A Comparative Study of Antimicrobial and Antioxidant Activities of Plant Essential Oils and Extracts as Candidate Ingredients for Edible Coatings to Control Decay in ‘Wonderful’ Pomegranate

Abstract

This study determined the antimicrobial and antioxidant activity of lemongrass (LO), thyme (TO), and oregano (OO) essential oils and ethanolic extracts of pomegranate peel (PPE) and grape pomace (GPE) as candidate ingredients for edible coatings. Antifungal effects against Botrytis cinerea and Penicillium spp. were tested using paper disc and well diffusion methods. Radical scavenging activity (RSA) was evaluated using 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid assays. Gas chromatography-mass spectrometry analysis identified limonene (16.59%), α-citral (27.45%), β-citral (27.43%), thymol (33.31%), paracymene (43.26%), 1,8-cineole (17.53%), and trans-caryphellene (60.84%) as major compounds of the essential oils. From both paper disc and well diffusion methods, LO recorded the widest zone of inhibition against tested microbes (B. cinerea and Penicillium spp.). The minimum inhibitory concentrations of LO against B. cinerea and Penicillium spp., were 15 µL/mL and 30 µL/mL, respectively. The highest (69.95%) and lowest (1.64%) RSA at 1 mg/mL were recorded for PPE and OO. Application of sodium alginate and chitosan-based coatings formulated with LO (15 or 30 µL/mL) completely inhibited spore germination and reduced the decay severity of ‘Wonderful’ pomegranate. Lemongrass oil proved to be a potential antifungal agent for edible coatings developed to extend shelf life of ‘Wonderful’ pomegranate.

Effects of Gum Arabic Coatings Enriched with Lemongrass Essential Oil and Pomegranate Peel Extract on Quality Maintenance of Pomegranate Whole Fruit and Arils

“…The resistance to decay incidence and internal decay exhibited by ‘Wonderful’ pomegranates coated with GA + LM and GA + PP corroborates with recent studies which have proven the antimicrobial activities against postharvest pathogens of either LM or PP alone and when combined with coatings [ 60 , 96 ]. In this present study, internal decay observed was due to grey mold ( Botrytis cinerea ) and blue mold ( Penicillium spp.)…”

“…Studies have shown that the application of edible coatings on pomegranate fruit stored under low temperature conditions suppressed decay weight loss and maintained overall quality [ 58 , 59 ]. Similarly, Kawhena et al [ 60 , 61 ] demonstrated the efficacy gum arabic, sodium alginate and starch-based coatings to minimize weight loss and decay severity in ‘Wonderful’ pomegranates during cold storage and shelf life. However, to the best of our knowledge, few reports exist which show the effect of coatings enriched with active components such PP and/or LM on postharvest quality of any pomegranate fruit during storage and shelf life.…”

Antifungal Activities and Mode of Action of Cymbopogon citratus, Thymus vulgraris, and Origanum heracleoticum Essential Oil Vapors against Botrytis cinerea and Their Potential Application to Control Postharvest Strawberry Gray Mold

“…Meanwhile, in Tv, thymol was the main component (22.71%), followed by p-cymene and γ-terpinene. Thymol is an isomer of carvacrol, with differences in the hydroxyl group position [11]. Studies have reported that the antifungal activity of thymol and carvacrol was related to the hydroxyl group position and the species of fungus.…”

“…All three compounds are monoterpenes with hydroponic and lipophilic characteristics, making it easy to attach to the membrane's hydrophobic region and dissolve in the phospholipid bilayer, leading to fungal death [8]. In carvacrol and thymol, the phenolic hydroxyl groups might have damaged the cell membrane by oxidative phosphorylation uncoupling, which contributed to the higher antifungal activities of Tv and Oh [11].…”

“…Research studies have proven that some essential oils could damage the fungal membrane and promote electrolyte leakage, resulting in fungal death. So far, some essential oils have been reported to control plant diseases caused by various fungal pathogens, such as Botrytis, Rhizopus, Penicillium, Alternaria, and Monilinia, on fresh fruits and vegetables [9][10][11]. However, essential oils to prevent plant disease in the fields are limited due to their volatile characteristics.…”