| Human milk is the direct source of energy intake in infants and young children,but in most cases,breastfeeding is difficult to achieve,infant formula milk powder as a substitute for human milk has been widely concerned.At present,the types of infant formula milk powder are gradually diversified with the needs of the market.Protein is the main component of infant formula milk powder,but there are differences in the types and content of protein in milk powder for different infant groups.For example,for the allergic reaction of infant feeding milk powder,hydrolyzed protein formula can replace regular formula milk powder,so as to reduce the allergic reaction of the infant group with milk protein allergy.As the main protein type in milk powder,whey protein contains more than 50%of the total protein.However,current studies mainly focus on the emulsifying and nutritional properties of whey protein.It is not clear how the types of whey protein in different milk powder products affect the formation of milk powder and the digestion and absorption of nutrients.In this paper,the milk powder whey protein concentrate（WPC）,whey protein rich in milk fat globule membrane phospholipid（MPL）,moderately hydrolyzed whey protein（MHP）and highly hydrolyzed whey protein（HHP）were used as research objects to prepare protein-stable emulsions,and to explore the effects of different milk powder whey protein on the formation and related characteristics of the emulsion.At the same time,different protein emulsions were prepared into microcapsules by spray drying technology,and the powder characteristics of different protein microcapsules were analyzed.The in vitro digestion model was used to study the digestion characteristics of different protein emulsions and microcapsules loaded withβ-carotene,and to explore the effects of different types of whey protein on the digestion and absorption characteristics of nutrients.The main conclusions are as follows:1.Influence of protein type of milk powder whey on emulsion formationExplore the influence of different oil phase content and different protein concentration on the formation and basic properties of emulsion.With different protein solutions as water phase and soybean oil as oil phase,the emulsion systems were constructed according to different oil-water ratios,and the basic characteristics of the emulsion were characterized.By changing the environmental stress,such as storage temperature,ionic strength,p H and storage time,the influence of environmental stress on emulsion stability was investigated.The results showed that with the gradual increase of oil content,the particle size of each emulsion showed an increasing trend,and with the increase of proteolysis degree,the particle size of MHP and HHP emulsions basically maintained at the micron level.Under different protein concentrations,the particle size of each emulsion decreased with the increase of protein concentration,and its stability also improved.During the 28-day storage period,the emulsion with 0.5%protein stability broke at the later stage of storage,while the emulsion with other protein concentrations remained stable,and the particle size did not increase significantly.By changing the environmental conditions,it was found that the protein-stabilized emulsion particles were stable to aggregation under low and high p H,and the particle aggregation was obvious when the p H was close to the isoelectric point of protein.The change of ionic strength had no significant effect on the particle size and microstructure of the emulsion.Under the heating condition,no obvious particle aggregation phenomenon occurred in the WPC emulsion,MPL and MHP stable emulsion,and HHP emulsion always maintained a large particle size aggregation state.2.Influence of milk powder whey protein type on microcapsule formationWith the protein content of 5%and 5%of the oil phase content in the preparation of the emulsion,and the preparation of microcapsule by spray drying technology,to explore the different types of whey protein on influence the formation of microcapsule,and further using the microcapsule of fat-soluble nutrients beta carotene load,the characterization of microcapsules after dissolving properties,microstructure and microcapsule interfacial protein adsorption rate and the encapsulation rate index.The results showed that different kinds of protein microcapsules all maintained 5%～7%water content,and the porosity of microcapsules was different.In the blank microcapsules,the particle size distribution of the original emulsion and powder redissolved emulsion was compared.Except for MHP microcapsule emulsion,the particle size of WPC,MPL and HHP microcapsules remained at the nanometer level after redissolved,and the interface protein adsorption rate of each microcapsule after redissolved was higher than that of the initial emulsion.Compared with WPC microcapsules,the redissolution rate and encapsulation rate of MHP and HHP microcapsules were significantly reduced.The microstructure of the microcapsules containingβ-carotene after redissolution was similar to that of the blank microcapsules.Scanning electron microscopy results showed that there were significant structural differences between the MHP and HHP blank microcapsules and the correspondingβ-carotene microcapsules,which also explained the obvious differences in encapsulation rate and porosity between the two microcapsules.3.Influence of whey protein types onβ-carotene absorption characteristics of milk powderUsing the emulsions and microcapsules containingβ-carotene as carriers,the digestion and absorption characteristics of nutrients by different proteins were explored,and compared with the commercial conventional formula milk powder.Meanwhile,the basic characteristics and digestion behavior of the emulsions during digestion were characterized.The results showed that different protein emulsions showed different structural changes during digestion,among which MPL and MHP could significantly reduce the accumulation of oil during stomach digestion.The microcapsule digestion behavior was similar to that of emulsion,and the aggregation of MPL microcapsule in stomach was less than that of commercial milk powder.The bioaccessibility ofβ-carotene in different protein emulsions and microcapsules was compared.The bioaccessibility ofβ-carotene in different protein substrates and different encapsulated dosage forms was different.The bioaccessibility ofβ-carotene in the four protein emulsions was MPL（51.89±2.94）%b>MHP（46.45±0.40%）bc>HHP（44.49±0.92）%ac>WPC（42.58±2.24）%a.The bioaccessibility ofβ-carotene in four microcapsules was MPL（77.50±0.78）%b>MHP（74.53±1.14%）c>WPC（72.97±1.02）%ab>HHP（70.69±0.08）%a,The bioaccessibility of MPL emulsion and microcapsule was significantly higher than that ofβ-carotene encapsulated in other proteins. |
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