What is benzoic acid

Benzoic acid is an aromatic carboxylic acid, a fungistatic compound that is widely used as a food preservative. Benzoic acid and its salts are primarily used as food preservatives in acidified foodstuffs and beverages such as fruit juice, soft drinks and carbonated drinks. Information on the stability of the salts of the benzoic acid in food is very limited, but the benzoate anion is chemically stable, and degradation in food or reactions with food components are not anticipated, with the exception of the reaction with ascorbic acid under certain conditions (see benzoic acid hazards below). Benzoic acid occurs naturally free and bound as benzoic acid esters in many plant and animal species. Appreciable amounts have been found in most berries (around 0. 05%). Cranberries contain as much as 300-1300 mg free benzoic acid per kg fruit ¹⁾. Benzoic acid is often conjugated to glycine in the liver and excreted as hippuric acid. Benzoic acid is a byproduct of phenylalanine metabolism in bacteria. Benzoic acid is also produced when gut bacteria process polyphenols (from ingested fruits or beverages).

Benzoic acid (E 210), sodium benzoate (E 211), potassium benzoate (E 212) and calcium benzoate (E 213) are authorized food additives (food preservatives) in the European Union (EU) ²⁾. Currently, benzoic acid-benzoates (E 210–213) are authorized as food additives in the EU with maximum permitted levels ranging from 150 to 6,000 mg/kg in foods. Benzoic acid have previously been evaluated by the EU Scientific Committee on Food (SCF) in 1994 ³⁾ and 2002 ⁴⁾. The Scientific Committee on Food established a group acceptable daily intake (ADI) of 0–5 mg/kg body weight per day for benzoic acid and its salts, also including benzyl alcohol and related benzyl derivatives used as flavorings ⁵⁾. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has evaluated benzoic acid and its salts as food additives on a number of occasions. In 1974, JECFA ⁶⁾ established a group acceptable daily intake (ADI) of 0–5 mg/kg body weight for benzoic acid and its salts, expressed as benzoic acid, which was reconfirmed at its most recent evaluation in 1996 ⁷⁾. JECFA has additionally reviewed benzoic acid as a flavoring substance.

Benzoic acid and its sodium and potassium salts are rapidly absorbed after oral administration. The European Food Safety Authority Panel considered that the absorption, distribution, metabolism and excretion of calcium benzoate will be similar to sodium or potassium salt and, therefore, read-across between the
salts was possible. The results of short-term and subchronic studies on benzoic acid and its salts indicate that their toxicity is low. The European Food Safety Authority Panel considered that the use of benzoic acid and its sodium and potassium salts as food additives does not raise a concern with respect to genotoxicity and, based on read-across, also considered that this conclusion is applicable for calcium benzoate ⁸⁾. Moreover, the European Food Safety Authority Panel noted that the available data did not indicate any carcinogenic potential ⁹⁾. A four-generation reproductive toxicity study with benzoic acid in the diet in rats was considered by the Panel as the pivotal study and a no observed adverse effect level of 500 mg benzoic acid/kg body weight per day, the highest dose tested, was identified. From the aforementioned studies, the European Food Safety Authority Panel derived an acceptable daily intake (ADI) of 5 mg/kg body weight per day (expressed as benzoic acid) using an uncertainty factor of 100.

Benzoic acid is generally recognized as safe; however, adverse effects related to allergic reactions, such as asthma, urticaria, asthma, rhinitis, anaphylactic shock, metabolic acidosis, and convulsions, have been reported in sensitive individuals following oral, dermal, or inhalation exposure to benzoic acid ¹⁰⁾, ¹¹⁾. Information regarding skin reactions caused by benzoic acid in the general population is limited ¹²⁾.

From the regulatory benzoic acid maximum level exposure assessment scenario, the main contributing food categories to the total mean exposure estimates for infants and toddlers were flavored fermented milk products. For children and adolescents, the main contributing food categories were confectionary, flavored drinks and processed fish and fishery products; while, for adults and the elderly, the main contributing food categories were processed fruit and vegetables and sauces.

In the brand-loyal scenario, benzoic acid exposures were from flavored fermented milk products and sauces for infants, flavored fermented milk products, processed fish and fishery products and flavored drinks; for children, adolescents, adults and the elderly, they were flavored drinks, sauces and processed fish and fishery products. In the non-brand-loyal scenario, the main contributing food categories were flavored drinks and sauces for all population groups.

