Natural antimicrobials as additives and ingredients for the preservation of foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 141

et al. 1987; Kamal and Motohiro 1986; Uyttendaele and Debevere 1994;
Johansen et al. 1997) and is used as a preservative in starch-based foods in Japan
(Ueno et al. 1989). The mode of action of protamine is believed to be the
electrostatic attraction between the positively charged protamine and the
negatively charged outer cell envelope, resulting in either cell inhibition or death
due to leakage of essential cellular material (Islam et al. 1987; Johanssen et al.
1997; Stumpe and Bakker 1997).

6.4 Natural antimicrobials derived from plants
Plants protect themselves against microorganisms and other predators by
synthesising a wide range of compounds. Such compounds include essential oils,
phytoalexins, phenolics and related compounds. Herbs and spices are often rich in
such compounds. It is recognised that such compounds can be cidal, sporostatic or
sporicidal in respect to bacterial spores, as well as inhibitors of mycotoxin
production (Beuchat 1994; Nychas 1995; Davidson and Naidu 2000). A wide
variety of spices and herbs possess antimicrobial activity (Table 6.4). There are a
number of excellent reviews on the use of antimicrobials by plants (see Section
6.9 Sources of further information and advice).
Antimicrobial compounds derived from plants can be classed as follows
(Meyer et al. 2002):

1. Pre-infectional agents at the plant surface (constitutive).
2. Agents present in vacuoles and associated with enzyme activation (constitutive).
3. Phtoalexins, which are compounds produced in response to invasion.

Usually to achieve microbial inhibition, signifi cant levels of addition of the
particular spice or herb will be required. As such products usually exhibit strong
fl avours, their application to date has largely been confi ned to foods in which the
specifi c taste, fl avour or aroma is appreciated or not noticed. Purifi ed compounds
are more active, but their application would not be approved unless extensive

￿ ￿ ￿ ￿ ￿

Table 6.4 Plants used as spices and herbs which contain compounds containing
antimicrobial activity

Allspice Coffee Lime Peppermint

Almond Coriander Mandarin Pimento

Anise Dill Marjoram Rosemary

Basil Fennel Mustard Sage

Bay Garlic Nutmeg Tarragon

Caraway Ginger Onion Tea

Cardamon Hops Orange Thyme

Celery Horseradish Paprika Turmeric

Clove Leek Parsley Vanillin

Cocoa Lemon

Source: Beuchat (1994), Roller and Board (2003).