Effects of pressure, shear, temperature, and their interactions on selected milk quality attributes

The effects of pressure, temperature, shear, and their interactions on selected quality attributes and stability of milk during ultra-shear technology (UST) were investigated. The UST experiments include pressure (400 MPa) treatment of the milk sample preconditioned at 2 different initial temperatures (25 degrees C and 15 degrees C) and subsequently depressurizing it via a shear valve at 2 flow rates (low: 0.15-0.36 g/s; high: 1.11-1.22 g/s). Raw milk, high-pressure processed (HPP; 400 MPa, similar to 40 degrees C for 0 and 3 min) and thermal treated (72 degrees C for 15 s) milk samples served as the controls. The effect of different process parameters on milk quality attributes were evaluated using particle size, zeta potential, viscosity, pH, creaming, lipase activity, and protein profile. The HPP treatment did not cause apparent particle size reduction but increased the sample viscosity up to 3.08 mPa.s compared with 2.68 mPa.s for raw milk. Moreover, it produced varied effects on creaming and lipase activity depending on hold time. Thermal treatment induced slight reduction in particle size and creaming as compared with raw milk. The UST treatment at 35 degrees C reduced the effective diameter of sample particles from 3,511.76 nm (raw milk) to 291.45 nm. This treatment also showed minimum relative lipase activity (29.93%) and kept milk stable by preventing creaming. The differential effects of pressure, shear, temperature, and their interactions were evident, which would be useful information for equipment developers and food processors interested in developing improved food processes for dairy beverages.

Automated summary

The study investigated the effects of pressure, temperature, shear, and their interactions on milk quality during UST, revealing that pressure treatment increased viscosity and thermal treatment slightly reduced particle size and creaming. UST treatment at 35 degrees Celsius effectively reduced particle size, decreased lipase activity, and prevented creaming in milk, showcasing the differential effects of pressure, shear, and temperature interactions for potential food process improvements.