Combined effect of ultrasound and selected essential oil constituents on Escherichia coli O157:H7 and Listeria monocytogenes reduction in orange juice

Abstract

The purpose of this study was to determine the combined effects of 20 kHz ultrasound (US) and selected essential oil (EO) constituents (eugenol, linalool and cinnamaldehyde:200, 400, 800 and 1000 µl/l) on the reduction of Escherichia coli O157:H7 and Listeria monocytogenes in orange juice (OJ) at different temperatures. Combined effect of citric acid and US on the reduction of test bacteria was also determined. All ultrasonic treatments were applied at 80% amplitude (99.2 µm intensity). After 5 min of ultrasonic treatment, E. coli O157:H7 (at 45°C) and L. monocytogenes (at 50°C) numbers were decreased by 1.3 log cycles in OJ samples. US in combination with EO constituents reduced the viability of E. coli O157:H7 and L. monocytogenes. If sonication (at 45°C) was combined with eugenol or linalool (1000 µl/l), E. coli O157:H7 numbers were decreased by5.92 and 5.85 log cycles, respectively, in <30 s. Similarly, if sonication (at 50°C) was combined with eugenol or linalool (1000 µl/l) L. monocytogenes numbers were decreasedby 5.53 and 5.71 log cycles, respectively. Cinnamaldehyde and citric acid were the least active compounds for inhibiting test bacteria compared with the other two compounds. Moreover, no microbial growth in OJ samples treated with US and EO constituents (1000µl/l) was observed during 48 days of storage at 4 and 25°C. Key words: Ultrasound, bacterial inactivation, Eugenol, Linalool, Cinnamaldehyde.