http://naturalingredient.org/wp/wp-content/uploads/Burt_Essential_Oils_A_Review_2004.pdf

Essential oils: their antibacterial properties and potential applications in foods--a review.

Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds’ mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.

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Essential oils in food preservation: mode of action, synergies, and interactions with food matrix components.

While use of synthetic antioxidants (such as butylated hydroxytoluene and butylated hydroxyanisole) to maintain the quality of ready-to-eat food products has become commonplace, consumer concern regarding their safety has motivated the food industry to seek natural alternatives. Phenolic antioxidants can inhibit free radical formation and/or interrupt propagation of autoxidation. Fat-soluble vitamin E (α-tocopherol) and water-soluble vitamin C (L-ascorbic acid) are both effective in the appropriate matrix. Plant extracts, generally used for their flavoring characteristics, often have strong H-donating activity thus making them extremely effective antioxidants. This antioxidant activity is most often due to phenolic acids (gallic, protocatechuic, caffeic, and rosmarinic acids), phenolic diterpenes (carnosol, carnosic acid, rosmanol, and rosmadial), flavonoids (quercetin, catechin, naringenin, and kaempferol), and volatile oils (eugenol, carvacrol, thymol, and menthol). Some plant pigments (anthocyanin and anthocyanidin) can chelate metals and donate H to oxygen radicals thus slowing oxidation via 2 mechanisms. Tea and extracts of grape seeds and skins contain catechins, epicatechins, phenolic acids, proanthocyanidins, and resveratrol, all of which contribute to their antioxidative activity. The objective of this article is to provide an overview of natural antioxidants, their mechanisms of action, and potential applications.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1541-4337.2011.00156.x

Natural antioxidants: sources, compounds, mechanisms of action, and potential applications

Total equivalent antioxidant capacity (TEAC) and phenolic content of 26 common spice extracts from 12 botanical families were investigated. Qualitative and quantitative analyses of major phenolics in the spice extracts were systematically conducted by reversed-phase high-performance liquid chromatography (RP-HPLC). Many spices contained high levels of phenolics and demonstrated high antioxidant capacity. Wide variation in TEAC values (0.55−168.7 mmol/100 g) and total phenolic content (0.04−14.38 g of gallic acid equivalent/100 g) was observed. A highly positive linear relationship (R2 = 0.95) obtained between TEAC values and total phenolic content showed that phenolic compounds in the tested spices contributed significantly to their antioxidant capacity. Major types of phenolic constituents identified in the spice extracts were phenolic acids, phenolic diterpenes, flavonoids, and volatile oils (e.g., aromatic compounds). Rosmarinic acid was the dominant phenolic compound in the six spices of the family La...

Antioxidant Capacity of 26 Spice Extracts and Characterization of Their Phenolic Constituents

The increasing resistance of microorganisms to conventional chemicals and drugs is a serious and evident worldwide problem that has prompted research into the identification of new biocides with broad activity. Plants and their derivatives, such as essential oils, are often used in folk medicine. In nature, essential oils play an important role in the protection of plants. Essential oils contain a wide variety of secondary metabolites that are capable of inhibiting or slowing the growth of bacteria, yeasts and moulds. Essential oils and their components have activity against a variety of targets, particularly the membrane and cytoplasm, and in some cases, they completely change the morphology of the cells. This brief review describes the activity of essential oils against pathogenic bacteria.

/pdf/effect-of-essential-oils-on-pathogenic-bacteria-16hlitkebz.pdf

Effect of Essential Oils on Pathogenic Bacteria

The volatile oils of black pepper [Piper nigrum L. (Piperaceae)], clove [Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae)], geranium [Pelargonium graveolens L'Herit (Geraniaceae)], nutmeg [Myristica fragrans Houtt. (Myristicaceae), oregano [Origanum vulgare ssp. hirtum (Link) Letsw. (Lamiaceae)] and thyme [Thymus vulgaris L. (Lamiaceae)] were assessed for antibacterial activity against 25 different genera of bacteria. These included animal and plant pathogens, food poisoning and spoilage bacteria. The volatile oils exhibited considerable inhibitory effects against all the organisms under test while their major components demonstrated various degrees of growth inhibition.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2000.00969.x

Antimicrobial agents from plants: antibacterial activity of plant volatile oils.

Five essential oils, geranium, monarda, nutmeg, oregano and thyme, were evaluated for their antioxidant properties at final concentrations of 0.75 ppm to 100 ppm. Thiobarbituric acid reactive substances (TBARS) were measured in three avian assay systems based on egg yolk, one-day old chicken livers and muscle from mature chickens. All the oils demonstrated extensive antioxidant capacities. The egg yolk TBARS assay showed monarda, nutmeg and thyme essential oils to be the most effective while the chick liver assay revealed nutmeg oil to be the most active. The chicken muscle assay demonstrated equal activity for the oils of monarda, nutmeg, oregano and thyme. Based on this assay technique, oils demonstrating the most effective antioxidant capacities will be chosen for feeding trials to demonstrate their effectiveness in vivo upon polyunsaturated fatty acid (PUFA) metabolism during vital periods of the lifespan, in particular, the foetal/neonate and aging periods.

Evaluation in vitro of plant essential oils as natural antioxidants

The antioxidant capacity of the synthetic antioxidants BHA, BHT, pyrogallol and α-tocopherol, the essential oils from black pepper, clove, geranium, melissa, nutmeg, oregano and thyme and 33 phytoconstituents were assessed in vitro, using an antioxidant assay. All die compounds demonstrated antioxidant capacity superior to the water soluble α-tocopherol analogue Trolox with the exception of the essential oil melissa and the phytoconstituents aromadendrene, myrcene and nerol. Clove, oregano and thyme were exceptionally potent in this assay, comparable with the activities of both BHA and pyrogallol. Eugenol, carvacrol, and thymol similarly demonstrated an equivalent degree of activity. These phytoconstituents are the major components present in clove, oregano and thyme essential oils, respectively.

H. J. D. Dorman

Papers

Antimicrobial agents from plants: antibacterial activity of plant volatile oils.

Evaluation in vitro of plant essential oils as natural antioxidants

In vitro antioxidant activity of a number of plant essential oils and phytoconstituents.