The Composition And Metabolic Characteristics Of Medium-And Long Chain Triacylglycerol In Human Milk Fat

The main componment of human milk fat is triacylglycerols which accout for about 98%.Its unique composition and structure is associated with related to the digestion,absorption and metabolism of milk fat in infants.Human milk fat is naturally rich in medium-and long chain triacylglycerols(MLCT).However,infant formulas contain few the similar MLCT composition.The composition differences between human milk and infant formuas may lead to the metabolic differences in infants,which have not been considered.Therefore,this study aimed to systematically analyze and compare the MLCT composition and in vitro digestive characterics between infant formulas and human milk.Then,the MLCT structured lipid containing similar composition with human milk fat was prepared and its metabolic characteristics were investigated in mice.The main results are as follows:Firstly,the composition and structure of MLCT in human milk fat and the influences of gestation and lactation were studied.The results showed that the main medium chain fatty acids are lauric acid(4.64%)and myristic acid(5.33%),followed by capric acid,the least caprylic acid less than 0.1%.These medium-chain fatty acids of human milk fat are in the form of MLCT,not the medium-chain triacylglycerols(MCT).The content of MLCT was about 30.38%of total triacylglycerols when the fatty acids C₈-C₁₄are defined as medium-chain fatty acids.The MLCT in human milk fat are one medium-chain fatty acid type(MLL)and unsaturated triacylglycerols,which mainly composed of one medium-chain fatty acid such as lauric acid or myristic acid,and two long-chain fatty acids such as palmitic acid,oleic acid or linoleic acid.Lactation had a significant influence on the composition of MLCT in human milk,while gestation had little effect.Secondly,the composition of MLCT in infant formulas with various sources of medium-chain fatty acids including cow'milk(CF),plant-oil(PF),cow's milk/plant oil(CPF),goat's milk/plant oil(GPF)and special medical use formulas supplemented with MCT(SMF),was analyzed and compared with human milk fat.The results showed that when medium-chain fatty acids were defined as C₈-C₁₄,the contents of MLCT and MLL in all infant formulas were remarkably lower than that in human milk.Different from the compositional feature of MLCT in human milk fat,PF are charactered with Ca La M,La La P,etc.CF are charactered with Bu MS,Bu La P,etc.CPF and GPF are charactered with Ca MP,Ca PO,etc.SMF are charactered with Cy Ca Ca and Ca Ca Ca.Furthermore,the in vitro digestive characteritics of infant formulas and human milk were studied.During in vitro gastric and intestinal digestion,infant formulas added with MCT showed higher lipolysis degree compared with the common infant formula,however,the lipolysis of infant formulas was still lower than that of human milk after 120 min in the intestinal phase,indicating that high levels of MCT could promote the lipolysis of infant formulas in the early time periods.The composition of free fatty acids released during each digestion phase was also analyzed.Higher amounts of medium-chain fatty acids were released from infant formulas than human milk.And the infant formula containg a certain amount of MLCT released lower medium-chain fatty acids than the infant formula containg similar content of medium-chain fatty acids but few MLCT,indicating that MLCT combining medium-chain fatty acids with long-chain fatty acids in the same triacylglycerol could modulate their digestion.Therefore,there were significant differences in the MLCT composition between infant formulas and human milk,which could lead to the different digestive behaviors.Next,based on the MLCT composition of human milk,structured lipids enriched with MLCT were synthesized from fish oil and coconut oil through enzymatic interesterification.And then,the molecular distillation was used to purify the interesterificated products.The physical properties of final structured lipids were also ananlyzed.Through the single factor experiments,the optional conditions were obtained,and the content of MLCT reached62.14%,and the content of MLL-type triacylglycerols was 39.85%.When the evaporation surface temperature was 200(?),the content of triacylglycerols in the structured lipids was98.35%,the content of MLCT increased to 72.60%.Moreover,the structured lipids had similar MLCT composition with human milk,a better oxidative stability,lower solid fat content,and the acid and peroxide value were at or over the corresponding national standards.Finally,the effects of different fat on the growth performance,energy metabolism,fat metabolism and intestinal development of mice fed on high-fat diet based on the fat ingredient used in infant formulas were evaluated.The results showed that the high-fat blank group had signicant higher weight gain,body fat,elevated blood lipid level and abnormal liver function,lower respiratory quotient and microbial richness and diversity than normal control group.Compared with the physical mixture group,the MLCT structured lipid group showed an increase of energy expenditure,a decrease of body gain and serum triglyceride level,significant lower aspartate aminotransferase level,epididymal fat and perirenal fat weight and adipocyte size,which were not dramatically different from the normal control group.Moreover,the abundances of some microbiomesrelated to obesity such as Firmicutes/Bacteroidota and Desulfovibrionaceae were significantly reduced,however,the abundances of Rikenellaceae and Muribaculaceae were significantly increased in the mice of structured lipid group.It suggested that the MLCT structured lipid could inhibit the accumulation of visceral fat,improve the liver functions and alter the intestinal microbiota of mice fed high-fat diet.To sum up,this thesis made a clear composition and structure of MLCT in human milk fat,and difference between the infant formulas and human milk,prepared the structured lipid enriched with MLCT similar with human milk,evaluated the metabolic characteristics and found that it could inhibit the visceral fat,improve the liver function and regulate lipid metabolism of mice.The results could provide theoretical basis for the development of highly breastfed infant formula food.