480 ◾ Fundamental Food Microbiology
Lactic Acid
Lactic acid is used as acid or sodium and potassium salts up to 2% in carbonated drinks, salad
dressings, pickled vegetables, low-heat-processed meat products, and sauces. It is less effective
than acetic, propionic, benzoic, or sorbic acids, but more effective than citric acid. It is more
effective against bacteria but quite ineffective against yeasts and molds. It produces an inhibitory effect mainly by neutralizing the membrane proton gradient. The sodium salt of lactic acid
may also reduce A W . l(+)-lactic acid is preferred over d(–)-lactic acid as a food preservative. It has
also been recommended at a 1%–2% level to wash carcasses of food animals to reduce microbial
load. 2,6
Citric Acid
Citric acid is used at 1% (or more) in nonalcoholic drinks, jams and jellies, baking products,
cheeses, canned vegetables, and sauces. It is less effective than lactic acid against bacteria as well
as yeasts and molds. Its antibacterial effect is probably by a mechanism different than that for
lipophilic acids. The antibacterial effect is partially a result of its ability to chelate divalent cations.
However, many foods can have sufficient divalent cations to neutralize this effect.
Sorbic Acid
Sorbic acid is an unsaturated acid and used either as acid or as salts of sodium, potassium, or
calcium. It is used in nonalcoholic drinks, some alcoholic drinks, processed fruits and vegetables,
dairy desserts, confectioneries, mayonnaise, salad dressings, spreads, and mustards. The concentrations used vary from 500 to 2000 ppm (0.05%–0.2%). It is more effective against molds and
yeasts than against bacteria. Among bacteria, catalase-negative species (e.g., lactic acid bacteria)
are more resistant than catalase-positive species (e.g., aerobes, Sta. aureus, and Bacillus spp.). Also,
aerobic bacteria are more sensitive to it than anaerobic bacteria. The inhibitory concentrations of
undissociated acid are as follows: ≤0.01% (100 ppm) for Pseudomonas spp., Sta. aureus, Esc. coli,
and Serratia spp.; ~0.1% for Lactobacillus spp. and Salmonella serovars; and ≤0.02% for most
yeasts and molds, but ~1.0% for Clostridium spp.
The antimicrobial effect of sorbate is produced through its inhibitory action on the functions
of some enzymes, some from the citric acid cycle. It also interferes with synthesis of the cell wall,
protein, RNA, and DNA. Also, like other organic acids, it interferes with the membrane potential
and inhibits spore germination. 2,7
Benzoic Acid
Benzoic acid is used as an acid or sodium salt at 500–2000 ppm (0.05%–0.2%) in many lowpH products, such as nonalcoholic and alcoholic beverages, pickles, confectioneries, mayonnaise and salad dressings, mustards, and cottage cheese. It is more effective against yeasts and
molds than bacteria. The inhibitory effect is produced by both the undissociated and dissociated
acids. The inhibitory concentrations of undissociated acid are 0.01%–0.02% against bacteria
and 0.05%–0.1% against yeasts and molds. The inhibitory action is produced in several ways.
It inhibits the functions of many enzymes necessary for oxidative phosphorylation. Like other
acids, it also destroys the membrane potential. In addition, it inhibits functions of membrane
proteins. 2,8,9
Lactic Acid
Lactic acid is used as acid or sodium and potassium salts up to 2% in carbonated drinks, salad
dressings, pickled vegetables, low-heat-processed meat products, and sauces. It is less effective
than acetic, propionic, benzoic, or sorbic acids, but more effective than citric acid. It is more
effective against bacteria but quite ineffective against yeasts and molds. It produces an inhibitory effect mainly by neutralizing the membrane proton gradient. The sodium salt of lactic acid
may also reduce A W . l(+)-lactic acid is preferred over d(–)-lactic acid as a food preservative. It has
also been recommended at a 1%–2% level to wash carcasses of food animals to reduce microbial
load. 2,6
Citric Acid
Citric acid is used at 1% (or more) in nonalcoholic drinks, jams and jellies, baking products,
cheeses, canned vegetables, and sauces. It is less effective than lactic acid against bacteria as well
as yeasts and molds. Its antibacterial effect is probably by a mechanism different than that for
lipophilic acids. The antibacterial effect is partially a result of its ability to chelate divalent cations.
However, many foods can have sufficient divalent cations to neutralize this effect.
Sorbic Acid
Sorbic acid is an unsaturated acid and used either as acid or as salts of sodium, potassium, or
calcium. It is used in nonalcoholic drinks, some alcoholic drinks, processed fruits and vegetables,
dairy desserts, confectioneries, mayonnaise, salad dressings, spreads, and mustards. The concentrations used vary from 500 to 2000 ppm (0.05%–0.2%). It is more effective against molds and
yeasts than against bacteria. Among bacteria, catalase-negative species (e.g., lactic acid bacteria)
are more resistant than catalase-positive species (e.g., aerobes, Sta. aureus, and Bacillus spp.). Also,
aerobic bacteria are more sensitive to it than anaerobic bacteria. The inhibitory concentrations of
undissociated acid are as follows: ≤0.01% (100 ppm) for Pseudomonas spp., Sta. aureus, Esc. coli,
and Serratia spp.; ~0.1% for Lactobacillus spp. and Salmonella serovars; and ≤0.02% for most
yeasts and molds, but ~1.0% for Clostridium spp.
The antimicrobial effect of sorbate is produced through its inhibitory action on the functions
of some enzymes, some from the citric acid cycle. It also interferes with synthesis of the cell wall,
protein, RNA, and DNA. Also, like other organic acids, it interferes with the membrane potential
and inhibits spore germination. 2,7
Benzoic Acid
Benzoic acid is used as an acid or sodium salt at 500–2000 ppm (0.05%–0.2%) in many lowpH products, such as nonalcoholic and alcoholic beverages, pickles, confectioneries, mayonnaise and salad dressings, mustards, and cottage cheese. It is more effective against yeasts and
molds than bacteria. The inhibitory effect is produced by both the undissociated and dissociated
acids. The inhibitory concentrations of undissociated acid are 0.01%–0.02% against bacteria
and 0.05%–0.1% against yeasts and molds. The inhibitory action is produced in several ways.
It inhibits the functions of many enzymes necessary for oxidative phosphorylation. Like other
acids, it also destroys the membrane potential. In addition, it inhibits functions of membrane
proteins. 2,8,9