Food Protection with Chemicals, and by Biocontrol 323
pools. Another flavor compound that imparts the aroma of butter is 2,3-pentanedione, and it has been
found to be inhibitory to a limited number of Gram-positive bacteria and fungi at 500 ppm or less.
95,97
The agent l-carvone imparts spearmintlike aromas and the agent d-carvone imparts carawaylike
aromas, and both are antimicrobial, with the l-isomer being more effective than the d-isomer; both
are more effective against fungi than bacteria at 1,000 ppm or less.
97 Phenylacetaldehyde imparts a
hyacinthlike aroma and has been shown to be inhibitory to S. aureus at 100 ppm; and Candida albicans
at 500 ppm.
97,132 Menthol, which imparts a peppermintlike aroma, was found to inhibit S. aureus at
32 ppm, and E. coli and C. albicans at 500 ppm.
97,132 Vanillin and ethyl vanillin are inhibitory,
especially to fungi at levels <1,000 ppm.
Spices and Essential Oils
Although used primarily as flavoring and seasoning agents in foods, many spices possess significant
antimicrobial activity. In all instances, antimicrobial activity is due to specific chemicals or essential
oils (some are noted in Chapter 3). The search for nitrite-sparing agents generated new interest in
spices and spice extracts in the late 1970s.
179
It would be difficult to predict what antimicrobial effects, if any, are derived from spices as they are
used in foods; the quantities employed differ widely depending on taste, and the relative effectiveness
varies depending on product composition. Because of the varying concentrations of the antimicrobial
constituents in different spices and because many studies have been conducted employing them on a
dry weight basis, it is difficult to ascertain the MIC of given spices against specific organisms. Another
reason for conflicting results by different investigators is the assay method employed. In general, higher
MIC values are obtained when highly volatile compounds are evaluated on the surface of plating media
than when they are tested in pour plates or broth. When eugenol was evaluated by surface plating onto
plate count agar (PCA) at pH 6, only 9 of 14 Gram-negative and 12 of 20 Gram-positive bacteria
(including 8 lactics) were inhibited by 493 ppm, whereas in nutrient broth at the same pH, MICs of
32 and 63 were obtained for Torulopsis candida and Aspergillus niger, and S. aureus and Escherichia
coli, respectively.
95 Spice extracts are less inhibitory in media than spices, probably due to a slower
release of volatiles by the latter.
181 In spite of the difficulties of comparing results from study to study,
the antimicrobial activity of spices is unquestioned, and a large number of investigators have shown the
effectiveness of at least 20 spices or their extracts against most food-poisoning organisms, including
mycotoxigenic fungi.
179
In general, spices are less effective in foods than in culture media, and Gram-positive bacteria
are more sensitive than Gram negatives, with the lactic acid bacteria being the most resistant among
Gram positives.
221 Although results concerning them are debatable, the fungi appear in general to
be more sensitive than Gram-negative bacteria. Some Gram negatives, however, are highly sensitive.
Antimicrobial substances vary in content from the allicin of garlic (with a range of 0.3–0.5%) to
eugenol in cloves (16–18%).
179 When whole spices are employed, MIC values range from 1% to 5%
for sensitive organisms. Sage and rosemary are among the most antimicrobial as reported by various
researchers, and it has been reported that 0.3% in culture media inhibited 21 of 24 Gram-positive
bacteria and were more effective than allspice.
181 White mustard essential oil has been found to be
effective in a number of foods at levels of ca. 25–100 ppm against Gram-negative and Gram-positive
bacteria as well as against some yeasts.
With respect to specific inhibitory levels of extracts and essential oils, Huhtanen
87 made ethanol
extracts of 33 spices, tested them in broth against C. botulinum, and found that achiote and mace extracts
produced an MIC of 31 ppm and were the most effective of the 33. Next most effective were nutmeg,
bay leaf, and white and black peppers, with MICs of 125 ppm. Employing the essential oils of oregano,
pools. Another flavor compound that imparts the aroma of butter is 2,3-pentanedione, and it has been
found to be inhibitory to a limited number of Gram-positive bacteria and fungi at 500 ppm or less.
