Survival and Reduction of Shiga Toxin-Producing Escherichia coli in a Fresh Cold-Pressed Juice Treated with Antimicrobial Plant Extracts

摘要

This study was conducted to evaluate the survival of 7 Shiga-toxigenic Escherichia coli (STEC) in fresh cold-pressed juice and the antimicrobial efficacy of 4 essential oils (EO: achillea, rosemary, sage, and thyme). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of each EO was determined using microdilution assays evaluated at pH levels 4 and 7; as well as at 4 and 25 ℃; daily for up to 5 d. Results indicated that 5 of 7 serotypes survived well in cold-pressed raw juice for at least 4 d at 4 ℃ and pH 3.5 with no significant (P ＞ 0.05) reduction in viability. The EO showed varying degrees of antimicrobial activity against the 7 STEC. The MIC and MBCs were lowest for thyme (2 μg/L) and highest for sage (15 to 25 μg/L). The antimicrobial activity was enhanced at low pH and temperature. Data showed that although the top 7 STEC could survive low pH and temperature in vitro and in cold-pressed juices, EO, especially from thyme and rosemary, reduced STEC to an undetectable level at 4 ℃, suggesting that they could be used as natural antimicrobials in juice.