Abstract
This work investigates the phenolic, antioxidant capacity of crude extracts of eight Egyptian medicinal plants (Syrian oregano, marjoram, rosemary, lemongrass, thyme, yarrow, marigold and sweet wormwood) and estimates their activity against Listeria monocytogenes, one of the most virulent food borne pathogens. Antioxidant activity of Rosemary (70.6±1.65%) and thyme (70.8±1.72%) based on TBA assay was significantly higher compared to other plants and ascorbic acid. Rosemary was found to possess the best antilisterial activity with lowest MBC (8 µl/ml); while its total phenolic content (TPC) represented 69.73 ± 0.47 mg/g GAE. Thyme showed MBC of 46 µl/ml with TPC 96.85±0.56 mg/g GAE. Lemon grass and marigold showed considerable antilisterial activity (MBC 31, 46 µl/ml respectively), although they had lower phenolic contents and low thiobarbituric acid inhibition. Sweet wormwood, marjoram and yarrow were inactive against listeria. Rosemary and thyme appeared as possible alternatives for synthetic food additives and preservatives. Key words: Medicinal plants, anti-listerial, antioxidant, rosemary, thyme.
Highlights
Listeria monocytogenes is the causative agent of listeriosis
The aim of this study was to (i) determine the phenolic content of the crude extract of eight medicinal plants widely cultivated in Egypt [oregano (Origanum syriacum), marjoram (Majorana hortensis), rosemary (Rosmarinus officinalis), lemongrass (Cymbopogon citratus), thyme (Thymus vulgaris), yarrow (Achillea millefolium) and sweet wormwood (Artemisia annua)]; (ii) to determine the antioxidant activity of the Egyptian crude extracts using two different antioxidant tests; and (iii) to determine their effectiveness against L. monocytogenes
The total phenolic content (TPC) varied from 22.08±0.32 to where thyme showed the highest content (96.85 ± 0.56 mg/g gallic acid equivalent (GAE)) > Syrian oregano > rosemary and marjoram > Yarrow > sweet wormwood > lemongrass
Summary
Listeria monocytogenes is the causative agent of listeriosis. In the 1980s, a number of outbreaks of listeriosis occurred, in which contaminated foods were identified to be the source of transmission. Poultry, seafood products, fruits and vegetable products have been involved in Listeria monocytogenes outbreaks (Schlech and Acheson, 2000). L. monocytogenes is one of the most virulent food borne pathogens, with 20 to 30% of clinical infections resulting in death (Ramaswamy et al, 2007); its fatality rates even exceed that caused by Salmonella and Clostridium botulinum (Dharmarha, 2008). It is resistant to different environmental conditions, including acid pH, high NaCl concentration, and refrigeration temperatures. It can grow in many foods when stored at refrigeration temperatures (Embarek and Huss, 1993)
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