3.4. Comparation of triacylglycerol composition in breast milk of different dietary groups
In order to intuitively show the difference of MLCT composition and UPU composition in different groups of breast milk, their compositions were made into a box line diagram, as shown in Fig.1. According to Fig.1, the carbohydrate group had the highest MLCT (~27%) and the lowest UPU (~38%) in breast milk. On the contrary, the content of UPU (~41%) in breast milk of the proteome group was higher than that of other groups, and the content of MLCT (~23%) was lower than that of other groups. This is consistent with the positive correlation of the protein energy ratio with the amount of UPU in the breast milk. The total content of MLCT and UPU in breast milk of the three groups was very close, maintained at ~65%, and there was no significant difference, indicating that the total content of MLCT and UPU in breast milk was not affected by dietary structure.
Principal component analysis (PCA) was performed on the MLCT components in breast milk of the three groups to further show the differences of MLCT components in breast milk under different dietary patterns. From Fig.2, it can be seen that although some breast milk samples from different dietary groups are clustered together, their distribution is significantly different, indicating that there are significant differences in the composition of MLCT in breast milk from different dietary patterns. For example, the breast milk samples of carbohydrate group were mainly distributed in the first, third and fourth quadrants, while the other two groups were distributed in four quadrants. The distribution of carbohydrate group was significantly different from that of the other two groups, indicating that the composition of MLCT in carbohydrate group was significantly different from that of the other two groups. The fat group was very close to the protein group, almost overlapping, both concentrated in the second and third quadrants, but the breast milk samples of fat group were more dispersed. The difference in the composition of MLCT in breast milk is related to the dietary structure of the mother, but further studies are needed to clarify.
The 21 kinds of TAGs with a content greater than 1 % in the three groups of breast milk were made into a cluster heat map to show the differences more intuitively in TAG content in breast milk of different dietary groups. The results are shown in Fig.3, and the differences in TAG composition in breast milk of different dietary groups were further analyzed. As can be seen in Fig.3, the carbohydrate group breast milk is rich in MLCT such as O-L-La, O-P-La, and O-L-M, the fat group breast milk is rich in SSU type, such as O-P-P, S-P-L and S-P-O, while the protein group breast milk is rich in SUU type especially UPU type, such as O-P-L and O-P-O. About 70 % of palmitic acid is distributed in thesn -2 position of TAG, and stearic acid, oleic acid, linoleic acid and linolenic acid are mainly distributed in the sn -1,3 position, which is conducive to the absorption and utilization of fat and minerals (Watkins et al., 2003). However, due to the current research on the relationship between dietary structure and breast milk TAG composition, it is not clear why there are differences in breast milk TAGs in different dietary groups. Future studies should focus on the effect of maternal diet on TAG composition in breast milk to better guide the diet of lactating women. This study confirmed that the energy supply ratio of carbohydrate in Chinese mothers was positively correlated with the content of MLCT in breast milk (P < 0.05), the energy supply ratio of protein was positively correlated with the content of UPU (P < 0.01), and the energy supply ratio of fat was positively correlated with the content of SSU (P < 0.05).