Food Protection with Chemicals, and by Biocontrol 303
alone is generally sufficient to prevent growth of bacteria in these foods but not that of certain molds
and yeasts. As used in acidic foods, benzoate acts essentially as a mold and yeast inhibitor, although
it is effective against some bacteria in the 50–500-ppm range. Against yeasts and molds at around
pH 5.0–6.0, 100–500 ppm are effective in inhibiting the former, whereas for the latter, 30–300 ppm
are inhibitory. In foods such as fruit juices, benzoates may impart disagreeable tastes at the maximum
level of 0.1%. The taste has been described as being “peppery” or burning.
The three parabens that are permissible in foods in the United States are heptyl-, methyl-, and
propylparaben; butyl- and ethylparabens are permitted in food in certain other countries. As esters of
p-hydroxybenzoic acid, they differ from benzoate in their antimicrobial activity in being less sensitive
to pH. Although not as much data have been presented on heptylparaben, it appears to be quite effective
against microorganisms, with 10–100 ppm effecting complete inhibition of some Gram-positive and
Gram-negative bacteria. Propylparaben is more effective than methylparaben on a parts per million
basis, with up to 1,000 ppm of the former and 1,000–4,000 ppm of the latter needed for bacterial
inhibition, with Gram-positive bacteria being more susceptible than Gram negatives to the parabens in
general.
38 Heptylparaben is reported to be effective against the malo-lactic bacteria. In a reduced-broth
medium, 100 ppm propylparaben delayed germination and toxin production by Clostridium botulinum
type A; and 200 ppm effected inhibition up to 120 hours at 37
◦ C.
157 In the case of methylparaben,
1,200 ppm were required for inhibition similar to that for the propyl analog.
The parabens appear to be more effective against molds than yeasts. As with bacteria, the propyl
derivative appears to be the most effective where 100 ppm or less are capable of inhibiting some yeasts
and molds, whereas for heptyl- and methylparabens, 50–200 and 500–1,000 ppm, respectively, are
required.
Like benzoic acid and its sodium salt, the methyl- and propylparabens are permissible in foods up
to 0.1%, and heptylparaben is permitted in beers to a maximum of 12 ppm and up to 20 ppm in fruit
drinks and beverages. The pK for these compounds is around 8.47, and their antimicrobial activity is
not increased to the same degree as for benzoate with the lowering of pH as noted. They have been
reported to be effective at pH values up to 8.0. For a more thorough review of these preservatives, see
reference 38.
Similarities between the modes of action of benzoic and salicylic acids have been noted.
17 Both
compounds, when taken up by respiring microbial cells, blocked the oxidation of glucose and pyruvate
at the acetate level in Proteus vulgaris. With P. vulgaris, benzoic acid caused an increase in the rate
of O 2 consumption during the first part of glucose oxidation.
17 The benzoates, like propionate and
sorbate, act against microorganisms by inhibiting the cellular uptake of substrate molecules.
62 The
stage of endospore germination most sensitive to benzoate is noted in Figure 13–1.
The undissociated form is essential to the antimicrobial activity of benzoate as well as for other
lipophilics such as sorbate and propionate. In this state, these compounds are soluble in the cell
membrane and act apparently as proton ionophores.
73 As such, they facilitate proton leakage into cells
and thereby increase energy output of cells to maintain their usual internal pH. With the disruption in
membrane activity, amino acid transport is adversely affected.
73 The mechanism of action is further
described under section “Sorbic Acid” below.
SORBIC ACID
Sorbic acid (CH 3 CH–CHCH–CHCOOH) is employed as a food preservative, usually as the calcium, sodium, or potassium salt. These compounds are permissible in foods at levels not to exceed
0.2%. Like sodium benzoate, they are more effective in acid foods than neutral foods and tend to
alone is generally sufficient to prevent growth of bacteria in these foods but not that of certain molds
and yeasts. As used in acidic foods, benzoate acts essentially as a mold and yeast inhibitor, although
it is effective against some bacteria in the 50–500-ppm range. Against yeasts and molds at around
pH 5.0–6.0, 100–500 ppm are effective in inhibiting the former, whereas for the latter, 30–300 ppm
are inhibitory. In foods such as fruit juices, benzoates may impart disagreeable tastes at the maximum
level of 0.1%. The taste has been described as being “peppery” or burning.
The three parabens that are permissible in foods in the United States are heptyl-, methyl-, and
propylparaben; butyl- and ethylparabens are permitted in food in certain other countries. As esters of
p-hydroxybenzoic acid, they differ from benzoate in their antimicrobial activity in being less sensitive
to pH. Although not as much data have been presented on heptylparaben, it appears to be quite effective
against microorganisms, with 10–100 ppm effecting complete inhibition of some Gram-positive and
Gram-negative bacteria. Propylparaben is more effective than methylparaben on a parts per million
basis, with up to 1,000 ppm of the former and 1,000–4,000 ppm of the latter needed for bacterial
inhibition, with Gram-positive bacteria being more susceptible than Gram negatives to the parabens in
general.
38 Heptylparaben is reported to be effective against the malo-lactic bacteria. In a reduced-broth
medium, 100 ppm propylparaben delayed germination and toxin production by Clostridium botulinum
type A; and 200 ppm effected inhibition up to 120 hours at 37
◦ C.
157 In the case of methylparaben,
1,200 ppm were required for inhibition similar to that for the propyl analog.
The parabens appear to be more effective against molds than yeasts. As with bacteria, the propyl
derivative appears to be the most effective where 100 ppm or less are capable of inhibiting some yeasts
and molds, whereas for heptyl- and methylparabens, 50–200 and 500–1,000 ppm, respectively, are
required.
Like benzoic acid and its sodium salt, the methyl- and propylparabens are permissible in foods up
to 0.1%, and heptylparaben is permitted in beers to a maximum of 12 ppm and up to 20 ppm in fruit
drinks and beverages. The pK for these compounds is around 8.47, and their antimicrobial activity is
not increased to the same degree as for benzoate with the lowering of pH as noted. They have been
reported to be effective at pH values up to 8.0. For a more thorough review of these preservatives, see
reference 38.
Similarities between the modes of action of benzoic and salicylic acids have been noted.
17 Both
compounds, when taken up by respiring microbial cells, blocked the oxidation of glucose and pyruvate
at the acetate level in Proteus vulgaris. With P. vulgaris, benzoic acid caused an increase in the rate
of O 2 consumption during the first part of glucose oxidation.
17 The benzoates, like propionate and
sorbate, act against microorganisms by inhibiting the cellular uptake of substrate molecules.
62 The
stage of endospore germination most sensitive to benzoate is noted in Figure 13–1.
The undissociated form is essential to the antimicrobial activity of benzoate as well as for other
lipophilics such as sorbate and propionate. In this state, these compounds are soluble in the cell
membrane and act apparently as proton ionophores.
73 As such, they facilitate proton leakage into cells
and thereby increase energy output of cells to maintain their usual internal pH. With the disruption in
membrane activity, amino acid transport is adversely affected.
73 The mechanism of action is further
described under section “Sorbic Acid” below.
SORBIC ACID
Sorbic acid (CH 3 CH–CHCH–CHCOOH) is employed as a food preservative, usually as the calcium, sodium, or potassium salt. These compounds are permissible in foods at levels not to exceed
0.2%. Like sodium benzoate, they are more effective in acid foods than neutral foods and tend to