Effect Of Human Milk Bile Salt Stimulated Lipase On In-Vitro Milk Lipid Digestion

Human milk is a complex liquid contains complex components needed by infant nutrition.Exclusively breast-fed period is the most crucial time to observe human milk nutrition since the newborns ideally consumed human milk as the single source of energy and nutrition.Beyond macronutrients,human milk also contains minor component including enzyme to overcome immature digestion tract.Bile salt stimulated lipase(BSSL)is an enzyme secreted by mammary gland and found in human milk.It is found to influence the lipid digestion of human milk.In present study,the change of BSSL during lactation,the correlation of BSSL with milk macronutrients,and the effect of BSSL in milk lipid digestion were studied.Proteomics method was used for human milk profiling of 8 different cities during 6 months of lactation.Proteins identified by using proteomics were 860,760,1426,1298,1029,1029,1022,960 in Beijing,Guangzhou,Chengdu,Weihai,Lanzhou,Jinhua,Zhengzhou,and Harbin,respectively.The result showed the high variation of proteins across the cities.The platelet degranulation,innate immune response and triglycerides metabolic process were varied among the cities.Noticable,the intensity of BSSL showed significant decrease especially in the sixth month of lactation which can affect the triglyceride metabolic process.Meanwhile,the pattern of decreasing was varied across the cities.To further explore the change of BSSL during lactation,the exact concentration of BSSL was further investigated in 92 samples of cross-sectional study in Beijing during six months of lactation as well in longitudinal study.Enzyme-linked immunosorbent assay and spectrophotometry-based-lipase activity were used to measure the concentration and activity of BSSL.The result revealed that the BSSL concentration and activity were gradually decreased from the first until six months of lactation.In cross-sectional approach,the BSSL concentration declined during first 6 months of lactation period.The concentration of the first month was 138,56 μg/ml then gradually decreased until 97,07 μg/ml in the sixth month.The similar decreased also happened in longitudinal study that begin with 117,71 μg/ml and end up in 83,71 μg/ml.And both concentration and activity were positively correlated.Furthermore,protein and BSSL concentration also correlated.Meanwhile,no correlation found in BSSL with other macronutrients content in human milk.BSSL concentration and activity were significantly different for boy and girl.Breastmilk for female babies were containing higher activity of lipase enzyme by 2,26 U/ml rather than those for male.There was no remarkable different of macronutrients content during 6 months of lactation in cross-sectional samples.The function of BSSL in digestion was crucial.By 3 hours of in-vitro gastro-intestinal digestion,BSSL in raw human milk resulted in higher free fatty acid compared to pasteurized human milk in which activity of BSSL was lost.Pasteurized human milk(PHM)showed higher monoglycerides as the end product compared to the raw human milk(RHM).The RHM after in-vitro gastro intestinal digestion revealed the absence of triglycerides(TAG)and diglycerides(DAG)left and remaining less than 5% of monoglycerides(MAG).The free fatty acid(FFA)was the dominated product in RHM,the almost similar result also showed in PHM but with more balanced proportion between MAG and FFA.In PHM percentage of FFA 72% and28% MAG.Moreover,short chain free fatty acid was observed as the major product of in-vitro digestion which was easier to be absorbed.In contrast,the absence of BSSL impacted in the long chain fatty acid that might be difficult to be degraded by infant.RHM the dominated MAG was octanoic acid(C8:0)and dodecanoic acid(C12:0)as the major fatty acid in FFA.In PHM,the most abundant fatty acid was C16:1 in FFA and C16:0 in MAG.Visually,the confocal laser scanning microscope demonstrated the presence of BSSL resulted in the smaller lipid particles than the pasteurized one in the same sampling time.