When considering the non-brand-loyal scenario, the main contributing food categories were also processed fruits and vegetables and processed foods for infants; for toddlers, they were unprocessed fruits and vegetables, flavored drinks and processed foods; for children and adolescents, the main contributing food categories were flavored drinks and unprocessed fruits and vegetables and for adults and the elderly, the main contributing food categories were unprocessed fruits and vegetables and coffee, tea, herbal and fruit infusions, chicory.

Benzoic acid manufacturing process

According to Maki and Takeda ¹³⁾, benzoic acid is produced, worldwide, by liquid-phase oxidation of toluene with molecular oxygen. Originally the oxidation reaction was carried out at 140 °C and ca. 0.2 MPa with a cobalt naphthenate catalyst (0.1%). Other oil-soluble cobalt salts were also used as catalysts. The purity of toluene is critical because sulphur compounds, nitrogen compounds, phenols and olefins inhibit the oxidation reaction. The oxidation reaction is a free-radical chain process. Peroxides are reaction intermediates. In a typical modern process, the oxidation is conducted at 165 °C and 0.9 MPa. The pressure of the liquid discharged from the reactor is reduced to atmospheric, and unreacted toluene is recovered. Benzoic acid is purified by rectification. The bottom residue is extracted to recover the cobalt catalyst. In the oxidation reaction, several by-products are formed: benzaldehyde, benzyl alcohol and benzyl benzoate. Other esters, including benzyl formate and benzyl acetate, are also present. Biphenyl and methyl biphenyls are formed in smaller amounts. Small amounts of phthalic acid can also be present. For food and pharmaceutical uses, benzoic acid is upgraded by further processing. Sublimation, recrystallisation and neutralization processes have been proposed. To remove phthalic acid, whose presence is not allowed for food uses, treatment with amines and rinsing is required.

According to industry, ‘production of benzoic acid is by liquid-phase oxidation of toluene in the presence of a cobalt catalyst. Air is the source of oxygen in this free radical reaction. Reaction by-products include benzaldehyde, acetic acid, formic acid and benzyl alcohol. Crude benzoic acid is recovered by distillation’ and ‘for sodium benzoate production sodium hydroxide (caustic soda) is added to benzoic acid’.

Sodium benzoate is produced by the neutralization of benzoic acid with sodium hydroxide ¹⁴⁾. Potassium benzoate is obtained in high yield by reacting an aromatic hydrocarbon solution of benzoic acid, such as that which is obtained from the toluene oxidation process, with potassium hydroxide preferably in concentrated aqueous solution, thereby precipitating solid potassium benzoate ¹⁵⁾. No information was available regarding the manufacture of calcium benzoate; the European Food Safety Authority Panel assumed that it is manufactured similarly, by reaction of benzoic acid with calcium hydroxide, or other calcium salt. The European Food Safety Authority Panel noted that if limestone is the source of calcium carbonate which is used in the production of calcium benzoate, then calcium benzoate could be contaminated with aluminium. In its opinion on the re-evaluation of calcium carbonate (E 170) as a food additive ¹⁶⁾, the European Food Safety Authority Panel noted that limestone may contain aluminium at concentrations up to 190 mg/kg. Therefore, specifications for the maximum level of aluminium in calcium benzoate may be required.

Benzoic acid uses

Benzoic acid is an extensively used food preservative. Benzoic acid is generally effective in controlling mold and inhibiting yeast growth and also in preventing a wide range of bacterial attacks ¹⁷⁾. Benzoic acid preservative prevents or delays nutritional losses due to microbiological, enzymatic, or chemical changes of foods during its shelf life. Benzoic acid is generally recognised as safe. The maximum permitted concentrations of benzoic acid in each type of food are controlled by legislation. And the maximum concentrations reported for benzoic acid added to food for preservation purposes were in the range of 2,000 mg/kg of food ¹⁸⁾. The addition of benzoic acid to yogurt is not allowed, and the amount of benzoic acid in yogurt should not exceed 50 mg/kg ¹⁹⁾.

Benzoic acid and sodium benzoate are also included in the European Union Register of feed additives ²⁰⁾. Benzoic acid is authorized as technological feed additive (acidity regulator) for pigs for fattening (10,000 mg/kg), as zootechnical additive for weaned piglets (5,000 mg/kg) and pigs for fattening (10,000 mg/kg) and as a chemically defined flavoring (125 mg/kg) ²¹⁾.

