Spices and Their Essential Oils

Spices are roots, bark, seeds, buds, leaves, or fruit of aromatic plants added to foods as flavoring agents. It has been known since ancient times that spices and their essential oils have varying degrees of antimicrobial activity. Cloves, cinnamon, oregano, thyme, and, to a lesser extent, sage and rosemary have the strongest antimicrobial activity among spices.

The major antimicrobial components of clove and cinnamon are eugenol (2-methoxy-4-(2-propenyl)-phenol)and cinnamic aldehyde (3-phenyl-2-propenal), respectively. Cinnamon and clove extracts or their essential oils inhibit Aeromonas hydrophila, Bacillus, Enterobacter aerogenes, lactic acid bacteria, and Staphylococcus aureus in microbiological systems and in foods (8). Bullerman (83) observed that cinnamon in raisin bread inhibited growth and aflatoxin production by Aspergillus parasiticus. Cinnamon and clove were the most effective of 16 ground herbs and spices tested at 2% w/v against nine mycotoxin-producing Aspergillus and Penicillium species (84).

The antimicrobial activity of oregano and thyme has been attributed to their essential oils which contain the terpenes carvacrol (2-methyl-5-(l-methylethyl)phenol) and thymol (5-methyl-2-(l-methylethyl)phenol), respectively. These compounds have inhibitory activity against a number of bacterial species, molds, and yeasts including Bacillus subtilis, E. coli, Lactobacillus plantarum, Pedi-ococcus cerevisiae, Pseudomonas aeruginosa, Proteus, Salmonella enteritidis, S. aureus, Vibrio parahaemolyticus, and Aspergillus parasiticus (8).

The active fraction of sage and rosemary has been suggested to be the terpene fractions of the essential oils. Rosemary contains primarily borneol (endo-l,7,7-tri-methylbicyclo[2.2.1] heptan-2-ol) along with pinene, cam-phene, camphor while sage contains thujone (4-methyl-l-(l-methylethyl)bicyclo[3.1.0]-hexan-3-one). Sage and rosemary are more active against gram-positive than gram-negative bacterial strains (85). Sensitivity of Bacillus cereus, S. aureus, and Pseudomonas to sage is greatest in microbiological medium and significantly reduced in foods (86). It is theorized that loss of activity was due to solubilization of the antimicrobial fraction in the lipid of the foods.

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is a major constituent of vanilla beans, the fruit of an orchid (Vanilla planifola, Vanilla pompona, or Vanilla tahitensis). Vanillin is most active as against molds and nonlactic Grampositive bacteria (87). Vanillin at 1500 /¿g/mL significantly inhibited strains of Aspergillus in fruit-based agars containing mango, papaya, pineapple, apple, and banana (88). The compound was least effective in banana and mango agars. This was attributed to binding of the vanillin by protein or lipid in these fruits, a phenomenon demonstrated for other antimicrobial phenolic compounds (44).

Many other spices have been tested and shown to have limited or no activity. They include allspice, anise, bay leaf, black pepper, cardamom, celery seed, chili powder, coriander, cumin, curry powder, dill, fenugreek, ginger, juniper oil, mace, marjoram, mustard, nutmeg, orris root, paprika, parsley, red pepper, sesame, spearmint, tarragon, and white pepper (89).

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