322 Modern Food Microbiology
microorganisms, including some viruses, mycoplasmas, and protozoa. These compounds have been
evaluated extensively as nitrite-sparing agents in processed meats and in combination with other
inhibitors, and several excellent reviews have been made.
19,63
Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and TBHQ are inhibitory to
Gram-positive and Gram-negative bacteria, as well as to yeasts and molds at concentrations ranging
from about 10–1,000 ppm, depending on substrate. In general, higher concentrations are required to
inhibit in foods than in culture media, especially in high-fat foods. BHA was about 50 times less
effective against Bacillus spp. in strained chicken than in nutrient broth.
180 BHA, BHT, TBHQ, and
propyl gallate (PG) were all less effective in ground pork than in culture media.
65 Although strains
of the same bacterial species may show wide variation in sensitivity to either of these antioxidants, it
appears that BHA and TBHQ are more inhibitory than BHT to bacteria and fungi, whereas the latter
is more viristatic. To prevent growth of C. botulinum in a prereduced medium, 50 ppm of BHA and
200 ppm of BHT were required; 200 ppm of PG were ineffective.
156 Employing 16 Gram-negative
and 8 Gram-positive bacteria in culture media, Gailani and Fung
65 found the Gram positives to be
more susceptible than Gram negatives to BHA, BHT, TBHQ, and PG, with each being more effective
in nutrient agar than in brain heart infusion (BHI) broth. In nutrient agar, the relative effectiveness was
BHA > PG > TBHQ > BHT, whereas in BHI, TBHQ > PG > BHA > BHT. Conidial germination
of four Fusarium spp. was inhibited by 200 ppm BHA or propyl paraben (PP) over the pH range 4–10,
but overall, PP was more inhibitory than BHA.
191
Foodborne pathogens such as Bacillus cereus, V. parahaemolyticus, salmonellae, and S. aureus are
effectively inhibited at concentrations <500 ppm, whereas some are sensitive to as little as 10 ppm. The
pseudomonads, especially P. aeruginosa, are among the most resistant bacteria. Three toxin-producing
penicillia were inhibited significantly in salami by BHA, TBHQ, and a combination of these two at 100
ppm, whereas BHT and PG were ineffective.
116 Combinations of BHA/sorbate and BHT/monolaurin
have been shown to be synergistic against S. aureus
19,39 and BHA/sorbate against S.typhimurium.
39
BHT/TBHQ has been shown to be synergistic against aflatoxin-producing aspergilli.
116
Flavoring Agents
Of the many agents used to impart aromas and flavors to foods, some possess definite antimicrobial
effects. In general, flavor compounds tend to be more antifungal than antibacterial. The nonlactic,
Gram-positive bacteria are the most sensitive, and the lactic acid bacteria are rather resistant. The
essential oils and spices have received the most attention by food microbiologists, and the aroma
compounds have been studied more for their use in cosmetics and soaps.
Of 21 flavoring compounds examined in one study, about half had minimal inhibitory concentrations
(MIC) of 1,000 ppm or less against either bacteria or fungi.
97 All were pH sensitive, with inhibition
increasing as pH and temperature of incubation decreased. Some of these compounds are noted in
Table 13–8.
One of the most effective flavoring agents is diacetyl, which imparts the aroma of butter.
94 It is
somewhat unique in being more effective against Gram-negative bacteria and fungi than against Grampositive bacteria. In plate count agar at pH 6.0 and incubation at 30
◦ C, all but 1 of 25 Gram-negative
bacteria and 15 of 16 yeasts and molds were inhibited by 300 ppm.
91 At pH 6.0 and incubation at 5
◦ C
in nutrient broth, <10 ppm inhibited Pseudomonas fluorescens, P. geniculata, and E. faecalis; under
the same conditions except with incubation at 30
◦ C, about 240 ppm were required to inhibit these and
other organisms.
97 It appears that diacetyl antagonizes arginine utilization by reacting with argininebinding proteins of Gram-negative bacteria. The greater resistance of Gram-positive bacteria appears
to be due to their lack of similar periplasmic binding proteins and their possession of larger amino acid
microorganisms, including some viruses, mycoplasmas, and protozoa. These compounds have been
evaluated extensively as nitrite-sparing agents in processed meats and in combination with other
inhibitors, and several excellent reviews have been made.