Benzoic acid safety

The available data on absorption, distribution, metabolism and excretion in animals and humans indicate that benzoic acid and its sodium and potassium salts are rapidly absorbed, primarily in the proximal part of the gastrointestinal tract, after oral administration. Benzoate is conjugated to glycine to form hippuric acid which is excreted in the urine. No studies appear to have been conducted on calcium benzoate, but the European Food Safety Authority Panel considered that calcium benzoate also dissociates into its constituents calcium and benzoate ions in the small intestine. Consequently, the absorption, distribution, metabolism and excretion of this salt will be similar to that of the sodium or potassium salts, despite differences in water solubility. The results of the available short-term and subchronic studies on benzoic acid and its salts indicated that their toxicity is low, with no marked target organ toxicity, although high intakes of benzoic acid may lead to disturbances in the acid/base balance, and benzoic acid at high doses may interfere with intermediary metabolism.

The European Food Safety Authority Panel considered that the use of benzoic acid and its sodium and potassium salts as food additives did not raise a concern with respect to genotoxicity. Based on read-across, the European Food Safety Authority Panel considered that this conclusion is also applicable for calcium benzoate ²²⁾.

The European Food Safety Authority Panel noted that the available carcinogenicity studies on benzoic acid and its salts did not indicate any carcinogenic potential, although they were not conducted in accordance with current test guidelines and had deficiencies both in terms of design and reporting. Overall, given supporting evidence of lack of carcinogenicity of the related substances benzyl alcohol, benzyl acetate and benzaldehyde as described by JECFA, the European Food Safety Authority Panel considered that the data are sufficient to conclude that benzoic acid and its salts did not raise concern with respect to carcinogenicity.

In a developmental toxicity study in rats with benzoic acid by gavage, a no observed adverse effect level (NOAEL) of 160 mg benzoic acid/kg body per day was observed for maternal and developmental toxicity The developmental toxicity studies in rats with sodium benzoate in the diet showed a no observed adverse effect level (NOAEL) of 500 mg/kg body weight per day comparable to the NOAEL of the dietary four-generation reproductive toxicity in rats with benzoic acid.

The four-generation reproductive toxicity study with benzoic acid in the diet in rats was considered by the European Food Safety Authority Panel as the pivotal study, as this study was the longest exposure period as compared to the developmental studies. This study showed no effect on growth, fertility, lactation or survival, and provided a NOAEL, for both the parental animals and the offspring, of 500 mg benzoic acid/kg body weight per day, the highest dose tested.

The European Food Safety Authority Panel noted that benzoic acid and its salts may enhance hypersensitivity and/or cause skin reactions in sensitive people. Furthermore, anaphylaxis and urticaria have also been observed in sensitive individuals following exposure to benzoic acid and its salts at doses below the acceptable daily intake (ADI). Several  studies have shown that subgroups of patients already suffering from atopic dermatitis, pruritus, urticaria or persistent rhinitis may be intolerant even to low doses of benzoate.

The European Food Safety Authority Panel noted the absence of any indication of genotoxicity of benzoic acid and its salts in vivo, together with the negative results of limited carcinogenicity studies in rats and mice. The Panel considered that the acceptable daily intake (ADI) cannot be derived from a prenatal developmental toxicity study with benzoic acid performed by gavage. The developmental toxicity studies in rats with sodium benzoate in the diet, showed NOAELs of 500 mg/kg bw per day (the highest dose tested) and 1310 mg/kg body weight per day, respectively, comparable to or higher than the NOAEL of 500 mg/kg bw per day in the dietary multigeneration reproductive toxicity in rats with benzoic acid. From these reproductive and developmental studies, the European Food Safety Authority Panel derived an acceptable daily intake (ADI) of 5 mg/kg body weight per day (expressed as benzoic acid) applying an uncertainty factor of 100.

In 2008, the European Food Safety Authority Panel on Food Additives, Flavorings, Processing Aids and Food Contact Materials assessed the results of McCann et al. ²³⁾ study that has concluded that exposure to two mixtures of four synthetic colors plus sodium benzoate, as a preservative, in the  diet resulted in increased hyperactivity in 3-year-old and 8- to 9-year-old children in the general population. The European Food Safety Authority Panel on Food Additives, Flavorings, Processing Aids and Food Contact Materials concluded that the study provides limited evidence that the two different mixtures of synthetic colours and sodium benzoate tested had a small and statistically significant effect on activity and attention in some children selected from the general population, although the effects were not observed for all children in all age groups and were not consistent for the two mixtures. The findings may thus be relevant for specific individuals within the population, showing sensitivity to food additives in general or to food colors in particular ²⁴⁾.

