Preparation And Digestive Behavior Of Milk Fat Globule Membrane Ingredients

Milk fat globule membrane（MFGM）is a three-layer membrane wrapped around the outside of milk fat globule.The membrane lipids,mainly polar lipids,play an important role in the cognitive and immunity of infants.Recently,foreign dairy enterprises have extracted MFGM ingredients from buttermilk,butterserum and cheese whey,and added them to infant formula to improve the growth and development of infants.However,the composition of polar lipids in MFGM ingredients from different sources is not the same,and the contents of polar lipids in MFGM ingredients vary obviously in different studies because of the complexity and difficulty in measuring phospholipids.In addition,there are few studies on the enrichment process of MFGM ingredients in China,so that the changes of polar lipids in the enrichment process are unclear,and the research on their functional characteristics is also limited.In this study,the compositions of polar lipids in different kinds of commercial phospholipids were studied.The MFGM ingredients rich in phospholipid were separated and enriched from buttermilk powder by membrane filtration,and the difference in vitro digestion between them and soybean lecithin was studied.The main research contents are as follows:Firstly,a method for the analysis of polar lipids in milk was established and commercial products were tested.Phospholipid composition was determined by ³¹P NMR.The limits of detection and quantification of the nine phospholipids were 48.97-85.76μg/m L and 97.94-171.52μg/m L,respectively,with reasonable recoveries（83.40%-108.52%）and precision（standard deviation<15%）.Sterols were determined by gas chromatography-tandem mass spectrometry and ganglioside was determined by ultra-performance liquid chromatography-tandem flight mass spectrometry.The constructed analysis mrthod was used to determine the content and composition of phospholipid,sterols and gangliosides in commercial MFGM ingredients,soybean lecithin and egg lecithin.In terms of total phospholipid content,MFGM ingredients（3.59%-7.95%）were lower than soybean lecithin（55.12%-92.84%）and egg lecithin（37.84%-81.11%）.And sphingomyelin,which was unique in human milk,was only detected in commercial MFGM ingredients.In terms of sterols,the total sterol content of soybean lecithin（1.97-6.12 mg/g）was higher than that of commercial MFGM ingredients（0.62-1.79 mg/g）and egg lecithin（1.45-3.28 mg/g）.Gangliosides were only detected in commercial MFGM ingredients,and the content ranged from 76.47μg/m L to 443.59μg/m L.Secondly,MFGM ingredients with different phospholipid contents were extracted from buttermilk with abundant resources and high yield.The raw materials rich in phospholipids in several dairy processing processes were analyzed.The results showed that the total phospholipid content of buttermilk（19.37-85.39 mg/100m L）was lower than that of butter serum（47.92-113.73 mg/100m L）.The content of phospholipid in buttermilk powder ranged from 0.54%to 0.95%.After removing casein by citric acid coagulation,the total phospholipid content in buttermilk,butter serum and buttermilk powder was increased to 0.31%-1.05%,0.67%-1.42%and 0.65%-1.09%,respectively.Considering the factors of phospholipid content,yield and transportation,buttermilk powder was selected as the raw material for extracting MFGM ingredient.Multistage membrane filtration technology was developed to enrich MFFGM ingredients.The phospholipid content in MFGM ingredients was 1.74%after the first treatment by microfiltration,3.66%after the second concentration by ultrafiltration,and 6.39%after the third concentration by the combination of microfiltration and filtration.Compared with buttermilk powder,the contents of phospholipids,sterols and gangliosides in extracted MFGM ingredient increased from 0.95%,0.19 mg/g and 47.00μg/g to 6.39%,2.45 mg/g and 1026.22μg/g,respectively,and the total fat content increased from 8.89%to 64.22%.The lactose,protein and ash content of extracted MFGM ingredient were reduced from 49.98%to 15.35%,34.02%to 17.18%and 7.12%to 3.25%,respectively.Finally,the difference of digestive properties between the emulsion prepared from soybean lecithin and extracted MFGM ingredient was studied.An oil-in-water emulsion（emulsion 1）with a particle size of 2.62μm simulating the structure of human milk fat globule was prepared by optimizing the homogenization pressure with the emulsifier of the extracted MFGM ingredient.Under these conditions,an oil-in-water emulsion（emulsion 2）with soybean lecithin as emulsifier was constructed.The in vitro system digestive characteristics of two emulsions were studied through the simulation of the infant gastrointestinal digestion.The results showed that after 120 min of simulated digestion,the liolysis degree of emulsion 1 was 85.76%,which was higher than that of emulsion 2（79.25%）,and the relative content of free fatty acids in emulsion 1 was higher at the later digestion stage.Both emulsions keep their fat globule structure in stomach,while the fat globule structure of emulsion 1 was destroyed more completely than that of emulsion 2 in intestine.In summary,an analytical system of polar lipids including sphingomyelin,gangliosides and sterols in milk and dairy products was established,and the composition of polar lipids in commercially products was analyzed.A MFGM ingredient was isolated and enriched from buttermilk powder by membrane filtration,and its in vitro digestion characteristics were verified.This paper provides a theoretical basis for further enrichment of MFGM ingredients from other raw materials,and also promotes the industrial production of MFGM ingredients.