The Composition Of Branched-chain Fatty Acid In Human Breast Milk,vernix Caseosa,meconium And Its Influence On The Intestinal Flora Of Newborns

Branched-chain Fatty Acid（BCFA）is a functional saturated fatty acid with one or more methyl branching points on the carbon chain,which can be divided into isomeric（iso-BCFA）anti-isomeric–BCFA（anteiso-BCFA）.Previous studies have indicated that BCFA plays an extraordinary role in changing bacterial membrane structure,regulating virulence,and the intestinal flora composition due to its particular branched-chain structure.Different kinds of BCFA exist in human secretions and mammal milk but with few contents,which to our knowledge has not previously been widely studied.This research systematically analyzed the composition of BCFA in the human breast milk,vernix caseosa,meconium samples at the different gestational ages and mammal milk.Meanwhile,it is was studies investigated the source and route of BCFA in newborns’intestines,as well as its effect on the intestinal flora.The following were the essential contents and findings of the study:Firstly,Gas chromatography combined with mass spectrometry（GC-MS）was used to identify the fatty acid composition in 32 human breast milk at different gestational ages and lactation periods,and 56 fatty acids were identified.The results showed six iso-BCFA,three anteiso-BCFA,and one non-terminal methyl BCFA（6-methyl hexadecanoic acid）in the human breast milk.There was a significant effect between the gestational ages,lactation periods,and the content of BCFA in the human breast milk（p<0.01）.However,gestational age had a more significant impact on BCFA than lactation periods.Whether it was colostrum or transitional milk,the content of BCFA of term infants was highly significantly higher than that in preterm infant human breast milk（p<0.001）.Through investigation and statistics of sample background information,it was found that there was only one correlation between the content of iso-BCFA in the human breast milk and the mode of delivery.Secondly,optimized thin-layer chromatography（TLC）technology combined with GC-MS analyzed lipid and fatty acid composition in 51 vernix caseosa and 51 meconium at different gestational ages.Eighty fatty acids and seventy-three fatty acids were identified in the vernix caseosa and meconium,respectively.The results showed that wax esters and cholesterol esters were the most critical lipid components in the vernix caseosa and meconium,respectively.In contrast,vernix caseosa contained abundant lipids than meconium,like some diol diesters and free fatty acid.The vernix caseosa of full-term infants contained 34 various kinds of BCFA.The length of the fatty acyl chain was distributed between C₉-C₂₈,accounting for about 38.19%,iso-16:0 was the main BCFA,followed by iso-14:0.Compared with early preterm infants,it can meet the infants’needs during the pregnancy.However,only 29 BCFA were identified in the meconium of full-term infants with lower content than the vernix caseosa（p<0.05）.The fatty acyl chain length was distributed between C₁₁-C₂₆,indicating that the infant’s gastrointestinal tract can digest and absorb part of BCFA.The content of BCFA in vernix caseosa and meconium of full-term infants was significantly higher than that in preterm infants（p<0.05）.According to the calculation,the daily intake of BCFA in full-term infants before birth and within one week after birth was about 13.63 mg and 101.37 mg,significantly higher than that in early preterm infants（8.96 mg and 54.56 mg,p<0.01）.Then,16S rRNA sequencing and GC-MS were analyzed on 14 meconium of infants to find the relationship between BCFA and the intestinal flora.The results showed significant differences in the composition of newborns’intestinal flora at different gestational ages and genders.The main dominant bacteria in male newborns were Lactobacillus,while in female newborns was Pseudomonas.It may be related to the intake of different BCFA from the vernix caseosa.The correlation analysis of the eight main bacteria at the phylum level in the newborns’intestinal tract and the four major types of BCFA showed that both Firmicutes and Bacteroidota were related to iso-BCFA and BCFA,but the correlation between them is opposite.There was a negative correlation between Actinobacteriota and anteiso-BCFA,while Cyanobacteriota and Spirochaetota had a positive and negative correlation with hydroxy fatty acid（OHFA）.Bacteroidota had the strongest correlation with BCFA among them（p<0.01）.This may be related to the abundant BCFA in its cell membrane.Finally,the composition and content of BCFA in four kinds of ordinary mammal milk（cow milk,goat milk,yak milk,and camel milk）and three kinds of milk processing by-products（anhydrous cream,whipping cream,buttermilk powder）were analyzed by GC-MS and compared with human breast milk.The results showed that except goat milk（0.39±0.02 g/L）,the content of BCFA in mammal milk ranged from 0.62 g/L to 3.70 g/L,which was significantly higher than human breast milk（p<0.05）,and the BCFA in cow milk was closer to that in the human breast milk.Besides,the content and types of BCFA in different milk processing by-products are slightly different.Anhydrous butter has the highest BCFA content.The BCFA in these three products was more abundant than human breast milk.They may be raw materials for potential enrichment of BCFA.