Benzoic acid is included in the European Union list of flavorings. Joint FAO/WHO Expert Committee on Food Additives reviewed benzoic acid as a flavoring substance at its 59th meeting, as one of a group of benzyl derivatives, at which the group ADI of 0–5 mg/kg body weight for benzoic acid and related compounds was reconfirmed ²⁵⁾. The European Food Safety Authority Panel has evaluated benzoic acid as a supporting substance in its opinion on benzyl alcohols, benzaldehydes, a related acetal, benzoic acids and related esters from chemical group 23 and 30 ²⁶⁾, in which it was concluded on the basis of the default maximized survey-derived daily intake approach that these substances would not give rise to safety concerns at the estimated levels of intake arising from their use as flavoring substances.

Benzoic acid as a biocide (a chemical substance that destroys any harmful organism) was evaluated by Germany ²⁷⁾ and is permitted for this use according to EU Commission Implementing Regulation 1035/2013 ²⁸⁾.

Benzoic acid and sodium benzoate have also been evaluated by the Scientific Committee on Cosmetic Products and Non-Food Products Intended for Consumers ²⁹⁾ and the Scientific Committee on Consumer Products ³⁰⁾. Additionally, benzoic acid has been reviewed as a pesticide-active substance ³¹⁾.

To assess the dietary exposure to benzoic acid-benzoates (E 210–213) from their use as a food additive, the exposure was calculated based on (1) maximum permitted levels set out in the EU legislation (defined as the regulatory maximum level exposure assessment scenario) and (2) the reported use levels and analytical data (defined as the refined exposure assessment scenario). Dietary exposure through this latter scenario was assessed using two sets of concentration data: reported use levels and analytical data not exceeding the maximum permitted levels for food categories for which direct addition of benzoic acid-benzoates is authorized; and reported use levels and analytical data not exceeding the maximum permitted levels for food categories for which direct addition of benzoic acid-benzoates is authorized and analytical data for food categories which may contain benzoic acid benzoates due to carry-over and for which data were available.

The exposure estimates in the regulatory maximum level exposure assessment scenario exceeded the acceptable daily intake (ADI) of 5 mg/kg body weight per day for all population groups at the high levels and for toddlers and children also at the mean level.

Considering only food categories for which direct addition of benzoic acid-benzoates to food is authorized, the refined exposure to benzoic acid-benzoates (E 210–213) in toddlers and children, exceeded the ADI of 5 mg/kg body weight per day at the high level (95th percentile) in the refined brand-loyal exposure estimate, while, for the non-brand-loyal scenario, the group acceptable daily intake (ADI) was not exceeded in any population group. Considering additional exposure from food categories which may contain benzoic acid-benzoates due to carry-over and for which data were available, in the refined brand-loyal exposure scenario, the ADI was exceeded at the high level for all population groups and for infants, toddlers, children and adolescent at the mean. In the non-brand-loyal exposure scenario, the ADI was exceeded only for toddlers and children at the high level; at the mean level, there was no exceedance.

Considering the present toxicological database the European Food Safety Authority Panel identified a NOAEL of 500 mg/kg body weight per day and applying an uncertainty factor of 100, the European Food Safety Authority Panel derived a group ADI of 5 mg/kg body weight per day, expressed as benzoic acid, for benzoic acid (E 210), sodium benzoate (E 211), potassium benzoate (E 212) and calcium benzoate (E 213).

The Panel concluded that from the use of benzoic acid-benzoates as food additives from direct addition to food, the group ADI was exceeded in the brand-loyal scenario for toddlers and children consuming on a regular basis flavored drinks.

Considering additional exposure from food categories which may contain benzoic acid-benzoates due to carry-over and for which data were available, the Panel concluded that exposure to benzoic acid-benzoates could be increased by up to two to three fold for all high-level consumers compared to the previous scenario for direct addition to food. This results in exceedance of the group acceptable daily intake (ADI) in toddlers and children for the non-brand-loyal scenario. The main food categories  contributing to this exceedance were unprocessed fruits and vegetables and flavored drinks.

Toxicological data

The European Food Safety Authority Panel noted the conclusions of the SCF ³²⁾ and JECFA ³³⁾, that there is evidence of a common and rapid route of metabolism of the salts of benzoic acid and the three benzyl derivatives benzyl alcohol, benzyl acetate and benzaldehyde to benzoic acid and subsequently to hippuric acid. It is therefore reasonable to assume that studies on any of these substances provide valid information for the assessment of the toxicity of benzoic acid and its salts ³⁴⁾, ³⁵⁾. The European Food Safety Authority Panel agreed with this conclusion.

