Combined effect of shear stress and moderate electric field on the inactivation of Escherichia coli K12 in apple juice

The effectiveness of combined shear stress (SS) and moderate electric field (MEF) on the inactivation of Escherichia coli K12 in apple juice was investigated. Inoculated samples were treated at two temperatures (40 degrees C and 50 degrees C) for various times (up to 30 min) by this combined treatment (shear rate: 151.5-2879 s(-1); electric field strength: 0-120 V/cm). Bacterial reduction resulting from shear and MEF combination was significantly different (p < 0.05) from that resulting from conventional heating and individual treatments at both temperatures. The highest lethal rate (5.62 +/- 0.44 log reduction in 7.5 min) was obtained for samples treated with a combination of 2879 s(-1) shear rate and 120 V/cm MEF at 50 degrees C. The optimum process parameters for a 5-log cycle reduction of E. call K12 were obtained using response surface methodology. The combination process at 50 degrees C resulted in no significant effect on pH, color, and free-radical scavenging of apple juice.