Inactivation of Bacillus subtilis by Pulsed Magnetic Field Combined with Temperature, Ultrasonic, and Nisin
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Abstract:
The effect of pulsed magnetic field (PMF) with the intensity of 3T and 30 pulses combined with temperature (50~100 ℃), ultrasonic (200 W, 5~30 min), and nisin (100~350 IU/mL) on the inactivation of Bacillus. subtilis (B.subtilis) was investigated. The results showed that after pretreated by PMF, the survival rate decreased with the increase of the temperature, ultrasonic power and the nisin concentration, and the lowest survival rate (3.17%) was achieved when B. subtilis were treated by PMF followed by the temperature at 100 ℃. The survival rate decreased with the the increase of treatment time by ultrasonic and the lowest survival rate of 8.18% was obtained when B. subtilis were treateded by PMF followed by ultrasonic at the power of 200 W with working time of 5 s and the interval of 10 s for 30 min. Increase in concentration of nisin led to the reduce of survival rate of B. subtilis. The combined treatments of PMF followed by nisin at 350 IU/mL exhibited a lowest survival rate of 19.21%. The inactivation effect was better when B. subtilis were treated by PMF followed by temperature, ultrasonic, and nisin than treated by temperature, ultrasonic, and nisin followed by PMF, which was in agreement with the phenomenon observed by the SEM. The morphology of B. subtilis changed and the cells shrunk after the combined treatments. The release of cytoplasmic contents of B. subtilis occurred after the treatments of PMF followed by nisin.
