Effect Of Rehydration Properties Of Milk Protein Concentrate On Texture Of High-protein Intermediate Moisture Food System

High-protein intermediate moisture food(HPIMF)is widely used in military,aerospace,snack,sports,nutrition and meal replacement food.The main protein ingredients of HPIMF are whey protein,soy protein,sodium caseinate and milk protein concentrate(MPC).MPC is a kind of novel milk protein ingredient prepared by membrane filtration and spray-drying of skim milk,which mainly contains casein and whey protein(4:1).However,the HPIMF made of MPC is crumbly,hard to be shaped and has both rough taste and bad texture due to the poor rehydration properties of MPC.As the limiting steps in the process of rehydration of MPC are wetting and dispersing,it is possiblely affected by some key factors including the specific surface area,the state of casein micelle and hydrophilicity of the powder particles,this paper focused on the production process of MPC,systematically explored the effects of particle size distribution,state of casein micelle and hydrophilicity of MPC on the molecular migration,microstructure and texture of HPIMF by low-field nuclear magnetic resonance(LF-NMR),confocal laser scanning microscope(CLSM),scanning electron microscope(SEM)and texture profile analysis(TPA),in order to further expand the application of MPC in HPIMFs.The main research contents and results are as follows:Firstly,the particle size of MPC powder was controlled by air flow parameter of spraydrying and then this part studied the effects of particle size of MPC powder on its rehydration property and texture of HPIMF.The results showed that reducing the particle size of MPC could significantly improve its solubility;the molecular migration was faster of HPIMF formulated with small-sized MPC and the system was more stable,continuous and uniform;the small-sized system had a lower increasing rate of hardness and more cohesive texture during storage.These results indicated that reducing the particle size of MPC could partly improve the texture of HPIMF which was more uniform,stable,smooth and cohesive.Secondly,the state of casein micelle was changed after decalcification of retentate of membrane-filtrated skim milk through ion-exchange and then this part studied the effects of decalcification of MPC on its rehydration property,the structure of casein micelle and texture of HPIMF.The results showed that with the increase of decalcification rate,the dissociation level of casein micelle was increased,the solubility of MPC had greatly improved and the texture of HPIMF was more continuous,uniform and cohesive;the small molecule distributions of HPIMF with decalcification rate up to 28.3% had no significant difference and the systems were all continuous and uniform after storage.The results indicated that the HPIMF made of MPC with a decalcification rate of around 28.3% could be uniform and stable and had a good texture which was smooth,moderately hard and very cohesive.Thirdly,the hydrophilicity of MPC was regulated by adding lecithin vesicles to the retentate of membrane-filtrated skim milk.And then this part studied the addition of lecithin vesicles on wettability of MPC and texture of HPIMF.The results showed that the wettability of MPC powder was improved and the molecular migration of HPIMF was faster with the increase of lecithin content and this faster molecular migration could be evident only when lecithin content was up to 6%;the HPIMFs with lecithin content up to 6% were less crumbly and would not fracture after compression and while the lecithin content reached 10%,the hardness of HPIMF was greatly reduced.These results indicated that adding appropriate amount of lecithin could contribute to a more uniform and stable,less crumbly and less hard HPIMF.In summary,the three modification methods of MPC were all beneficial to the optimization of its rehydration properties and had certain effects on a uniform,stable and cohesive texture of HPIMF.And changing the micellar state of MPC by decalcification was the most effective one.It could greatly improve the rehydration property of MPC and the cohesiveness of HPIMF.Adding lecithin to small-sized MPC or to decalcified MPC were also suggested to produce specific MPC powder applied in HPIMF,so as to fully improve the texture of HPIMF.For the HPIMF formulated with lipid,MPC with lecithin could also be used to partially replace the lipid ingredients,so as to improve its texture as well as nutritive value.