The Production Of Milk Protein Concentrate And The Application In The Stirred Yogurt

Milk protein concentrate (MPC) is a high protein spray-dried powder manufacturedfrom skim milk by means of membrane separation. MPC contains high concentrations ofprotein and calcium and low concentrations of lactose. The proportion of casein and wheyin MPC is just same as the raw milk. MPC could be used in a wide range of products. MPChas relatively poor solubility for their high protein content. For most applications, MPC hasto be dissolved back into water, since the powder material does not fully express itsfunctional properties if it remains insoluble, a true solution and/or complete dispersion ofcolloidal particles is required.In our study, the effect of spray-drying temperature and evaporation process on thefunctionality of MPC80was reported, also the manufacturing process of MPC80wasoptimized. The optimized process included treating the retentate of ultrafiltration bydifferent ultrasonic time or adding several kinds of chelating agents to the retentate prior tospray-drying. Finally, we compared the characteristic of stirred yogurt fortified with MPC80and other kinds of milk proteins such as SMP, WPC and CS. The whole research couldprovide some support for the production and application of MPC in industry. The mainconclusions of all the research were as follows:(1) The solid content of milk retentate was about15.55％after membraneulrafiltration, which could be improved to18.17％and26.12％by evaporation. As thesolid content of milk retentate increased from15.55％to26.12％, particle size of theMPC80also increased from20.62μm to33.17μm, but moisture content decreased from4.59％to3.85％. There was no significance variation for solubility of all samples (P＞0.05). Some physical properties of self-made MPC80were not as much better ascommercial MPC85, such as the apparent density, tap density and degree of compression.However, all these physical properties were improved for the higher solid of milk retentate.(2) The effect of different spray-drying temperature (130,160and190℃) on thefunctionality of MPC80have been reported. The results showed that there was nosignificant variation for whey protein denaturation (P＞0.05). The moisture content andsolubility decreased as a function of spay-drying temperature. It could be speculated fromthe SDS-PAGE profile that the mainly insoluble protein was casein. All of whey protein were soluble, especially β-lactoglobulin which was very stable. Considering bothfunctionality of MPC and economic cost, we choosed the outlet and inlet temperature were60℃and130℃, respectively.(3) It was found that there was a particle size reduction with sonication for0.5min (P＜0.05). The H0of reconstituted MPC80solution increased significantly as a function ofsonication time. Solubility increased from35.78％to88.30％after ultrasonic for5min.Ultrasound-treated samples presented higher elastic character than the control all along themeasurement, which can be attributed to a stronger aggregation promoted by thehydrophobicity due to sonication. The SDS-PAGE profile of the samples showed that thebands of the control were just same to the ultrasonicated samples. This observationconfirmed that the molecular weight of the proteins is not changed by sonication.The particle size of MPC80decreased after adding different kinds of chelating agents,but the H0increased for the change of casein micelle structure. The solubility ofreconstituted MPC80manufactured with added sodium citrate, sodium pyrophosphate andtrisodium phosphate increased significantly. The improvement of solubility could beattributed to the change of H0and electric charge density. The viscosity of MPC80solutionalso increased.(4) Milk supplementation with milk proteins in four different levels was used toinvestigate the effect on the acidification and textural properties of yogurt. The resultsshowed that fermented time of yogurt has been prolonged for all the milk proteinsupplementation. After fermentation, the yogurts made with milk supplemented resulted insignificant properties changes, which were increase in water capacity and viscosity. Afterstoring at4℃for1,7and14d, it was observed that the viscosity of all the samples decreased,but there was no significant change for the water capacity. The results of sensory analysisshowed that the flavor of yogurts fortified with MPC and SMP was improved. Themicrostructure of the samples was screened by the scanning electron microscopy technique.Scanning electron microscope images of the probiotic yogurt samples differed because ofthe addition of dairy proteins.