| Three different concentrated whole milks (2.5x, 2.75x, and 3.0x) were produced by mixing equal parts of ultrafiltration retentate of whole milk and reverse osmosis retentate of the UF milk permeate. The concentrated whole milks were ultra-high temperature processed by direct steam injection (140.6{dollar}spcirc{dollar}C) followed by flash cooling and two-stage homogenization pressures (2500/500 psi, 3500/700 psi, or 4500/900 psi). The milk concentrates were packaged aseptically and stored at room temperature. On the other hand, the milk concentrates produced by the RO single membrane system with the same concentration levels served as the control. Physicochemical properties of the milks were surveyed every 2 weeks during a 6-month storage period.; The milk concentrates combined from the blending of multiple-membrane retentates showed the expected concentrations of all major nutrients except nonprotein nitrogen. A 20% to 32% shortage of nonprotein nitrogen permeated through the RO membrane during the production of the concentrated whole milks. Over the 6 months' storage, nonprotein nitrogen content did not significantly change in the 2.5x, 2.75x, and 3.0x concentrated whole milks. No microbial growth or enzyme activity was measured or observed in the samples collected. Milk concentrated 2.5x with 4500/900 psi homogenization pressure did not show cream plug formation during the first 5 months of storage. Milk concentrated 3.0x with 4500/900 psi homogenization pressure showed cream plugging at 2.5 months. As higher homogenization pressure was applied, less creaming occurred at all milk concentration levels.; Homogenization at all pressures did not reduce sedimentation during storage. The milk concentrates from the control RO membrane processing showed less sedimentation than did the concentrates from the multiple membrane system at the same homogenization pressure (2500/500 psi). The higher the concentration of total milk solids, the more sedimentation occurred. Viscosity was not affected by homogenization pressure. (Abstract shortened by UMI.)... |
