Abstract:

Pulsed pressure caused by the continuous high-pressure jet of reciprocating pump was applied to treat raw milk for sterilization. The effects of feed temperature, pressure and treatment time on the activity of lactoperoxidase in raw milk were investigated by single-factor and quadratic orthogonal rotation combination design methods. When raw milk was pressurized at 40－ 80 MPa for 4 min at 35 ℃, the activity of lactoperoxidase elevated significantly. While at the same temperature, pressure treatment at 60 MPa for 2－8 min led to sustained marked decline of the activity of lactoperoxidase (P ＜ 0.05). The highest activity of lactoperoxidase was attained by instantaneous 20 MPa pressure treatment at 45 ℃. The significant sequence of the three factors affecting the activity of lactoperoxidase (Y) was as follows: feed temperature (A) > pressure (B) > treatment time (C) and all these factors had a significant interaction effect, which could be described by a regression equation: Y = 62.70－9.43A2－7.96B2 + 3.44C2.

Key words: raw milk, instantaneous high-pressure, medium temperature, lactoperoxidase, activity