Spices and herbs have been used for thousands of centuries by many cultures to enhance the flavor and aroma of foods. Early cultures also recognized the value of using spices and herbs in preserving foods and for their medicinal value. Scientific experiments since the late 19th century have documented the antimicrobial properties of some spices, herbs, and their components (17, 20).

Antimicrobial Effectiveness of Spices and Herbs
Table 1 describes the relative antimicrobial effectiveness of some spices and herbs.

Table 1. Antimicrobial Effectiveness of Spices and Herbs*

Spices and Herbs
Inhibitory Effect
Cinnamon, cloves, mustard Strong
Allspice, bay leaf, caraway, coriander, cumin, oregano, rosemary, sage, thyme Medium
Black pepper, red pepper, ginger Weak

 * Adapted from Zaika (20).
Studies in the past decade confirm that the growth of both gram-positive and gram-negative foodborne bacteria, yeast. and mold can be inhibited by garlic, onion, cinnamon, cloves, thyme, sage, and other spices. Effects of the presence of these spices / herbs can be seen in food products such as pickles, bread, rice, and meat products. The fat, protein, water, and salt contents of food influence microbial resistance. Thus, it is observed that higher levels of spices are necessary to inhibit growth in food than in culture media (17). Table 2 is a list of various spices and herbs and their inhibitory effect on various microorganisms.

Table 2. Inhibitory Effects of Spices and Herbs*

Spice / Herb 
Garlic Salmonella typhymurium, Escherichia coli, Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, mycotoxigenic Aspergillus, Candida albicans (1, 5, 9, 15)
Onion Aspergillus flavis, Aspergillus parasiticus (16)
Cinnamon Mycotoxigenic Aspergillus, Aspergillus parasiticus (1, 3, 4)
Cloves Mycotoxigenic Aspergillus (1, 7)
Mustard Mycotoxigenic Aspergillus (1)
Allspice Mycotoxigenic Aspergillus (1, 7)
Oregano Mycotoxigenic Aspergillus, Salmonella spp., Vibrio parahaemolyticus (1, 2, 10, 12)
Rosemary Bacillus cereus, Staphylococcus aureus, Vibrio parahaemolyticus (19)
Bay leaf Clostridium botulinum  (8)
Sage Bacillus cereus, Staphylococcus aureus, Vibrio parahaemolyticus  (18, 19)
Thyme Vibrio parahaemolyticus (2, 12)

* Adapted from Shelef (17).
Microbial Contamination of Spices
Spices and herbs may be contaminated because of conditions in which they were grown and harvested. Spores of both Clostridium perfringens and Bacillus cereus have been found to be present in spices and herbs (11, 13). Contaminated spices have been reported to have been causes of foodborne illness and spoilage. Fewer microorganisms are present in spices with higher antimicrobial activity such as sage, cloves, and oregano. However, all spices and herbs should be cleaned and decontaminated with ethylene oxide, irradiation, or other acceptable methods (6).

Antimicrobial Compounds in Spices and Herbs
Essential oils extracted from spices and herbs are generally recognized as containing the active antimicrobial compounds. Table 3 is a list of the proximate essential oil content of some spices and herbs and their antimicrobial components.

Table 3. Antimicrobial Components of Spices and Herbs*

Spice / Herb 
Proximate Essential Oil Content (%)
 Antimicrobial Component(s) 
0.3 – 0.5 
0.5 – 1.0 
Allyl isothiocyanate
0.5 – 2.0 
Cinnamaldehyde, Eugenol
16 – 18
0.7 – 2.0 
Thymol, Eugenol
0.8 – 0.9
Thymol, Carvacrol

* Adapted from Shelef (17).
Allicin and allyl isothocyanate are sulfur-containing compounds. Allicin, isolated from garlic oil, inhibits the growth of both gram-negative and gram-positive bacteria. Sulfur-containing compounds are also present in onions, leeks, and chives.

Eugenol, carvacrol, and thymol are phenol compounds and, as Table 3 indicates, are found in cinnamon, cloves, sage, and oregano. The essential oil fraction is particularly high in cloves, and eugenol comprises 95% of the fraction. The presence of these compounds in cinnamon and cloves, when added to bakery items, function as mold inhibitors in addition to adding flavor and aroma to baked products. Paster et al. (14) have shown that essential oils of oregano and thyme (which contain carvacrol and thymol) are effective as fumigants against fungi on stored grain. These investigators have proposed using them as an alternative to chemicals for preseving stored grains.
Antioxidant Action
Spice extractives, such as oleoresin of rosemary, can provide inhibition of oxidative rancidity and retard the development of “warmed-over” flavor in some products. Thus, some spices not only provide flavor and aroma to food and retard microbial growth, but are also beneficial in prevention of some off-flavor development. These attributes are useful in the development of snack foods and meat products (6).

Although the antimicrobial activity of some spices and herbs is documented, the normal amounts added to foods for flavor is not sufficient to completely inhibit microbial growth. The antimicrobial activity varies widely, depending on the type of spice or herb, test medium, and microorganism. For these reasons, spice antimicrobials should not be considered as a primary preservative method (6). However, the addition of herbs and spices can be expected to aid in preserving foods held at refrigeration temperatures, at which the multiplication of microorganisms is slow.

Zaika (20) has given an excellent summary of the antimicrobial effectiveness of spices and herbs. A partial listing of this summary is as follows.

  1. Microorganisms differ in their resistance to a given spice or herb.
  2. A given microorganism differs in its resistance to various spices and herbs.
  3. Bacteria are more resistant than fungi.
  4. The effect on spores may be different than that on vegetative cells.
  5. Gram-negative bacteria are more resistant than gram-positive bacteria.
  6. The effect of a spice or herb may be inhibitory or germicidal.
  7. Spices and herbs harbor microbial contaminants.
  8. Spices and herbs may serve as substrates for microbial growth and toxin production.
  9. Amounts of spices and herbs added to foods are generally too low to prevent spoilage by microorganisms.
  10. Active components of spices / herbs at low concentrations may interact synergistically with other factors (NaCl, acids, preservatives) to increase preservative effect.
  11. Nutrients present in spices / herbs may stimulate growth and/or biochemical activities of microorganisms.

Thus, food product safety and shelf life depend in some part on the type, quantity, and character of spices and herbs added to the products.