Abstract:

Effect of ultra-high pressure sterilization technology on the qualities of fresh raw milk was studied. Fresh raw milk was subjected to UHP treatment (continuous, alternative pressure treatment and hurdle technology) at selected pressure (350 to 600 MPa) for various holding times. Pressure treated samples were enumerated to determine the residual microbial population and initial counts were obtained from the control samples. The changes of nutrition in milk treated with different technologies are also deterimined. Resilts showed that:(1) Higher pressure, longer holding time and more alternative times favour a larger destruction of microorganisms; (2) The combined effect of barrier (fence) technology and pressure on the destruction of microorganisms in fresh raw milk is more effective than that of only pressure treatment, and the effect of ε -polylysine on inactivation of microorganism in fresh raw milk is more effective than that of Nisin at the same concentration of 100 mg/L; (3) Compared with the SDS-PAGE electrophoretogram of whole proteins in fresh raw milk, the first bands near the negative pole of those in milk treated with different sterilization ways disappear and the colour of the second bands has slight loss, which suggests that subunits of some proteins are dissociated, but the 400 MPa-treated milk shows the similar eletrophoretogram with the fresh raw milk; (4) The loss of threonine, VA and VC in high pressure-treated milk is much less than those in pasteurism-treated milk, in particular threonine and VA are almost retained, and the contents of VB1 and VB2 in the former also more than that in the latter; (5) High pressure-treated milk has longer shelf life than pasteurism-treated milk, extending the sale semidiameter of products.

Key words: ultra-high pressure, fresh raw milk, total count of bacteria, hurdle technology, nutrition