Acute oral toxicity

In its 1996 evaluation, JECFA ³⁶⁾ presented the results of acute oral toxicity studies in rats, rabbits and dogs, showing LD50 (lethal dose 50, where 50% of test subjects die) values for benzoic acid or sodium benzoate ranging from 2,000 to 2,700 mg/kg body weight. At its 57th meeting JECFA reviewed two further acute oral toxicity studies on benzoic acid in mice, one providing a LD50 value of 1,200 mg/kg body weight, and the other a value of 2,000 mg/kg body weight ³⁷⁾.

An acute study with benzoic acid by gavage in male and female mice was available to the European Food Safety Authority Panel. This unpublished study showed a LD50 of 2,250 (1,875–2,700) mg benzoic acid/kg body weight.

An acute study by gavage with benzoic acid in albino rats was available to the European Food Safety Authority Panel. This unpublished study showed a LD50 for males of 2,742 mg benzoic acid/kg body weight and for females of 2,565 mg benzoic acid/kg body weight.

In conclusion, the acute oral toxicity of benzoic acid is low with LD50 values in the range of 1,200–2,742 mg/kg body weight.

Short-term and subchronic toxicity

The results of the available short-term and subchronic studies on benzoic acid and sodium benzoate indicated that the toxicity of benzoic acid and its salts is low with no marked target organ toxicity. The European Food Safety Authority Panel noted however that the majority of available studies were conducted many years ago, and were not in accordance with current test guidelines.

Benzoic acid hazards – formation of benzene from benzoic acid in the presence of ascorbic acid

Small amounts of benzene can be formed from benzoic acid in the presence of ascorbic acid and transition metal ions like copper and iron ³⁸⁾. The chemical reaction is catalysed by metal ions, which are present at low concentrations in drinking water. The studies performed by Chang and Ku ³⁹⁾, Gardner and Lawrence ⁴⁰⁾ and McNeal et al. ⁴¹⁾ were summarized by the German Federal Institute for Risk Assessment ⁴²⁾.

In 2006, the European Commission and Member States had become aware of the potential formation of benzene under certain conditions in soft drinks from the reaction of benzoic acid and other ingredients. The European Food Safety Authority Panel noted that the formation of benzene in beverages containing benzoic acid or its salts as preservatives is linked to certain formulations, such as ascorbic acid in the presence of metallic ions and also to conditions of storage. Therefore, the European Food Safety Authority Panel considered that when benzoic acid or its salts and ascorbic acid are used together, consideration should be given to the storage of soft drinks and food contact materials to minimize the formation of benzene in beverages. The issue was considered in the meetings of the Standing Committee of the Food Chain and Animal Health in July and December 2007 ⁴³⁾, ⁴⁴⁾. “The Committee noted that the reformulation work by the industry appeared to be working given the limited number of samples in which levels of benzene were above 10 μg/L. However it was considered that further monitoring would be useful although no further formal action was considered necessary by the Commission at this time”.

The Norwegian Scientific Committee for Food Safety reported results of analysis of benzene content in 16 soft drinks containing both sodium benzoate and ascorbic acid; 13 samples contained nondetectable levels of benzene and three samples contained benzene at levels between 0.7 and 4.7 mg/L ⁴⁵⁾.

In Germany, the concentrations of benzene measured in non-alcoholic beverages were below the EU drinking water limit of 1 μg/L while higher concentrations were found in previous years ⁴⁶⁾.

Therefore, the European Food Safety Authority Panel considered that combining ascorbic acid with benzoic acid in soft drinks could lead to the formation of benzene from benzoic acid. The European Food Safety Authority Panel noted that benzene is a genotoxic carcinogen classified by the International Agency for Research on Cancer as carcinogenic to humans (Group 1) ⁴⁷⁾, that the World Health Organization (WHO) has derived a guideline value for benzene in drinking water of 10 μg/L ⁴⁸⁾, that according to the Council Directive 98/83/EC12 the maximum level of benzene in drinking water is 1 μg/L in the European Union and that the German Federal Institute for Risk Assessment considered that the concentration of benzene in beverages should be as low as reasonably achievable ⁴⁹⁾.

The European Food Safety Authority Panel recommended that when benzoic acid or its salts and ascorbic acid are used together, consideration should be
given to the storage of soft drinks and food contact materials to minimize the formation of benzene in beverages as low as reasonably achievable.