The US study - Inhibition of Beef Isolates of E. coli O157:H7 by Orange Oil at Various Temperatures – set out to determine the minimum inhibitory concentration (MIC) of the essential oil, cold-pressed terpenless Valencia orange oil (CPTVO) at various temperatures against three strains of E.coli.
The team from the University of Arkansas and Colorado State University found that a 1% solution of the orange oil curtailed growth of E.coli H7:0157 in beef at the chilling stage of processing – and would remain effective if carcasses were exposed to temperature abuse.
The researchers said that E.coli H7:0157 is responsible for around half of the 175,000 cases of shiga toxin producing E.coli in the US annually, citing studies that suggested a wide prevalence of the pathogen present along the beef supply chain.
It noted that, despite action to reduce the number of E.coli outbreaks, incidents still occurred which indicated “additional hurdles during or post-chilling” could help prevent the bacteria entering the food chain.
Methodology and results
In this study, published in the Journal of Food Science, CPTVO examined at 37, 10, and 4C to determine its antimicrobial activity against the trio of E. coli O157:H7 strains recovered from beef products.
The team examined how a range of dilutions of the essential oil - ranging from 0.2% to 25% or 0.1% to 10% performed. Plates were incubated at the three temperatures were and sampled hourly.
They found after 6 h at 37C, all strains were inhibited at concentrations ranging from 0.2% to 0.6%, with a mean of 0.4 ± 0.01%.
At 10C, all strains were inhibited at concentrations ranging from 0.8% to 6.3%, with a mean of 1.1% ± 0.2%, after 6 hours.
At 4C, all strains were inhibited after 6 hours at concentrations ranging from 2.3% to 4.6%, with a mean of 3.5% ± 2.1%.
After 24 hours at 4C the strains were inhibited at concentrations ranging from 0.7% to 1% with a mean of 0.8% ± 0.3%.
Temperature and pH key parameters
In common with previous research, the study noted a decrease in the activity of the CPTVO at lower temperatures. Efficacy was also dependent on the E.coli strain employed – with a three-fold decrease of activity for only one of the strains and less than a two -fold decrease for the other strains.
They concluded that parameters such as temperature, pH influence essential oil antimicrobial activity and a full analysis to develop a complete understanding of the how the oils react with foods that have differing physic/ chemico properties would need to be carried out.
But the team said its findings pointed to its research could have application in the beef industry where carcasses are chilled to close to (or at) 4C within 24 hours.
"Our results indicate that a solution of 1% cold pressed terpeneless Valencia orange oil could be used as an additional intervention against E. coli O157:H7 at the chilling stage of processing, and will remain effective if the carcasses are subjected to temperature abuse,” said lead author Phillip G Crandall.
The team also highlighted the need to screen multiple strains of the same species or serotype when examining essential oils.
Inhibition of Beef Isolates of E. coli O157:H7 by Orange Oil at Various Temperatures by Sean J. Pendleton, Philip G. Crandall, Steven C. Ricke, Lawrence Goodridge, and Corliss A. O’Bryan; published in the Journal of Food Science; doi: 10.1111/j.1750-3841.2012.02689.x