Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture(1), Wyndmoor, Pennsylvania 19038, USA.
Int J Food Microbiol. 2010 Mar 31;138(1-2):50-5. doi: 10.1016/j.ijfoodmicro.2010.01.004. Epub 2010 Jan 14.
Radio frequency electric fields (RFEF) and UV-light treatments have been reported to inactivate bacteria in liquid foods. However, information on the efficacy of bacterial inactivation by combined treatments of RFEF and UV-light technologies is limited. In this study, we investigated the relationship between cell injury and inactivation of Escherichia coli K-12 in apple juice treated with a combination of RFEF and UV-light. Apple juice purchased from a wholesale distributor was inoculated with E. coli K-12 at 7.8 log CFU/ml, processed with a laboratory scale RFEF unit at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min followed by UV-light treatment (254 nm) for 12s at 25, 30 and 40 degrees C. Treated samples were analyzed for leakage of UV-substances as a function of membrane damage and were plated (0.1 ml) on Sorbitol MacConkey Agar (SMAC) and Trypticase Soy Agar (TSA) plates to determine the viability loss and percent injury. At 40 degrees C, UV-light treatment alone caused 5.8 log reduction of E. coli in apple juice while RFEF caused only 2.8 log reduction. A combination of the two processing treatments did not increase cell injury or leakage of intracellular bacterial UV-substances more than that from the UV-light treatment. Similarly, the viability loss determined was not significantly (P<0.05) different than UV-light treatment alone. However, the UV-substances determined in apple juice treated with RFEF was significantly (P>0.05) different than UV-light treated samples. The results of this study suggest that RFEF treatment causes more injury to the bacterial cells leading to more leakage of intracellular UV-substances than cells treated with UV-light alone. Also, the effect of the two processing treatment combination on bacterial inactivation was not additive.
射频电场（RFEF）和紫外光处理已被报道可使液体食品中的细菌失活。然而，关于射频电场和紫外光技术联合处理对细菌失活效果的信息有限。在这项研究中，我们研究了射频电场和紫外光联合处理对苹果汁中大肠杆菌 K-12 的细胞损伤和失活的关系。从批发商处购买的苹果汁以 7.8logCFU/ml 的浓度接种大肠杆菌 K-12，以 540ml/min 的流速在实验室规模的射频电场单元中用 20kHz、15kV/cm 处理 170μs，然后用紫外光（254nm）处理 12s，处理温度分别为 25、30 和 40°C。用紫外吸光物质的渗漏来分析处理样品作为膜损伤的函数，并在 Sorbitol MacConkey Agar（SMAC）和 Trypticase Soy Agar（TSA）平板上（0.1ml）平板培养来确定失活率和损伤百分比。在 40°C 时，单独的紫外光处理使苹果汁中的大肠杆菌减少了 5.8log，而射频电场只减少了 2.8log。两种处理方法的联合处理并没有比单独的紫外光处理更增加细胞损伤或细胞内细菌紫外吸光物质的渗漏。同样，确定的失活率与单独的紫外光处理没有显著差异（P<0.05）。然而，在经过射频电场处理的苹果汁中确定的紫外吸光物质与经过紫外光处理的样品显著不同（P>0.05）。这项研究的结果表明，与单独用紫外光处理的细胞相比，射频电场处理对细菌细胞造成的损伤更大，导致细胞内紫外吸光物质的渗漏更多。此外，两种处理方法联合处理对细菌失活的效果不是相加的。
