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.

Herbs, spices and their active components as natural antimicrobials in foods Effect of natural antioxidants in herbs and spices on shelf life of foods Ajowan Aniseed Asafoetida Allspice Capers and caperberries Caraway Celery Chervil Fennel and fennel seed Galangal Kaffir lime leaf Lavender Lemongrass Lovage Nigella Oregano Poppy Sesame Star anise Tarragon Tamarind Other significant herbs and spices.

Handbook of Herbs and Spices

This survey of the literature on the ecological effects of roads and traffic revealed many articles published over many years in peer reviewed journals. There has also been a growing number of reports on the ecological effects of roads produced by government authorities. Whereas few reports have been published on assessing the ecological impacts, there has been a rapidly growing number of reports on methods for mitigation. Gaps in research include the effects of heavy metal accumulation and the processes and effects resulting from habitat fragmentation. There is a need to assess the effectiveness of underpasses and tunnels and the nature and functioning of buffer zones. A literature database has been assembled and is being updated.

Ecological effects of roads and traffic: a literature review

Plant extracts for the control of bacterial growth: efficacy, stability and safety issues for food application.

Control of antibiotic biosynthesis.

In India, spices have been traditionally used since ancient times, for the preservation of food products as they have been reported to have antiseptic and disinfectant properties. In this respect, a preliminary screening for antimicrobial activities of 35 different Indian spices has been carried out. Of the spices surveyed, the results indicate that clove, cinnamon, bishop's weed, chilli, horse raddish, cumin, tamarind, black cumin, pomegranate seeds, nutmeg, garlic, onion, tejpat, celery, cambodge, have potent antimicrobial activities against the test organisms Bacillus subtilis (ATCC 6633), Escherichia coli (ATCC 10536) and Saccharomyces cerevisiae (ATCC 9763). The results also establish the traditional use of spices as food preservatives, disinfectants and antiseptics.

Antimicrobial screening of some indian spices

Star anise (Illicium verum Hook f) has been shown to possess potent antimicrobial properties. Chemical studies indicate that a major portion of this antimicrobial property is due to anethole present in the dried fruit. Studies with isolated anethole (compared with standard anethole) indicated that it is effective against bacteria, yeast and fungal strains.

Antimicrobial properties of star anise (Illicium verum Hook f).

A single novel enzyme, glyoxalase III, which catalyses the conversion of methylglyoxal into D-lactate without involvement of GSH, has been detected in and purified from Escherichia coli Of several carbonyl compounds tested, only the alpha-ketoaldehydes methylglyoxal and phenylglyoxal were found to be substrates for this enzyme Glyoxalase III is active over a wide range of pH with no sharp pH optimum In its native form it has an M(r) of 82000 +/- 2000, and it is composed of two subunits of equal M(r) Glutathione analogues, which are inhibitors of glyoxalase I, do not inhibit glyoxalase III Glyoxalase III is found to be sensitive to thiol-blocking reagents The p-hydroxymercuribenzoate-inactivated enzyme could be almost completely re-activated by dithiothreitol and other thiol-group-containing compounds, indicating the possible involvement of thiol group(s) at or near the active site of the enzyme

Glyoxalase III from Escherichia coli: a single novel enzyme for the conversion of methylglyoxal into d-lactate without reduced glutathione

Two enzymes, one NADPH-dependent and another NADH-dependent which catalyze the reduction of methylglyoxal to acetol have been isolated and substantially purified from crude extracts of Escherichia coli K12 cells. Substrate specificity and formation of acetol as the reaction product by both the enzymes, reversibility of NADH-dependent enzyme with alcohols as substrates and inhibitor study with NADPH-dependent enzyme indicate that NADPH-dependent and NADH-dependent enzymes are identical with an aldehyde reductase (EC 1.1.1.2) and alcohol dehydrogenase (EC 1.1.1.1) respectively. The Km for methylglyoxal have been determined to be 0.77 mM for NADPH-dependent and 3.8 mM for NADH-dependent enzyme. Stoichiometrically equimolar amount of acetol is formed from methylglyoxal by both NADPH- and NADH-dependent enzymes. In phosphate buffer, both the enzymes are active in the pH range of 5.8–6.6 with no sharp pH optimum. Molecular weight of both the enzymes were found to be 100,000 ± 3,000 by gel filtration on a Sephacryl S-200 column. Both NADPH- and NADH-dependent enzymes are sensitive to sulfhydryl group reagents.

Arun Baran Banerjee

Papers

Antimicrobial screening of some indian spices

Antimicrobial properties of star anise (Illicium verum Hook f).

Glyoxalase III from Escherichia coli: a single novel enzyme for the conversion of methylglyoxal into d-lactate without reduced glutathione

Reduction of methylglyoxal in Escherichia coli K12 by an aldehyde reductase and alcohol dehydrogenase

Acceleration of peroxidase and catalase activities in leaves of wild dicotyledonous plants, as an indication of automobile exhaust pollution