Abstract: The article studied the killing effects of Instantaneous High Pressure on Bacillus stearothermophilus considering different pressures, times of dealing and the influences of the food substances. The results of the experiments were as follows. ①Instantaneous High Pressure has better effects on killing Bacillus stearothermophilus. With the increase of pressure, the killing rate of Bacillus stearothermophilus increases, but the killing rate of Bacillus stearothermophilus increases a little with the increase of feed-in temperature. When dealing at the temperature 10, 25 and 40℃ respectively for once every time, and with the pressure rising from 80MPa to 120MPa, the killing rate increases from 54.13%, 53.81% and 54.39% to 74.12%, 74.52%, 74.96% respectively. ②With the increase of dealing time, the killing rate of Instantaneous High Pressure on Bacillus stearothermophilus also increases, and the result is more satisfactory with the increase of the dealing times instead of the pressure. Under 25℃, when the pressure of 100, 110 or 120MPa is applied respectively to the sample treated from one to three times respectively, the killing rate of 100MPa is respectively 67.6%, 74.13% and 77.95%; that of 110MPa 71.34%, 76.89% and 80.74% respectively and that of 120MPa 74.52%, 79.58% and 82.08% respectively. ③Food matrix can protect the bacteria from the treatment of Instantaneous High Pressure. To certain concentration, the higher the concentration of food matrix is, the stronger the effect of bacteria-protection. For instances, the disinfected soy milk was added to the bacteria liquid, with different concentrations as 0, 1.5, 3, 4.5 and 6g/100g respectively, while the bacteria was treated with Instantaneous High Pressure with the feed-in temperature 25℃ and the work pressure 100, 110 and 120MPa respectively. The results showed that the killing rates of Bacillusstearothermophilus dropps from 67.6% to 65.73% under 100MPa, from 71.34% to 69.12% under 110MPa and from 74.52% to 72.36% under 120MPa.

Key words: Instantaneous High Pressure(IHP), Bacillus stearothemophilus, food matrix