As part of a general shift towards natural and organic foods, consumers increasing prefer foods that do not contain synthetic preservatives or antimicrobial agents.
At the same time, however, salmonella is a major concern for food safety. In 2006 in the US, the infection rate was 14.8 cases per 100,000 persons. The Healthy People 2010 Initiative aims to reduce the rate to 6.8 cases per 100,000 persons.
"Novel intervention strategies to reduce or eliminate salmonella in foods are a priority for food processors and researchers," wrote the authors of the new study, to be published in the Journal of Food Science (online ahead of print).
This is opening up new challenges for manufacturers to make safe foods that meet both the natural/organic and the food safety criteria - and for food ingredient firms to offer them appropriate ingredients to this end.
The study, conducted at the Center for Food Safety-IFSE at the University of Arkansas in the US, assessed seven citrus essential oils for their antibacterial activity against 11 serotypes or strains of salmonella using disc diffusion assay.
"Essential oils from citrus offer the potential for all natural antimicrobials for use in improving the safety of organic or all natural foods," said the researchers.
The seven citrus oils were: Cold pressed Valencia orange oil terpeneless; Valencia orange oil; cold pressed orange terpenes; high purity orange terpenes; d-limonene; terpenes from orange essence; and five-fold concentrated Valencia orange oil.
Of these, orange terpenes, single-folded d-limonene, and orange essence terpenes were all seen to inhibit salmonella activity. These were taken forward to establish their minimal inhibitory concentration (MIC) against the bacteria.
The researchers found terpenes from orange essence to be the most active compound, with a MIC of between 0.125 per cent and 0.5 per cent against the salmonella.
In comparison, the orange terpenes and d-limonese had MICs of 1 per cent.
Finally, the team used mass chromatography mass spectrometry analysis to establish the components of the terpenes from orange essence. They were found to made up mostly of d-limonene (94 per cent), and myrcene (about 3 per cent).
"These citrus essential oils may provide help for food manufacturers to increase food safety while at the same time being acceptable to consumers who prefer natural rather than synthetic antimicrobials in their food," concluded the team.
The newly published results are in keeping with other research in the same area published this year.
For example, researchers from Miguel Hernandez University in Alicante in Spain reported in the journal Food Chemistry (online ahead of print last month) 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.
"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 involved in that study.
Journal of Food Science (Institute of Food Technologists), online ahead of print
"Orange essential oils antimicrobial activities against Salmonella spp"
Authors: CA O'Brien, PG Crandall, VI Chalova, SC Ricke
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