Effect of ultrasound and low-intensity electrical current for microbial safety of lettuce

Abstract

In this study, we aimed to use ultrasound and low-intensity electrical current practices to make lettuce safer for human health. For this purpose, three electric currents (0.2, 0.8, and 1.4 mA) and two ultrasonic processes (24 and 40 kHz), used both separately and simultaneously, were applied to the lettuce leaves at five treatment time (2-10 min). At the first stage, the effects of these processes on the microbiota of the fresh lettuce leaves were investigated. Therefore, the TMAB, the total coliform, the total yeast&mold were determined as 5.94 +/- 0.20, 5.65 +/- 0.27, and 4.82 +/- 0.33 log cfu/g, respectively. After the processes, the maximum inactivation rates were determined as 2.891og, > 3log, and 2.98log, respectively. While there was no dramatic change in physicochemical properties of lettuce; the free chlorine and hydrogen peroxide contents increased with the time in the process water. At the second stage, the effects of these processes on pathogens were investigated. 6 log of E.coli O157:H7, L.monocytogenes and, S.aureus were inoculated to the lettuce samples and was treated by the processes. The pathogenic microorganisms in the lettuce samples were inactivated up to 4.05, 3.12, and 2.84 log cfu/g, respectively. In the model system, the pathogens couldn't be detected after 6, 8 and 4 min, respectively.