95,97
The agent l-carvone imparts spearmintlike aromas and the agent d-carvone imparts carawaylike
aromas, and both are antimicrobial, with the l-isomer being more effective than the d-isomer; both
are more effective against fungi than bacteria at 1,000 ppm or less.
97 Phenylacetaldehyde imparts a
hyacinthlike aroma and has been shown to be inhibitory to S. aureus at 100 ppm; and Candida albicans
at 500 ppm.
97,132 Menthol, which imparts a peppermintlike aroma, was found to inhibit S. aureus at
32 ppm, and E. coli and C. albicans at 500 ppm.
97,132 Vanillin and ethyl vanillin are inhibitory,
especially to fungi at levels <1,000 ppm.
Spices and Essential Oils
Although used primarily as flavoring and seasoning agents in foods, many spices possess significant
antimicrobial activity. In all instances, antimicrobial activity is due to specific chemicals or essential
oils (some are noted in Chapter 3). The search for nitrite-sparing agents generated new interest in
spices and spice extracts in the late 1970s.
179
It would be difficult to predict what antimicrobial effects, if any, are derived from spices as they are
used in foods; the quantities employed differ widely depending on taste, and the relative effectiveness
varies depending on product composition. Because of the varying concentrations of the antimicrobial
constituents in different spices and because many studies have been conducted employing them on a
dry weight basis, it is difficult to ascertain the MIC of given spices against specific organisms. Another
reason for conflicting results by different investigators is the assay method employed. In general, higher
MIC values are obtained when highly volatile compounds are evaluated on the surface of plating media
than when they are tested in pour plates or broth. When eugenol was evaluated by surface plating onto
plate count agar (PCA) at pH 6, only 9 of 14 Gram-negative and 12 of 20 Gram-positive bacteria
(including 8 lactics) were inhibited by 493 ppm, whereas in nutrient broth at the same pH, MICs of
32 and 63 were obtained for Torulopsis candida and Aspergillus niger, and S. aureus and Escherichia
coli, respectively.
95 Spice extracts are less inhibitory in media than spices, probably due to a slower
release of volatiles by the latter.
181 In spite of the difficulties of comparing results from study to study,
the antimicrobial activity of spices is unquestioned, and a large number of investigators have shown the
effectiveness of at least 20 spices or their extracts against most food-poisoning organisms, including
mycotoxigenic fungi.
179
In general, spices are less effective in foods than in culture media, and Gram-positive bacteria
are more sensitive than Gram negatives, with the lactic acid bacteria being the most resistant among
Gram positives.
221 Although results concerning them are debatable, the fungi appear in general to
be more sensitive than Gram-negative bacteria. Some Gram negatives, however, are highly sensitive.
Antimicrobial substances vary in content from the allicin of garlic (with a range of 0.3–0.5%) to
eugenol in cloves (16–18%).
179 When whole spices are employed, MIC values range from 1% to 5%
for sensitive organisms. Sage and rosemary are among the most antimicrobial as reported by various
researchers, and it has been reported that 0.3% in culture media inhibited 21 of 24 Gram-positive
bacteria and were more effective than allspice.
181 White mustard essential oil has been found to be
effective in a number of foods at levels of ca. 25–100 ppm against Gram-negative and Gram-positive
bacteria as well as against some yeasts.
With respect to specific inhibitory levels of extracts and essential oils, Huhtanen
87 made ethanol
extracts of 33 spices, tested them in broth against C. botulinum, and found that achiote and mace extracts
produced an MIC of 31 ppm and were the most effective of the 33. Next most effective were nutmeg,
bay leaf, and white and black peppers, with MICs of 125 ppm. Employing the essential oils of oregano,