Application of tea tree and clove essential oil on late development stages of Butterhead lettuce: Impact on microbiological quality

- Preharvest application of tea tree and clove essential oils did not affect sensory quality.
- Preharvest successive application of tea tree and clove improved hygienic quality of lettuce at harvest.
- Preharvest successive application of tea tree reduced microbial counts after 5 days storage.
- Preharvest successive application of clove did not improved hygienic quality during storage.

Two essential oils (tea tree and clove) were applied as preharvest sanitizers on late development stages of Butterhead lettuce and its effect during postharvest storage was analyzed. The essential oils were applied in vitro (3 MIC) and proved to be effective to inhibit native microflora of Butterhead lettuce. In vivo, the essential oils were applied in a single dose (14, 10, 7, 3 and 0 days before harvest) and in successive applications. Both essential oils showed significant reductions in mesophyllic bacteria and total coliforms when applied at harvest and in successive applications. Clove showed no significant reductions in psychrophilic, yeast and molds counts. The sensorial quality of the product was assessed by a panel of trained judges. No significant differences were found between control and treated samples. After 5 days of refrigerated storage, lettuce treated with tea tree was able to reduce microbial counts after storage (2 log) without affecting sensorial characteristics. Application of clove resulted in no significant reduction on postharvest microbial counts. These results may indicate absence of long term antimicrobial activity of clove on the native microflora of Butterhead lettuce.