| Fat is an important component of human milk,providing about 50% of the energy for infants.Triacylglycerol is the most important component of human milk fat,accounting for98%.The previous results of our group showed that human milk triacylglycerols have a specific structure,that is,the distribution of fatty acids in the carbon skeleton of triacylglycerols.Palmitic acid(16:0)in human milk is mainly in the form of 1,3-diunsaturated fatty acid-2-palmitate(UPU),and human milk is rich in a large amount of medium-and long-chain triacylglycerol(MLCT).The effects of these two types of triacylglycerol on fat digestion in infants are rarely reported.Based on this,this paper firstly analyzed the composition characteristics and influencing factors of MLCT and UPU-type triacylglycerols in human milk.And then we investigated the digestion characteristics of these two types of structured triacylglycerol by in-vitro digestion model simulating the infant gastrointestinal tract.The relationship between composition and structure of triacylglycerol and digestion products was also analyzed.The main research contents are as follows:Firstly,the composition characteristics of triacylglycerol in 204 human milk samples from6 cities were analyzed.The results showed that a total of 122 kinds of triacylglycerol were identified in human milk fat,of which 60 were MLCT-type triacylglycerols.And one mediumchain fatty acid(MLL)triacylglycerol accounted for 80% of the total MLCT.UPU-type triacylglycerols account for 38.93%,of which O-P-L and O-P-O were the predominant UPU,accounting for 16.04% and 13.90%,respectively.The ratio of OPL/OPO were greater than 1 in all human milk.The total content of MLCT and UPU in human milk is about 65%.The composition of MLCT and UPU in human milk varies greatly between different lactation periods and regions,but their total content is hardly affected by lactation periods and regions.Secondly,the relationship between maternal dietary structure and human milk triacylglycerol composition was analyzed.The results showed that MLCT in human milk was positively correlated with carbohydrate energy supply ratio(P<0.05),SSU-type triacylglycerol was positively correlated with fat energy supply ratio(P<0.05).However,the total content of MLCT and UPU in human milk was not affected by the ratio of nutrients.Comparing the differences of triacylglycerol content in human milk of different groups,it was found that the content of MLCT in human milk of carbohydrate group(27.52%)was significantly higher than that of the other two groups(P<0.05),and the content of UPU in human milk of protein group(40.20%)was significantly higher in the other two groups(P<0.05).However,there was no significant difference in the total content of MLCT and UPU in human milk of different groups.Finally,using a dynamic in-vitro digestion model simulating infant gastrointestinal and lipidomic technology,the digestion differences of 7 kinds of infant formula(IF)with different triacylglycerols composition were compared.And the relationship between triacylglycerol structure and digestion products was explored.The results showed that IF1,IF2,IF3 and IF5 contained a large amount of medium-chain fatty acids,which existed in the form of MLCT in IF1 and IF2,and in the form of medium-chain triacylglycerol in IF3 and IF5.The sn-2 position in IF1～IF5 is dominated by saturated fatty acids,while in IF6 and IF7 is dominated by monounsaturated fatty acids,mainly 18:1 n-9c.After in-vitro gastric digestion,the triacylglycerol content of IFs decreased only slightly,and the lipolysis degree of IFs with more medium-chain fatty acid content was higher at the end of gastric digestion,about 10%.After in-vitro intestinal digestion,the triacylglycerol content of the IFs decreased significantly,and the IFs supplemented with human milk structured fat(MLCT and sn-2 palmitate)had the highest lipolysis degree and released the most amount of free fatty acids.A total of 137 lipid molecules were identified from the digests using liquid chromatography-mass spectrometry.IFs supplemented with MLCT or coconut oil released more medium-chain fatty acids than other IFs.The medium-chain fatty acids released in the gastric phase by IFs supplemented with coconut oil accounted for a higher proportion of the total amount,about 30%.In addition,IFs supplemented with sn-2 palmitate released more monoglyceride-16:0 and O-P,while IFs without sn-2 palmitate released more O-O.In conclusion,this thesis clarified the composition characteristics of human milk MLCT and UPU and their relationship with the nutrient supply ratio.In-vitro digestion showed that the IFs containing human milk MLCT and sn-2 palmitate had better digestive properties.This study provides the basis and support for the development of IF oil and the evaluation of nutritional properties. |
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