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

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 °C; 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 °C 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 °C, suggesting that they could be used as natural antimicrobials in juice.

Raw organic cold-pressed juices are becoming popular in North America due to their claimed health benefits. The safety of these products relies mainly on low temperature and pH. However, some foodborne pathogens can survive these hurdles. The paper provides new data on the growth and survival of Shiga-toxigenic Escherichia coli in raw cold-pressed juice and essential oils with potential as natural antimicrobials. Information presented will help small producers to evaluate the food-safety risk associated with raw cold-pressed juice products.