and chlorophyll addition groups. Untargeted metabolomics showed that chlorophyll addition resulted in differences in fecal metabolites (both chlorophyll a and b led to the synthesis of more antibiotics). These metabolites were mainly enriched in the caprolactam degradation pathway and the macrolide biosynthesis pathway 12, 14 and 16 for the chlorophyll a and b groups, respectively, with 15 shared pathways being found between the two groups. The results of this study will help to understand the effect of chlorophyll supplementation on the gut microbiota of HFD-induced mice, and provide useful information for understanding the interaction between chlorophyll and the intestinal flora.