The tide is currently turning against chemical-based anti-fungal additives 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.
"It seems that citrus essential oils could be considered suitable alternatives to chemical additives for use in the food industry, attending to the needs for safety and satisfying the demand of consumers for natural components," wrote the researchers from Miguel Hernandez University in Alicante.
The study, published in the journal Food Chemistry , reports that essential oils of lemon, mandarin, grapefruit and orange all exhibited antifungal activity against the common food moulds Aspergillus niger, Aspergillus flavus, Penicillium chrysogenum and Penicillium verrucosum .
According to the researchers, essential oil from orange was the most effective against A. niger (50 per cent reduction).
The mandarin produced the best effects against A. flavus (65 per cent reduction), and grapefruit came out on top against P. chrysogenum and P. verrucosum (48.1 and 48.3 per cent, respectively).
The protective effects against growth were proposed to be due to toxic effects of the essential oil on the functionality and structure of the cell membrane in the mould.
The researchers also note that other studies have indicated that inhibition may also be due to the monoterpenes content of essential oils .
"These components would increase the concentration of lipidic peroxides such as hydroxyl, alkoxyl and alkoperoxyl radicals and so bring about cell death," they said.
Potential for essential oils "The main advantage of essential oils is that they can be used in any foods and are considered generally recognized as safe (GRAS), as long as their maximum effects is attained with the minimum change in the organoleptic properties of the food," wrote the Alicante-based researchers.
Indeed, the search for natural alternatives to synthetic additives has increased the attention on essential oils.
Katie Fisher and Carol Philips of the University of Nottingham's School of Health, UK, reviewed the potential of essential oils as inhibitors of both gram-positive and gram-negative bacteria.
The review, published in Trends in Food Science and Technology , noted that the antimicrobial properties of citrus essential oils have only started to be explored quite recently.
Fisher and Philips sounded a note of caution, however: "Should essential oils 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 essential oils 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.
Source: Food Chemistry Published online ahead of print, doi: 10.1016/j.foodcont.2007.12.003 "Antifungal activity of lemon ( Citrus lemon L.), mandarin ( Citrus reticulata L.), grapefruit ( Citrus paradisi L.) and orange ( Citrus sinensis L.) essential oils" Authors: M. Viuda-Martos, Y. Ruiz-Navajas, J. Fernandez-Lopez, J. Perez-Alvarez