Effects Of Casein Micelle And Decalcification On Milk Protein Concentrates Applied As Wall Material

Milk protein concentrates(MPCs)are a series of new dairy products with high protein content and manufactured by spray drying of skim milk after its lactose is partly removed through ultrafiltration.MPC own superior functionalities and good nutritional value.Compared to traditional milk protein ingredients such as whey protein concentrates/insolates(WPC/WPI)and sodium caseinate(SC),the production process of MPC is simpler and the cost is relatively cheap.However,owing to the limitation of membrane filtration technology,the appearance of MPC is late which lead to few applications nowadays.This study investigated the possibility of MPC applied in the field of microcapsules.With the conjugated linoleic acid(CLA)as model core material,the embedding and protective effects of MPC as wall material were researched.The effect of main protein structure(Casein micelle structure)in MPC was also been found.On this basis,the casein micelles in MPC were further destroyed by decalcification treatment trying to improve the deficiencies.The main research content and conclusions were as follows:(1)MPC-CLA microcapsules were prepared by using MPC as the wall material and conjugated linoleic acid(CLA)as core material.By comparison with WPC80(reported wall material with high quality)and WPI+SC(mass ratio of 1?4,the mixture has the same protein as MPC but without casein micelle structure),the embedding and protection effects of MPC on CLA were investigated and the effect of casein micelle structure was also figured out.The results showed that the presence of casein micelles induced larger size and wider distribution of oil droplets in the MPC-CLA emulsion,more dents on the microcapsule surface and cracks inside.The deterioration of CLA encapsulated by MPC during storage was observed,which is faster than groups of WPI+SC and WPC80.(2)A series of decalcified MPC solutions were achieved by ion exchange process with casein micelle inside changed,which were further used as wall materials.Size distribution and TEM showed that when the decalcification rate was 14.0%,the micelles partially dissociated and the surface became rough;At the decalcification rate of 28.0%,most casein micelles dissociated and free proteins gathered or tangled to form filamentous aggregates;When the decalcification rate increased to 45.2% and 59.2%,the micelles were completely dissociated and the distribution of protein is uniform.(3)CLA microcapsules were prepared with MPCs of different decalcification rates as wall materials.It was found that with decalcification rate increased,the microencapsulation efficiency was improved,the surface indentation of microcapsules decreased and the shell became denser.It is particularly necessary to point out that the decalcification rate is not single positively related to the embedding and protection effect of microcapsules.When the decalcification rate was relatively low(e.g.,14.0% and 28.0%),the oil droplets either in emulsions or later obtained microcapsules were bigger and easier to aggregate,when compared to the untreated MPC group.The oxidation rates were also higher during storage.However,when decalcification rate were relatively high(e.g.,45.2% and 59.2%),the oil droplets in emulsions and microcapsules became smaller and evenly distributed.The oxidation speed is relatively lower but still higher than the WPI+SC group.In summary,as a relatively new protein ingredient,MPC has potential application value in the field of wall materials.But the existence of casein micellar structure adversely affects the utilization.Ion exchange decalcification can effectively destroys the structure of casein micelle in MPC.The low decalcification degree cannot improve the embedding effects,but contrarily accelerates the oxidation of the core.Only higher decalcification degree(more than 45%)have positive effect to MPC as wall materials.