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Citral beats oregano as antimicrobial agent in active packaging

By Joe Whitworth , 05-Feb-2013
Last updated on 05-Feb-2013 at 11:21 GMT2013-02-05T11:21:48Z

"Four season salad” bags in PP/EVOH films with oregano essential oil (A) and citral (B) from the study

Using citral is better than oregano essential oil (OEO) as an active agent on ethylene vinyl alcohol (EVOH) coated polypropylene (PP) film at reducing microorganisms on salad, according to research.

Muriel-Galet et al combined modified atmosphere packaging (MAP) with an antimicrobial active bag consisting of PP/EVOH film with oregano essential oil or citral, aiming to extend shelf-life and reduce possible microbiological risks.

Antimicrobial tests were carried out for enterobacteria, total aerobic counts, yeasts and moulds, and lactic acid and psychrotrophic bacteria.

Researchers also studied the effect of the release of the antimicrobial agent on the sensory characteristics of the salads via consumers.

The application of the EVOH coating results in an increase in the tensile resistance of the PP films and a reduction in the elongation at break or fracture strain.

Microorganism decrease

Results showed that microorganism counts decreased at the beginning of the storage period. OEO and citral samples had reductions of 1.38 log and 2.13 log respectively against enterobacterias, about 2 log against yeasts and moulds.

Total aerobic counts reduced 1.08 log with OEO and 1.23 log with citral and the reduction of lactic acid bacteria and psychrotrophic was about 2 log.

Citral-based films appeared to be more effective than materials containing oregano essential oil in reducing spoilage flora during storage time, said the researchers.

Citral has already been used for the inhibition of yeast growth and lactic acid bacteria in fruit-based salads, added Muriel-Galet et al.

EVOH acts as a high barrier material to gases when dry but when in contact with fresh vegetables, the EVOH layer becomes humid and the barrier properties are reduced as it becomes permeable.

“Although the differences were not significant, it appears that the packages containing citral as active agent had a lower CO2 content than the other two samples, as if the citral had an effect on the reduction in the respiration rate of the salad,” said the study.

Sensory study

A group of 51 consumers of ready-to-eat fresh products evaluated the smell, visual appearance, texture and general acceptability of the samples by paired comparison tests.

The sensory studies showed that the release of the active agent resulted in a non-typical smell which led the judges to prefer the control samples, whereas after long-term storage the samples in active bags were preferred, especially the one containing citral.

“The results of the present work demonstrated that packaging of minimally processed salad in MAP bags manufactured with PP/EVOH with essential oils is an appropriate way to reach a balance between the demand for microbial safety and consumer acceptability.”

Source: Food Control, Volume 30, Issue 1, March 2013, Pages 137-143

Online, ahead of print Doi: 10.1016/j.foodcont.2012.06.032

“Evaluation of EVOH-coated PP films with oregano essential oil and citral to improve the shelf-life of packaged salad”

Authors:  Virginia Muriel-Galet, Josep P. Cerisuelo, Gracia López-Carballo, Susana Aucejo, Rafael Gavara, Pilar Hernández-Muñoz

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