19,63
Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and TBHQ are inhibitory to
Gram-positive and Gram-negative bacteria, as well as to yeasts and molds at concentrations ranging
from about 10–1,000 ppm, depending on substrate. In general, higher concentrations are required to
inhibit in foods than in culture media, especially in high-fat foods. BHA was about 50 times less
effective against Bacillus spp. in strained chicken than in nutrient broth.
180 BHA, BHT, TBHQ, and
propyl gallate (PG) were all less effective in ground pork than in culture media.
65 Although strains
of the same bacterial species may show wide variation in sensitivity to either of these antioxidants, it
appears that BHA and TBHQ are more inhibitory than BHT to bacteria and fungi, whereas the latter
is more viristatic. To prevent growth of C. botulinum in a prereduced medium, 50 ppm of BHA and
200 ppm of BHT were required; 200 ppm of PG were ineffective.
156 Employing 16 Gram-negative
and 8 Gram-positive bacteria in culture media, Gailani and Fung
65 found the Gram positives to be
more susceptible than Gram negatives to BHA, BHT, TBHQ, and PG, with each being more effective
in nutrient agar than in brain heart infusion (BHI) broth. In nutrient agar, the relative effectiveness was
BHA > PG > TBHQ > BHT, whereas in BHI, TBHQ > PG > BHA > BHT. Conidial germination
of four Fusarium spp. was inhibited by 200 ppm BHA or propyl paraben (PP) over the pH range 4–10,
but overall, PP was more inhibitory than BHA.
191
Foodborne pathogens such as Bacillus cereus, V. parahaemolyticus, salmonellae, and S. aureus are
effectively inhibited at concentrations <500 ppm, whereas some are sensitive to as little as 10 ppm. The
pseudomonads, especially P. aeruginosa, are among the most resistant bacteria. Three toxin-producing
penicillia were inhibited significantly in salami by BHA, TBHQ, and a combination of these two at 100
ppm, whereas BHT and PG were ineffective.
116 Combinations of BHA/sorbate and BHT/monolaurin
have been shown to be synergistic against S. aureus
19,39 and BHA/sorbate against S.typhimurium.
39
BHT/TBHQ has been shown to be synergistic against aflatoxin-producing aspergilli.
116
Flavoring Agents
Of the many agents used to impart aromas and flavors to foods, some possess definite antimicrobial
effects. In general, flavor compounds tend to be more antifungal than antibacterial. The nonlactic,
Gram-positive bacteria are the most sensitive, and the lactic acid bacteria are rather resistant. The
essential oils and spices have received the most attention by food microbiologists, and the aroma
compounds have been studied more for their use in cosmetics and soaps.
Of 21 flavoring compounds examined in one study, about half had minimal inhibitory concentrations
(MIC) of 1,000 ppm or less against either bacteria or fungi.
97 All were pH sensitive, with inhibition
increasing as pH and temperature of incubation decreased. Some of these compounds are noted in
Table 13–8.
One of the most effective flavoring agents is diacetyl, which imparts the aroma of butter.
94 It is
somewhat unique in being more effective against Gram-negative bacteria and fungi than against Grampositive bacteria. In plate count agar at pH 6.0 and incubation at 30
◦ C, all but 1 of 25 Gram-negative
bacteria and 15 of 16 yeasts and molds were inhibited by 300 ppm.
91 At pH 6.0 and incubation at 5
◦ C
in nutrient broth, <10 ppm inhibited Pseudomonas fluorescens, P. geniculata, and E. faecalis; under
the same conditions except with incubation at 30
◦ C, about 240 ppm were required to inhibit these and
other organisms.
97 It appears that diacetyl antagonizes arginine utilization by reacting with argininebinding proteins of Gram-negative bacteria. The greater resistance of Gram-positive bacteria appears
to be due to their lack of similar periplasmic binding proteins and their possession of larger amino acid