| Milk fat globule membrane(MFGM)is a kind of biofilm wrapped on the surface of milk fat globule(MFG),which has special structure and many functional components.The protection of the MFGM structure in milk or milk powder is considered to have important biological significance.High pressure homogenization will destroy and restructure the MFGM to which the functional proteins is attached.In this study,a new MFGM rich in phospholipids was obtained by adding soybean phospholipids in the homogenization process of milk.The effects on stability of system,membrane protein protection and fat digestibility,as well as its functional application in embedding and protecting fat soluble nutrients such as polyunsaturated fatty acid(PUFA),vitamin E and carotene were studied.This study can provide a reference for the optimization of dairy products.The research contents and results are as follows:(1)The structure,content and composition of lipids in different commercial milk powder were studied and compared with natural human and bovine milk.The results showed that after dissolving,the lipid showed spherical structure;the polar lipid existed as fragments in each milk powder,which was different from that of natural milk.The fluidity data of milk powders were similar with natural milk but the contents of polyunsaturated fatty acids in all milk powder were lower than that in human milk,and higher than that in bovine milk;Due to the destruction of the structure of fat globules in the process of milk powder processing,the polar lipids in three kinds of milk powder did not form membrane structure,which was different from the natural MFGM structure,and the polyunsaturated fatty acids were not enough.Therefore,the protection and optimization of the structure of fat globules,as well as optimization of the fatty acid composition have a certain significance for the current research of dairy products.(2)Before homogenization,soybean lecithin was added to prepare phospholipid-rich homogenized milk(PLM),in order to protect its fat globule structure.The properties of PLM and its fat globule structure were studied,and the spray-dried milk powder was further characterized.The results showed that compared with(HM),PLM had smaller MFG particle size,lower surface potential and higher storage stability.Laser confocal microscopy showed that more surface area of MFG in PLM was covered by phospholipids,similar to that in natural milk.The SDS-PAGE results showed that there were less serum proteins adsorbed on the surface of milk fat globules,and more natural MFGM proteins were preserved.The simulated digestion experiment showed that the digestion process of MFG in PLM was slower than that of HM at the early polymerization stage,but faster at the late depolymerization stage.For milk powder,the addition of phospholipids is not only conducive to the formation of more uniform milk powder particles,but also more uniform MFG in milk powder recovery solution,which is more difficult to aggregate and more complete in structure.Phospholipids participate in the recombination of MFGM in the homogenization process,which changes the structure and properties of the newly formed MFG and plays a good role in improving the properties of homogenized milk and milk powder.(3)The method of adding lecithin was used to improve the phospholipid layer on the surface of homogenized MFG,and the MFG was used to embed and protect three fat-soluble nutrients including fish oil rich in PUFA,vitamin E,and ?-carotene.In general,adding phospholipids can reduce the adsorption of protein on the surface of emulsion,and form particles with smaller diameter,greater absolute surface potential and more stable physical properties.The degree of primary and secondary oxidation in PUFA is slowed down in the process of accelerated storage,and the oxidation loss of vitamin E and ?-carotene was reduced.The above results show that by adding exogenous phospholipids to protect the structure of milk fat globules,it is beneficial to improve its functionality and application value. |
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