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Accueil du site → Doctorat → États-Unis → 2016 → Postharvest Quality of Lettuce, Muskmelon, and Tomato after Application of Essential Oils as Innovative Disinfectants

North Carolina State University (2016)

Postharvest Quality of Lettuce, Muskmelon, and Tomato after Application of Essential Oils as Innovative Disinfectants

Jiang, Chen

Titre : Postharvest Quality of Lettuce, Muskmelon, and Tomato after Application of Essential Oils as Innovative Disinfectants

Auteur : Jiang, Chen

Université de soutenance : North Carolina State University

Grade : Doctor of Philosophy (PhD) 2016

Résumé
Foodborne illness outbreaks from fresh produce contaminated with pathogens like Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica have caused increasing concerns. Essential oils (EOs) have been evaluated at the microbial level as potential disinfectant alternatives to chlorine to maintain food safety. However, EO effects on produce quality have not been well documented. Here, experiments were performed on lettuce, tomato, and muskmelon to understand their postharvest weight loss, color, firmness, defect, and composition in response to three types of EOs (thyme, cinnamon leaf, and clove bud oils). Individual romaine lettuce (Lactuca sativa var longifolia) leaves, either storepurchased or field-harvested, were dipped in the three EOs emulsified at 0.05, 0.1, 0.2, or 0.5% in semi-water soluble whey protein or gum arabic. Leaves treated with any of the EOs at 0.5% had more severe damage (p<0.05), than those treated with any of the EOs at lower concentrations or the controls, which included oil-free whey protein or gum arabic emulsion, deionized water, 200 µl/l chlorine (pH 7), and 0.5% Citrox. At lower concentrations (0.1 and 0.05%), thyme oil treated leaves had minor damage (0.8-2) while cinnamon and clove bud oil caused no damage and were not different from the controls. Rinsing 0.5% EO treated leaves with deionized water immediately after dipping reduced symptom severity but did not eliminate damage. Cut-sections (2.5 x 5.5 cm) from top half and bottom half of leaves (greenish vs whitish) were not statistically different (p>0.05) in their response to EOs. Electrolyte leakage was higher (>10%) for leaves treated with all three EOs at the 0.5% than controls. Short-term EO vapors appeared to not cause visible leaf damage, offering potential as future produce disinfectants. Tomatoes ((Solanum lycopersicum, varieties ‘Mountain Magic’, and ‘Mountain Belle’) harvested at the “breaker” to “pink” stages were dipped in a whey protein emulsion containing 0.5% of one of the three EOs, with controls of deionized water, 200 µl/l free chlorine (pH 7), and oil-free whey protein emulsion. After treatment, fruits were stored at : 1) 20ºC for 10 days ; 2) 4ºC for 7 days followed by 20ºC for 3 days ; or 3) 13ºC for 21 days. Weight loss, firmness, surface color, and surface defects were measured over time, and composition (pH, soluble solids, lycopene, and total ascorbic acid) were determined on subsamples throughout storage periods. Tomatoes treated with cinnamon or clove oil were less red as indicated by colorimeter results. Scald, pitting, and pale color was observed from ‘Mountain Belle’ fruits in three out of four harvests, but clove and cinnamon oil treatments with cold storage enhanced the damage in only one harvest. The quality of ‘Athena’ muskmelons (Cucumis melo reticulatus) was evaluated after spraying freshly harvested fruits with 0.5% of three EOs emulsified in whey protein, or with controls of deionized water, 200 µl/l free chlorine (pH 7), or oil-free whey protein emulsion. Melons stored at 4°C for 14-21 days were evaluated on 7-day intervals for weight loss, surface color, flesh firmness, surface disorder, and composition (soluble solids, pH, β- carotene, and total ascorbic acid). No difference on shelf-life and compositions were found among melons receiving different disinfectant treatments. This research indicates that application of EOs to leafy greens should not be advised due to acute toxicity, but postharvest quality of tomatoes and muskmelons are generally not different between standard chlorine and EOs disinfection. In all the experiments, produce treated with controls, including chlorine, deionized water, and oil-free emulsions (whey protein or gum arabic) were not significantly different from each other on any parameters, and leaf damage in lettuce was not found in any of these controls. The only exception was the elevated respiration rate from whey protein treated muskmelons (with or without EOs) 7-14 d after harvest comparing to those without whey protein.

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Page publiée le 2 novembre 2016, mise à jour le 9 octobre 2018