Functional properties of skim milk processed with continuous high pressure throttling

The objective of this project was to evaluate the functional properties of continuous high pressure throttled milk. Milk was obtained from the University of Georgia dairy farm and separated. Skim milk (9% solids) was divided, and one-half of the volume was concentrated by ultrafiltration to 18% total solids. Samples of concentrated and unconcentrated milk were subjected to treatment with 310 MPa (4:5,000 psi) of pressure by a process of continuous high pressure throttling for a maximum of 0.3 s or were not pressure treated. All milk samples were chilled to 4 degrees C following treatment and then evaluated for functional properties. Only pressurized milks (9 and 18% solids) produced stable foams. The emulsion stability index, measured at 6-h intervals for 24 h, was lower for the pressurized concentrated milk samples, but pressure treatment produced more stable emulsions in unconcentrated milk. Pressure had no significant effect on interfacial tension. Values for surface tension were higher for pressurized milk samples. Pressurized milks were more viscous. Lightness (L*), greenness (a*), and blueness (b*) were affected by pressure treatment in unconcentrated milk; pressurized milks had lower L* (less white), a* (greener), and b* (bluer) values than the unpressurized milks. In concentrated milk, pressure treatment imparted greener color only. Creamers made with pressure throttled milk samples (both systems) were stable (i.e., did not exhibit feathering) when added to coffee solutions.