Phosphoric acid

Phosphoric acid (E338) is a mineral acid produced industrially by wet-process treatment of phosphate rock or by combustion of elemental phosphorus. In food applications it serves as an acidulant, providing the characteristic sharp, tangy taste of cola beverages distinct from the rounder sourness of citric acid. It also functions as a pH control agent, chelating agent, and flavour modifier in processed cheeses, meat products, and certain confectioneries. Phosphoric acid is the primary acidulant in cola soft drinks globally, appearing in concentrations sufficient to lower beverage pH to 2.5–3.0 — more acidic than most other carbonated beverages.

JECFA has established a group ADI of 70 mg/kg body weight per day for phosphoric acid and phosphate salts (expressed as phosphorus equivalents, evaluated 1982). This ADI is generous relative to typical dietary exposures, as phosphorus is an essential mineral; the ADI is established to prevent adverse effects from imbalanced calcium:phosphorus ratios rather than direct phosphate toxicity. The critical issue is not the ADI in isolation but the ratio of phosphorus to calcium in the diet: high phosphate intake with inadequate calcium depresses calcium absorption and can suppress parathyroid hormone regulation of bone mineralisation. Epidemiological studies have associated high cola consumption with reduced bone mineral density in adolescent girls and postmenopausal women, though the relative contributions of phosphoric acid versus sugar and caffeine displacement of milk intake remain debated.

Phosphoric acid is authorised in the European Union under Regulation (EC) No 1333/2008, with maximum permitted levels of 700 mg/kg (as phosphorus) in soft drinks and higher levels in other applications. FDA permits it under 21 CFR §182.1073 with GRAS status. Dental enamel erosion is a documented concern given the very low pH of cola beverages; the combination of phosphoric acid and carbonic acid at pH 2.5 is capable of dissolving enamel hydroxyapatite on prolonged contact. Health authorities generally recommend limiting consumption of phosphoric acid-containing beverages, particularly among populations with osteoporosis risk.