Sobrino-López Angel, Martín-Belloso Olga
Department of Food Technology, University of Lleida, Spain.
J Food Prot. 2006 Feb;69(2):345-53. doi: 10.4315/0362-028x-69.2.345.
High-intensity pulsed electric fields (HIPEF) can be used as a nonthermal preservation method that is believed to enhance the effect of nisin on microorganisms such as Staphylococcus aureus. The survival of S. aureus inoculated into skim milk and treated with nisin, with HIPEF, or with a combination of nisin-HIPEF was evaluated. Nisin dose, milk pH, and HIPEF treatment time were the controlled variables that were set up at 20 to 150 ppm, pH 5.0 to 6.8, and 240 to 2,400 micros, respectively. HIPEF strength and pulse width were kept constant at 35 kV/cm and 4 micros, respectively. No reduction in S. aureus concentration was observed in skim milk at its natural pH after treatment with nisin, but 1.1 log units were recovered after 90 min of treatment at pH 5.0 with 150 ppm nisin. A reduction in viable S. aureus counts of 0.3 and 1.0 log unit in skim milk treated with HIPEF at its natural pH was observed at 240 and 2,400 micros, respectively. The nisin-HIPEF treatment design was based on a response surface methodology. The combined effect of nisin and HIPEF was clearly synergistic. However, synergism depended on pH. A maximum microbial inactivation of 6.0 log units was observed at pH 6.8, 20 ppm nisin, and 2,400 micros of HIPEF treatment time, whereas a reduction of over 4.5 log units was achieved when pH, nisin concentration, and HIPEF treatment times were set at 5.0, 150 ppm, and 240 micros, respectively.
高强度脉冲电场（HIPEF）可作为一种非热保鲜方法，据信该方法能增强乳酸链球菌素对诸如金黄色葡萄球菌等微生物的作用效果。对接种到脱脂乳中并分别用乳酸链球菌素、高强度脉冲电场或乳酸链球菌素 - 高强度脉冲电场组合处理的金黄色葡萄球菌的存活率进行了评估。乳酸链球菌素剂量、牛奶pH值和高强度脉冲电场处理时间是控制变量，分别设定为20至150 ppm、pH 5.0至6.8以及240至2400微秒。高强度脉冲电场强度和脉冲宽度分别保持恒定在35 kV/cm和4微秒。在用乳酸链球菌素处理后，天然pH值的脱脂乳中未观察到金黄色葡萄球菌浓度降低，但在pH 5.0、150 ppm乳酸链球菌素处理90分钟后，金黄色葡萄球菌浓度回升了1.1个对数单位。在天然pH值下，分别在240和2400微秒时，观察到用高强度脉冲电场处理的脱脂乳中金黄色葡萄球菌活菌数分别减少了0.3和1.0个对数单位。乳酸链球菌素 - 高强度脉冲电场处理设计基于响应面法。乳酸链球菌素和高强度脉冲电场的联合作用具有明显的协同性。然而，协同作用取决于pH值。在pH 6.8、20 ppm乳酸链球菌素和2400微秒的高强度脉冲电场处理时间下，观察到最大微生物失活为6.0个对数单位，而当pH值、乳酸链球菌素浓度和高强度脉冲电场处理时间分别设定为5.0、150 ppm和240微秒时，微生物减少超过4.
