Herbs and spices are used widely in the food industry as flavours and fragrances. However, they also exhibit useful antimicrobial and antioxidant properties. Many plant-derived antimicrobial compounds have a wide spectrum of activity against bacteria, fungi and mycobacteria and this has led to suggestions that they could be used as natural preservatives in foods (Farag et al., 1989; Ramadan et al., 1972; Conner and Beuchat, 1984a,b; Galli et al., 1985). Although more than 1300 plants have been reported as potential sources of antimicrobial agents (Wilkins and Board, 1989), such alternative compounds have not been sufficiently exploited in foods to date.
In this post, the antimicrobial compounds from herbs and spices are reviewed and the barriers to the adoption of these substances as food preservatives are discussed. The mode of action of essential oils and the potential for development of resistance are also discussed. The focus is primarily on bacteria and fungi in prepared foods.
Barriers to the use of herb and spice essential oils as antimicrobials in foods
Since ancient times, spices and herbs have not been consciously added to foods as preservatives but mainly as seasoning additives due to their aromatic properties. Although the majority of essential oils from herbs and spices are classified as Generally Recognized As Safe (GRAS) (Kabara, 1991), their use in foods as preservatives is limited because of flavour considerations, since effective antimicrobial doses may exceed organoleptically acceptable levels. This problem could possibly be overcome if answers could be given to the following questions:
• Can the inhibitory effect of an essential oil (a mixture of many compounds) be attributed
to one or several key constituents?
• Does the essential oil provide a synergy of activity, which simple mixtures of components
cannot deliver?
• What is the minimum inhibitory concentration (MIC) of the active compound(s) of the
essential oil?
• How is the behaviour of the antimicrobial substance(s) affected by the homogeneous
(liquid, semisolid) or heterogeneous (emulsions, mixtures of solids and semisolids)
structure of foodstuffs?
• Could efficacy be enhanced by combinations with traditional (salting, heating, acidifica-
tion) and modern (vacuum packing, VP, modified atmosphere packing, MAP) methods
of food preservation?
An in-depth understanding of the antimicrobial properties of these compounds is needed to answer these questions but such understanding has been lacking, despite the burgeoning literature on the subject. Methodological limitations (discussed in more detail below) in the
evaluation of antimicrobial activity in vitro have led to many contradictory results. More-
over, there have been too few studies in real foods (these are considered laborious and often
lead to negative outcomes). There is also a need to investigate the appropriate mode of application of an essential oil in a foodstuff. For instance, immersion, mixing, encapsulation, surface-spraying, and evaporating onto active packaging are some promising methods
of adding these compounds to foods that have not been extensively investigated.
In this post, the antimicrobial compounds from herbs and spices are reviewed and the barriers to the adoption of these substances as food preservatives are discussed. The mode of action of essential oils and the potential for development of resistance are also discussed. The focus is primarily on bacteria and fungi in prepared foods.
Barriers to the use of herb and spice essential oils as antimicrobials in foods
Since ancient times, spices and herbs have not been consciously added to foods as preservatives but mainly as seasoning additives due to their aromatic properties. Although the majority of essential oils from herbs and spices are classified as Generally Recognized As Safe (GRAS) (Kabara, 1991), their use in foods as preservatives is limited because of flavour considerations, since effective antimicrobial doses may exceed organoleptically acceptable levels. This problem could possibly be overcome if answers could be given to the following questions:
• Can the inhibitory effect of an essential oil (a mixture of many compounds) be attributed
to one or several key constituents?
• Does the essential oil provide a synergy of activity, which simple mixtures of components
cannot deliver?
• What is the minimum inhibitory concentration (MIC) of the active compound(s) of the
essential oil?
• How is the behaviour of the antimicrobial substance(s) affected by the homogeneous
(liquid, semisolid) or heterogeneous (emulsions, mixtures of solids and semisolids)
structure of foodstuffs?
• Could efficacy be enhanced by combinations with traditional (salting, heating, acidifica-
tion) and modern (vacuum packing, VP, modified atmosphere packing, MAP) methods
of food preservation?
An in-depth understanding of the antimicrobial properties of these compounds is needed to answer these questions but such understanding has been lacking, despite the burgeoning literature on the subject. Methodological limitations (discussed in more detail below) in the
evaluation of antimicrobial activity in vitro have led to many contradictory results. More-
over, there have been too few studies in real foods (these are considered laborious and often
lead to negative outcomes). There is also a need to investigate the appropriate mode of application of an essential oil in a foodstuff. For instance, immersion, mixing, encapsulation, surface-spraying, and evaporating onto active packaging are some promising methods
of adding these compounds to foods that have not been extensively investigated.
