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This research is aimed at preparing the β-galactosidase (βg) and vitamin C (VC) cocapsules stabilized by milk proteins. The effect of different independent parameters including core-coating ratio (10-100%), whey protein isolate (0 : 1), sodium caseinate (0 : 1), and ultrasound power (50-150 W) on physicochemical properties of microcapsules was investigated. The response surface methodology (RSM) defined the optimal conditions. Increasing the WPI values had different effects on the particle size and polydispersity index (PDI). The zeta potential values decreased by decreasing SC values. The βg had better encapsulation efficiency in comparison to VC. Increasing the core-coating ratio showed a negative effect on the enzyme activity. Among the test parameters, the core-coating ratio was effective on the viscosity of microcapsules. Two optimum conditions for co-encapsulation were determined as WPI, SC, core-coating ratio, and ultrasound power of 0, 1, 100%, and 79.4 W and 0.2, 0.8, 100%, and 75 W for microcapsules I and II, respectively. In the next step, the structural and morphological properties of the optimum samples were analyzed. The heterogeneous morphology of microcapsules was observed by SEM analysis. The formation of new interactions between wall materials, βg, and VC was confirmed by FT-IR analysis. XRD analysis revealed that the WPI-coated sample had a higher crystallinity index. Generally, the successful co-encapsulation of βg and VC exhibited the potential of the resultant microcapsules for the industrial production of VC fortified and lactose-free milk. [ABSTRACT FROM AUTHOR]