| Human milk has been recognized as the best food for infants.And lipid provides energy required by infants and plays various biological functions.However,the dynamic change of lipid composition during lactation may affect its digestion and utilization in infants.At present,analysis of lipid composition in the whole lactation stage is not thorough yet.And there is limited comparative research on the differences of digestive characteristic of milk fat in different lactation stages.Therefore,this paper took human milk in five different lactation stages(colostrum,transitional milk,mature milk early(1),middle(2)and late(3))as research object,and deeply explored the influence of lactation period on lipid composition.In addition,differences on digestive characteristic of human milk fat in different lactation periods and their correlation with lipid composition were analyzed.Results here provide theoretical reference for lipid designing and segmentation of infant formula and help to realize the precise breastfeeding.The main research contents are as follows:Firstly,lipid content and composition of human milk from different lactation stages were determined.The results showed that the level of human milk lipid increased with lactation period(2.3±1.06%～4.54±1.06%).Colostrum had the highest level of monounsaturated fatty acid(MUFA,37.87±5.15%)and long-chain fatty acid(LCFA,96.31±2.89%).Saturated fatty acid(SFA)was the most prevalent fatty acid situated at sn-2 and enriched in mature milk1(79.14±13.60%).A total of 16 subclasses of 468 lipids were identified.Colostrum had the most abundant lipid species and was enriched in high acyl carbon number(ACN,46～54)of triacylglycerol(TG)with LCFA and unsaturated fatty acid(UFA).TG with ACN between 36 and 44 was enriched in transitional milk.In addition,transitional milk showed the most abundant of medium chain triacylglycerol(MCT,1.36±0.89%)and medium-and long chain triacylglycerol(MLCT,49.64±5.10%).The content of phosphatidylcholine(PC)>phosphatidylethanolamine(PE)> sphingomyelin(SM).Mature milk1 was rich in PE(7.93±2.75%),while phosphatidylinositol(PI,9.87±3.27%)and ceramide(Cer,48.03±5.55%)showed the most level in mature milk2 and SM(17.39±3.43%)was prevalent in mature milk3.Secondly,human milk simulated digestive system was constructed based on human milk at different lactation stages.The results showed that free fatty acid(FFA)release rates in gastric phase were colostrum(20.50±2.31%)> transitional milk(14.21±0.39%)> mature milk(<5%).The FFA release rates of mature milk1 and mature milk3 in intestinal phase were the most.The total FFA release rates were mature milk1(80.27±7.48%)≈ colostrum(79.48±1.40%)>mature milk3(68.02±3.70%)> transitional milk(61.24±2.24%)> mature milk2(44.02±0.67%).The degree of hydrolysis of MLCT in colostrum was the smallest,and the amount of monoacylglycerol(MG)produced was the least(9.21±1.45%),mainly MG 16:0.The proportion of diacylglycerol(DG)in transitional milk was the largest(68.47%)and mainly DG(16:0/18:0).The content of C18:2n-6 released by mature milk1 was the highest(27.19±1.84%).The contents of C12:0(3.76±1.01%)and C14:0(2.52±0.89%)were the lowest,while C18:1n-9 was the highest(47.59±4.38%)in mature milk2.The degree of hydrolysis of MLCT and the content of C10:0(1.28±0.35%)released were the highest in mature milk3.Finally,lipid simulated digestive system was constructed based on human milk at different lactation stages.The results presented that FFA release rates in gastric phase were colostrum(8.33±1.12%)> transitional milk(6.47±0.04%)> mature milk(<5%).FFA release rates of intestinal(24.91±1.23%～80.02±1.36%)and the final(33.24±2.36%～80.09±1.36%)increased with lactation period.The release of C12:0 in colostrum was the highest(5.38±1.24%).The release of SFA in transitional milk was the highest(56.21%)and mainly C16:0.The release of C10:0 in mature milk1 was the highest(1.02±0.12%).The release of C14:0 in mature milk2 was the lowest(2.79±1.11%),and C12:0 in mature milk3 was the lowest(2.69%).The lipid composition of digestive products depends on the composition and distribution of fatty acid in samples before digestion.The contents of MG and DG are mainly affected by the composition of sn-2 fatty acid,while the contents of FFA are affected by the composition of both fatty acid and sn-2 fatty acid.In conclusion,this thesis revealed differences of lipid composition and digestive characteristic of human milk at different lactation stages.The influence of lipid composition on digestive characteristics was also clarified.Results showed that the composition of lipid digestive products was significantly correlated with the composition and distribution of fatty acids in samples before digestion This study provides theoretical basis for lipid designing and rational segmentation of infant formula. |
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