Preparation And In Vitro Digestion Of Human Milk Substitute Fat Containing OPL Structural Lipid

The lipid component in infant formula milk powder is called human milk substitute fat.Its purpose is to simulate the composition,structure and nutritional properties of human milk fat（HMF）.However,currently commercially available milk powder only simulates HMF well at the fatty acid level.There is still a big gap between 2-position fatty acids and triglycerides（TAG）and HMF,especially 1-oleic acid-2-palmitic acid-3-linoleic acid triglyceride（OPL）,which is rich in HMF in China.In this thesis,the synthesis pathways of two OPL structural esters were compared,and the optimal synthesis conditions were determined.Thus,human milk substitute fats rich in OPL structural esters were prepared,and their digestive characteristics were studied through the infant in vitro digestion model.The main research contents are as follows:First,a solvent fractionation method is used to enrich tripalmitate triglyceride（PPP,93.86%）from palm stearin,using high-purity oleic acid（OA）and linoleic acid（LA）as acyl donors,using two steps Method enzymatic acid hydrolysis to synthesize OPL structural ester.The first step:PPP reacts with OA to synthesize OPO structural ester,the best reaction conditions are determined through single factor experiment,and the scale-up experiment is carried out under this condition,and the crude OPO product obtained is refined by physical distillation.The obtained product contains PA and OA.The content is34.20%and 57.94%,respectively,and the OPO content is 72.54%.The second step:OPO product reacts with LA to synthesize OPL structural ester,and the best conditions are determined through single factor test,and the relative content of palmitic acid in sn-2position（%sn-2 PA）in the product is 62.35%,PA,OA The content of LA and LA are29.81%,38.94%and 27.18%,respectively.It is inferred that there are other triglycerides in the product besides OPL structural esters.Secondly,the free fatty acids obtained from the mixed hydrolysis of camellia seed oil and sunflower seed oil are used as acyl donors（the content of OA and LA are 43.33%and 44.12%）,and they are subjected to one-step acidolysis reaction with PPP to synthesize OPL structural esters.The single factor test is passed The best reaction conditions are as follows:the amount of enzyme added is 12%,the molar ratio of PPP/mixed fatty acid is 1:12,the reaction time is 4 h,and the reaction temperature is55℃.On this basis,the response surface optimization was carried out,and the content of%sn-2 PA,OA and LA was used as the response value to determine the optimal process conditions:reaction time 5.30 h,PPP/mixed fatty acid molar ratio 1:14,and enzyme amount 12.80%,The reaction temperature is 60.00℃,and the content of%sn-2 PA,OA and LA in the obtained product are 70.36%,29.29%and 26.11%,respectively.The scale-up experiment and crude product refining were carried out under optimal conditions.The final product contained 36.20%OPL and 17.90%OPO structural ester,which could be used as the raw material for the next step to prepare human milk substitute fat.Thirdly,combined with the characteristics of currently commercially available milk powder oils,17 kinds of natural animal and vegetable oils and OPL structural esters are used as base oils,based on the composition of Chinese HMF’s macro total fatty acids,sn-2 fatty acids and triglycerides,and a physical blending model is adopted.Three different sources of human milk substitute fat were prepared:Compound plant-based human milk substitute fat（HMFS-P）was coconut oil:olive oil:sunflower oil:linseed oil:corn oil:lard:OPL=18.26%:3.92%:0.79%:2.76%:1.40%:8.26%:64.31%,compound milk/plant-based human milk substitute fat（HMFS-C）is cow milk fat:linseed oil:coconut oil:soybean oil:lard:OPL=42.62%:1.85%:13.43%:10.96%:5.05%:26.08%and compound goat milk/plant-based human milk substitute fat（HMFS-G）are goat milk fat:linseed oil:coconut oil:soybean oil:lard:OPL=29.90%:2.35%:12.12%:4.07%:7.73%:46.56%.The similarity evaluation showed that the total similarity between HMFS-C and HMF was the highest（G=83.50）,and its G_FA,G_sn-2 FA,and G_TAG were80.25,91.03 and 79.23,respectively,which can be considered as a highly similar human milk substitute Fat;HMFS-G comes next（G=81.85）,and its G_FA,G_sn-2 FA,G_TAG are85.91,76.75 and 85.89 respectively,which can be considered as a good substitute for human milk fat;HMFS-P is the lowest（G=77.12）,But it is still higher than the current commercial milk powder（G<60）.Finally,with HMF as a reference,three kinds of human milk substitute fats were prepared as the research object,and the digestive characteristics of infants were studied by simulating the in vitro gastrointestinal digestive environment of infants.The results showed that the final degree of lipolysis was:HMF>HMFS-G>HMFS-C>HMFS-P;the types of free fatty acids and monoglycerides released by the three human milk replacement fat emulsions during the digestion process were basically the same as those of HMF emulsions.But the released palmitic acid monoglyceride content（48.22%-48.52%）is lower than HMF emulsion（74.43%）,there is no significant difference between the three;combined with the changes in the emulsion particle size,potential and microstructure during the digestion process,it can be seen In the gastric digestion stage,a large amount of flocculation occurred in HMFS-P emulsion,and the flocculation degree of HMFS-C emulsion was the smallest;in the intestinal digestion stage,the flocculation of HMFS-P and HMFS-G emulsions decreased rapidly and gradually stabilized.Keep stable and gradually decrease;the digestion process of HMF emulsion is similar to that of HMFS-C emulsion.