| Presently, as the improvement of people’s living and consumption levels, more and more consumers not only pursue the food safety, but also the food quality. For a long time, the technologies of thermal sterilization for cost-effective advantages are widely used in food processing fields. However, the thermal sterilization process can result in many undesirable effects, such as discoloration, off-flavor, and nutritional losses. With the development of science and technology, many technologies of non-thermal sterilization emerged, and are gradually applied into practice. The pulsed magnetic field sterilization is a new developed non-thermal technology and paid more attention. In order to further verify the sterilization performance, the sterilization law of pulsed magnetic field was studied for sterilizing the staphylococcus, and the sterilization mechanism of pulsed magnetic field from the point view of the calcium was evaluated in this research.The growth period of microorganism was an important factor for affecting the sterilization performance of pulsed magnetic field. S aphylococcus in the logarithmic peiiod was more sensitive to the pulse magnetic field than those in the stable vegetal and detention vegetal periods. In addition, the calcium concentration in the logarithmic period increased more than the other two periods. In particular, at the logarithmic period of 10h, the difference of calcium concentration was 105±16nmol/L before and after pulsed magnetic field treatment. The results showed that the staphylococcus had the strongest membrane permeability, and the calcium concentration had the biggest difference before and after pulsed magnetic field treatment in its logarithmic period, which can reasonably explain the phenomenon that staphylococcus had the best sterilization performance in its logarithmic period.The magnetic field strength and pulsed number were primary factors for affecting the sterilization performances of pulsed magnetic field. At the magnetic field strength of 1T,2.5T and 3.5T, the residual rate presented the valley value along with the increase of magnetic field strength. At the magnetic field strength of 3.5T and pulse number of 20, the residual rate was 7.29%, which indicated the best sterilization performance. However, at the magnetic field strength of 2T and 3.5T, the residual rates both increased to peak values, which showed the worst sterilization performance. Staphylococcus was more sensitive to high magnetic field strength at the suitable growth temperatures, and was easily killed. The temperature and pulsed magnetic field had the synergistic effects on sterilization performance, but the temperature increase was lower than staphylococcus’s thermal dead temperature. The changes of calcium concentration were similar to the changes of residual rate. At the magnetic field strength of 1T,2.5T and 3.5T, the calcium concentration reached the highest, which increased from 134±10nmol/L to 287±11nmol/L. However, at the magnetic field strength of 2T and 3T, the calcium concentrations both arrived at the valley values, and increased very little. The changes of regular of [Ca2+]i of staphylococcus were very similar to the changes of residual rate along with the pulsed number, which both appeared the inflection points at the pulsed number of 20. The results showed that the change of calcium concentration was the main reason of different lethal degree of staphylococcus under the pulsed magnetic field at different pulsed numbers.Based on the residual rates of staphylococcus at cultured time of 10h under different processing conditions of pulsed magnetic field, the ideal sterilization conditions were magnetic field strength of 3.5T, pulsed number of 20, temperature of 30℃, and pH 7.0.In this study, the sterilization process of pulsed magnetic field showed the biological window effects, which showed that, at the pulsed number of 20, the window value of magnetic field strength (Iw) conformed to the following computative relation:Iw(n)=n(9-n)/4-1(n was the sequence of strength window, i.e.1,2 and 3). By evaluating the correlation coefficients (R2) of the Gelow, Weibull and Hulsheger models, the results showed that the Gelow model was the best kinetic model to fit the change of residual rate of staphylococcus under pulsed magnetic field. |
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