Sulfur dioxide (SO2), sodium bisulfite (NaHSO3), potassium metabisulfite (KHSO3), sodium metabisulfite (Na2S2O5), potassium metabisulfite (K2S2O5), and sodium sulfite (Na2SO3) are allowed as food ingredients in the U.S. These substances are considered as GRAS (Generally Recognized as Safe).
The U.S. Food and Drug Administration (FDA) requires that the presence of sulfites be declared on food labels when used as an ingredient in the food and also when used as a processing aid or when present in an ingredient used in the food (e.g. dried fruit pieces). Sulfites must be declared in these cases when the concentration in the food is ≥10 ppm total SO2. [21 CFR 101.100 (a)(4) "For the purposes of paragraph (a)(3) of this section, any sulfiting agent (sulfur dioxide, sodium sulfite, sodium bisulfite, potassium bisulfite, sodium metabisulfite, and potassium metabisulfite) that has been added to any food or to any ingredient in any food and that has no technical effect in that food will be considered to be present in an insignificant amount only if no detectable amount of the agent is present in the finished food. A detectable amount of sulfiting agent is 10 parts per million or more of the sulfite in the finished food."] If naturally occurring sulfites also exists in foods, it would contribute to the analytical result. Basically, if the food contains ≥ 10 ppm total SO2, then sulfite must be declared on the label. This will most typically occur when sulfite is deliberately added to the food. The specific name of the additive (e.g. sodium bisulfite) must be declared in the case of use as an intentional ingredient.
Sulfites are also prohibited from certain uses in the U.S. Sulfites may not be used in products such as meats that serve as a good source of vitamin B1 because sulfites can scavenge that vitamin from foods. In 1986, following the identification of numerous cases of sulfite-induced asthma occurring on ingestion of green or fruit salads treated with sulfites, FDA prohibited the use of sulfites on fruits and vegetables intended to be served raw or presented fresh to the public (Fed. Regist. 51:25021-25026, 1986). The only exception is sulfite use on minimally processed potatoes sliced or shredded for frying where sulfite use is still permitted (although FDA has a long-standing, though never finalized, proposal to ban that use also). Sulfite use as a fungicide during the shipment of fresh table grapes is regulated by the U.S. Environmental Protection Agency, but the concentration of SO2 residues on the table grapes as consumed must be <10 ppm total SO2.
The labeling of the presence of sulfites on alcoholic beverages is under the jurisdiction of the Tax and Trade Bureau (TTB) of the U.S. Dept. of Treasury. While most ingredients in alcoholic beverages are not declared on the container, the presence of sulfites must be declared. Sulfites are commonly used in wine fermentation to control undesirable growth of acid-producing bacteria while allowing alcohol-producing yeast to proliferate.
Total SO2 levels in foods and beverages should be determined by the optimized Monier-Williams distillation-titration procedure, a method approved by the Association of Official Analytical Chemists (AOAC). Alternate methods do exist but FDA and other federal agencies will typically use the AOAC method so any alternative method must provide similar results.
Food products that contain undeclared sulfites at levels above 10 ppm total SO2 will be subject to potential recall actions. In the U.S., three recall categories are used:
- Class I recalls are the most serious and involve situations where there is a reasonable probability that exposure to the violative product will cause serious adverse health consequences or deaths. FDA is aware of deaths occurring among sulfite-sensitive asthmatics.
- Class II recalls include situations where exposure to the violative product may cause temporary or medically reversible adverse health consequences or where the probability of serious adverse health consequences is rare.
- Class III recalls includes situations where exposure to the violative product is not likely to cause adverse health consequences.
For sulfites, recalls can fall into any of the 3 recall classifications. Using data from controlled oral clinical challenges of sulfite-sensitive asthmatics, the FDA has established dose levels that are associated with Class I, Class II, or Class III recalls. Analysis is done for total SO2 based upon the AOAC procedure. The analytical result is given in terms of a concentration (ppm). FDA determines a worst case dose (mg SO2 equivalents) by using the 95th percentile level of consumption of the food in question. Dose estimates are based upon single occasion exposures. The estimated 95th percentile sulfite ingestion dose (in mg) for a single occasion is then obtained by multiplying the sulfite concentration of the food product (in ppm or mg per kg of food) by the 95th percentile level of food consumption (in kg) for the specific food.
|Class||Est. 95th Percentile Dose|
|Class I||≥10 mg|
|Class II||3.7 - 9.9 mg|
|Class III||< 3.7 mg|
Timbo B, Koehler KM, Wolyniak C, Klontz KC. 2004. Sulfites - a Food and Drug Administration review of recalls and reported adverse events. J Food Prot 67:1806-1811.