WHO/Food Add./24.65
FAO Nutrition Meetings
Report Series No. 38A
SPECIFICATIONS FOR IDENTITY AND
PURITY AND TOXICOLOGICAL EVALUATION
OF SOME ANTIMICROBIALS AND
ANTIOXIDANTS
The content of this document is the result of the deliberations of the
Joint FAO/WHO Expert Committee on Food Additives which met 8-17
December 1964a
a Eighth Report of the Joint FAO/WHO Expert Committee on Food
Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO
Nutrition Meetings Report Series 1965, 38.
PHOSPHORIC ACID
CHEMICAL NAMES Phosphoric acid; orthophosphoric acid
EMPIRICAL FORMULA H3PO4
MOLECULAR WEIGHT 98.0
DEFINITION Phosphoric acid contains not less than 85% of
H3PO4
DESCRIPTION Clear, colourless, odourless liquid of syrupy
consistency. Miscible with water and ethanol.
NATURAL OCCURRENCE Phosphorus-containing substances occur very
widely in natural foods usually as free
phosphoric acid or as the potassium, sodium or
calcium salts. Phosphate is found in highest
concentrations (0.1-0.5% or more, in terms of
phosphorus) in such foods as milk, cheese,
nuts, fish, meat, poultry, eggs (yolk), and
certain cereals.
USE As a sequestrant, an antioxidant and a
"synergist" for other antioxidants; also as an
acidulant and flavour in beverages and fruit
products.
Biological Data
Biochemical aspects
Phosphoric acid is an essential constituent of the human organism, not
only in the bones and teeth, but also in many enzyme systems.
Phosphorus plays an important role in carbohydrate, fat and protein
metabolism.
The daily intake of phosphate necessary for man lies between 1 and
2 g. Insufficient supply of phosphate produces deficiency in the
bones. Since the phosphate concentration of serum and tissues is
maintained by physiological regulations, the intestinal absorption
depends on requirements and is therefore limited. Doses of 2 to 4 g
act as weak saline cathartics. Excretion takes place mainly in the
faeces as calcium phosphate, so that the continuous use of excessive
amounts of sodium phosphate and phosphoric acid may cause a loss of
calcium.
There have been a great many publications on phosphorus metabolism,1
on the interrelationships of calcium and phosphorus in foods and
nutrition,2 and on the impact thereon of the use of phosphate as a
food additive.3
Short-term studies
Rat. Pathological effects in the parathyroids, kidneys and bones
have been observed in mature male rats fed a diet containing an
excessively high level (8%) of sodium orthophosphate for 7 months or
until the animals succumbed.4 Histological and histochemical changes
in the kidneys have been found in rats fed for 24 to 72 hours on a
diet containing an excess of inorganic phosphate (10% disodium acid
phosphate).5
There are many other reports of adverse effects produced in rats and
other laboratory animals by an excessive intake of inorganic
phosphate.6,7,8,9,10
Three groups of 12 rats each were fed diets containing added dibasic
potassium phosphate so that the calcium and phosphorus concentrations
in the experimental diets were as follows:
Diet Calcium Phosphorus
% %
Control 0.56 0.42
"Normal orthophosphate" 0.47 0.43
"High orthophosphate" 0.50 1.30
The experiment was conducted in three stages, with experimental
observations made when animals had consumed the test diets for 50, 60
and 150 days. No adverse physiological effects were observed
clinically, at autopsy or on histological examination. All the data
obtained from this study indicated that there was probably adequate
absorption and utilization of calcium, phosphorus and iron with both
high and normal levels of orthophosphate.11
Man. Studies on 15 students, who drank 2000-4000 mg of phosphoric
acid in fruit juices every day for 10 days, and on 2 males who
received 3900 mg of phosphoric acid every day for 14 days, revealed no
observable change in urine composition indicative of a disturbed
metabolism.12
Long-term studies
Rat. Three successive generations of rats were fed diets containing
0.4% and 0.75% of phosphoric acid for 90 weeks. No harmful effect on
growth or reproduction could be observed. No significant differences
were noted in the blood picture in comparison with control rats and
there was no other pathological finding which was attributable to the
diets. There was no acidosis, nor any change in the calcium
metabolism. The dental attrition was somewhat more marked than that
in the control rats.13
Comment on experimental studies reported
Phosphoric acid is a material that should not be evaluated solely on
the basis of toxicological studies in animals.
There are strong indications that phosphoric acid should not be used
in such a manner as to result in excessively high phosphorus levels in
the total diet, adverse alterations in the mineral balance of the diet
(i.e. Ca/P ratio), or an appreciable increase in the total mineral
content of the diet as a whole. This is discussed in greater detail
in the Seventh Report of the FAO/WHO Expert Committee on Food
Additives (page 31), where an estimate of the total acceptable dietary
intake of phosphorus from both foods and food additives is made.
However, there is ample evidence to support the safety of the addition
of small quantities of phosphoric acid to food. Thus, the use of
0.01-0.02% as a sequestrant, an antioxidant or "synergist" in
antioxidant mixtures should present no health hazards whatsoever.
Moreover, the use of phosphoric acid to compensate for deficiency of
fruit acidity, as a flavour component, and in other ways, essentially
within the "normal" concentration of phosphates naturally occurring in
foods, should present no problem.
Evaluation
Level causing no significant toxicological effect in the rat
0.75% (=7500 ppm) in the diet, equivalent to 375 mg/kg body-weight per
day.
Estimate of acceptable daily intakes for man
mg/kg body-weight
Unconditional acceptance 0-5
Conditional acceptance 5-15
The total dietary intake of phosphorus from both foods and food
additives should not exceed:
mg/kg body-weight
Unconditional acceptance up to 30
Conditional acceptance 30-70
References
1. McElroy, W. D. & Glass. B., eds. (1952) Phosphorus metabolism - a
symposium on the role of phosphorus in the metabolism of plants and
animals, Baltimore, Johns HopkIns Press, vol. 2
2. Sherman, H. C. (1947) Calclium and phosphorus in food and
nutrition, New York, Columbia University Press
3. Lang, K. (1959) Z. Lebensmitt.-Untersuch., 11O, 450
4. Saxton, J. A., jr & Ellis, G. M. (1941) Amer. J. Path., 17, 590
5. Craig, J. M. (1957) Amer. J. Path., 33, 621
6. House, W. B. & Hogan, A. G. (1955) J. Nutr., 55, 507
7. Maynard, L. A., Boggs, D., Fisk, G. & Seguin, D. (1957) J. Nutr.,
64, 85
8. Selye, H. & Bois, P. (1956) Amer. J. Physiol., 187, 41
9. MacKay, E. M. & Oliver, J. (1935) J. exp. Med., 61, 319
10. Behrens, B. & Seelkopf, K. (1932) Arch. exp. Path., 169, 238
11. Dymsza, H.A., Reussner, G., jr & Thiessen, R., jr (1959) J. Nutr.,
69, 419
12. Laurens, F. (1953) Z. Lebensmitt.-Untersuch., 96, 418
13. Bonting, S. L. & Jansen, B. C. (1956) Voeding, 17, 137