By Jess Halliday, 13-Mar-2008
Citrus oils – particularly those already used as flavourings – could be an ideal alternative to chemical-based antimicrobials for food applications, says a new paper.
The tide is currently turning against chemical-based bactericides for food use, opening up opportunities for alternatives from natural sources. The reasons for this are manifold and include general consumer preferences for natural foods, legislative changes, and the isolation of antibiotic resistant pathogens.
Katie Fisher and Carol Philips of the University of Nottingham’s School of Health, UK, believe that citrus essential oils (EOs) show strong potential to be used instead, not least because they are already recognised as safe and have already been seen to have an inhibitory affect against both gram-positive and gram-negative bacteria.
In a review of the evidence to support this use published in Trends in Food Science and Technology, the researchers looked at the body of evidence to recommend their use, noting that the antimicrobial properties of citrus EOs have only started to be explored quite recently.
However in order for their use to be considered in all seriousness, there are certain limitations that need to be bourn in mind.
Fisher and Philips note that there is some evidence that they could kill off other organisms in the human gastrointestinal tract – not just unhelpful bacteria.
“Should EOs be applied to food they may be able to inhibit a wide range of organisms, but they could also cause an imbalance in gut microflora,” they wrote.
Thus, while more research is conducted on the effect of certain EOs throughout the whole intestinal tract, they recommend that a good starting point for the food industry would be to look at using those citrus oils that are already being used as food flavours.
This would include the likes of orange, lemon, lime and grapefruit.
The flip side of this, however, is that citrus EOs can affect the organoleptic properties of a foodstuff.
“Finding an oil/component/vapour that has the greatest sensory effect at the lowest concentration is essential,” said Fisher and Philips. They suggest this be done by sensory tests, ideally using trained individuals.
They also noted that the exact mechanism for citrus essential oils’ antimicrobial properties is not known, although there are several good theories. These include morphological changes – and indeed some studies have indicated that essential oils could cause the outer membrane of some bacteria to disintegrate; while others have noted major thickening and disruption of the cell wall.