Food safety is regarded to be an important public health issue in the present world (WHO, 2002). High incidence of food borne diseases and diarrhoeal diseases worldwide provoked the researchers to couple new methods to eliminate food pathogens in combination with the existing methods (the hurdle principle, Leistner, 1978). WHO has recently called for worldwide reduction in the consumption of common salt due to the increasing risk of cardiovascular disease (WHO, 2002). So the scope of new methods for food safety arouse with a natural or ‘green’ image. One of the possibilities is to use Essential oil as antibacterial additives. Essential oils are aromatic oily liquids obtained from plant material (flower, bud, seed, leaves, twigs, bark, herbs, wood, fruits and roots). The term ‘Essential oil’ (EO) was thought to be coined by Paracelsus Von Hohenheim, who named the effective component of a drug ‘Quinta Essentia’ (Guenther, 1948). Besides antibacterial property EOs are proven to have antiviral, antimycotic, antioxidant, antiparasitic and insecticidal properties.
Essential oils (volatile or ethereal oils) are complex mixtures of volatile compounds produced by living organisms and isolated by physical means only (pressing and distillation) from a whole plant or plant part of known taxonomic origin. An estimated 3000 essential oils are known, many are used for fragrance and flavours. Essential oils can comprise more than 60 individual components. The composition of essential oils in a particular species of plant differs between seasons and geographical sources. Generally, oils produced from herbs extracted during or immediately after flowering possess strong antimicrobial activity. The strength of antibacterial activity is determined by the dilution of Essential oil in agar or broth. In broth dilution studies a number of different techniques determine end point- Optical density measurement and enumeration of colony via. viable count. Disc diffusion and agar wells are used to screen antibacterial activity. The physical effects of antibacterial activity were studied using Scanning Electron Microscopy (SEM).
The hydrophobicity of essential oils enables them to partition the lipid layer of bacterial cell membrane and mitochondrion, disturbing structures more permeable. This will lead to leakage of ions and other cell contents, when exceeds a limit lead to lysis and death. The mechanism affects disturbance to cytoplasmic membrane disrupting Proton Motive Force (PMF), electron flow, active transport and coagulation of cell contents. Two possible mechanisms exist whereby cyclic hydrocarbons act on lipid molecules on cytoplasmic membrane. Lipophilic hydrocarbon molecules accumulate in lipid bilayer and distort lipid-protein interaction. Alternatively direct interaction is also possible. Some EOs act to stimulate the growth of pseudomycelia on yeast, indicating that EOs act on enzymes involved in energy regulation or synthesis of structural components. The phenolic components are responsible for the antibacterial properties of essential oils (Cosentinoet al., 1999).
Based on the data available on EO in foods the order of antimicrobial agents in the decreasing order is as Oregano/Clove/Coriander/Cinnamon, Thyme, Mint, Rosemary, Mustard and Cilantro/Sage where as EO components are as Eugenol, Carvacrol/Cinnamic acid, Cinnamaldehyde and Geraniol.
Eugenol, coriander, clove, oregano and thyme oils at the rate of 5-20 µlg-1 were found to be effective against Listeria monocytogenes, Aeromonashydrophila and spoilage flora in meat products causing marked reduction in the initial number of recoverable cells while mint and sage oils are less effective. Oregano oil is widely used in packed meat and well-studied against Clostridium botulinum spores upto 0.4µlg-1. Mint oil at the rate of 5-20µlg-1 is found effective against Salmonella Enteritidis in low fat yoghurt and inhibition of the starter culture at 0.05-5.0µlg-1, but cinnamon, cardamom and clove oils are effective. Oregano oil at the rate of 7-21µlg-1is effective against E coli O157:H7.
Products without preservatives, free from microbial growth, toxins and other quality deteriorating factors maintaining freshness and sensorial qualities is a challenge from part of consumers for packaging. Due to the rise of green consumerism (Smid and Goris, 1999) which stimulates use and development of herbal products, essential oils gain more attraction to cosmetics, food industry and medical sector. Bioengineering of the synthesis of essential oils in plants give better yield and open up a new future. The incorporation of essential oils on to the active packaged products will be surely acceptable by the consumers owing to their natural antimicrobial action which would be a cutting edge technology for future.