Sulfites comprise sulfur dioxide (SO₂) and its related salts—sulfites (SO₃²⁻), bisulfites (HSO₃⁻), and metabisulfites (S₂O₅²⁻). In the European Union they are authorized as food additives E220–E228 and assessed as a functional class primarily for antioxidant, anti-browning, and antimicrobial purposes. 

Forms And Typical Uses
Sulfites are widely applied across supply chains: winemaking (control of oxidation and microbial loads; stewardship of yeasts and bacteria), dried or dehydrated fruits (browning control), potato products, juices and concentrates, and crustaceans (blackspot inhibition). Efficacy depends strongly on pH, matrix, and time/temperature in processing and storage; in wine technology one distinguishes “free” versus “combined/total” SO₂, a central quality concept. 

Mechanisms Of Action
Chemically, sulfites quench reactive oxygen species, inhibit polyphenol oxidase (browning), and form colorless adducts with reactive carbonyls such as acetaldehyde. In microbiology, the uncharged molecular SO₂ is the most potent form because it diffuses across cell membranes; the molecular fraction increases as pH decreases, which is why pH control is pivotal in oenology and other acidic foods. 

Food Safety And Exposure
Allergen. From a toxicological standpoint, EFSA’s 2016 re-evaluation set a temporary group ADI of 0–0.7 mg SO₂-equivalents/kg body weight/day, confirmed in a 2022 follow-up that also noted potential exceedance in high-intake consumers and called for improved occurrence data. Adverse reactions are well documented in a susceptible subset—particularly some individuals with asthma—ranging from bronchospasm to urticaria and gastrointestinal symptoms. 

Regulatory And Labeling Framework
In the EU, “sulfur dioxide and sulfites” must be declared when present at >10 mg/kg or 10 mg/L (as total SO₂) in the food as sold or as reconstituted, and they are listed among substances requiring mandatory indication to inform allergic or intolerant consumers. In the United States, sulfiting agents that are present in standardized or non-standardized foods at ≥10 ppm (as total SO₂) must be declared under 21 CFR provisions—even when functioning as incidental additives with no technical effect in the finished product. 

Process Quality And Analytical Methods
Sound practice aims for the minimum effective dose alongside control of pH and dissolved oxygen and the use of barrier packaging. Monitoring distinguishes free and total SO₂ and commonly employs the Optimized Monier–Williams procedure (AOAC 990.28) or aeration-oxidation approaches; method selection should consider matrix interferences and the different decision-making roles of free versus total metrics. 

Sensory Aspects And Defects
Excess SO₂ may yield pungency or “struck match/paint” notes and can mask varietal or category character, whereas well-tuned dosing and oxygen management preserve freshness and color without sensory penalties. The pH-linked molecular/free balance also helps explain why seemingly “equal” additions behave differently across products. 

Alternatives And Reduction Strategies
When feasible, manufacturers combine hygienic design and sanitation, temperature control, oxygen management, modified atmospheres, and adjuncts such as ascorbic acid or citrate buffers to lower sulfite needs. In wine, contemporary guidance emphasizes limiting pre-fermentation additions and relying on robust fermentation management and filtration to reduce overall totals while maintaining microbiological stability. 

Sector-Specific Limits (Wine As An Example)
International and EU frameworks specify maximum total SO₂ limits that vary with style and residual sugar. Common reference values include about 150 mg/L for dry reds and 200 mg/L for dry whites and rosés, with 185 mg/L for quality sparkling wines and higher allowances for certain sweet wines; competent authorities may authorize adjustments under defined conditions. These benchmarks illustrate the intersection of safety, quality, and sensory acceptability in a regulated product. 

Conclusion
Sulfites remain versatile and effective tools for quality and safety, provided they are applied judiciously with tight analytical control, precise pH and oxygen management, and scrupulous compliance with labeling rules. An evidence-based “minimum effective” philosophy—supplemented by process and packaging strategies—allows producers to secure oxidative and microbiological stability while mitigating sensory risks and safeguarding susceptible consumers.

References__________________________________________________________________________

Stammati A, Zanetti C, Pizzoferrato L, Quattrucci E, Tranquilli GB. In vitro model for the evaluation of toxicity and antinutritional effects of sulphites. Food Addit Contam. 1992 Sep-Oct;9(5):551-60. doi: 10.1080/02652039209374109. 

Abstract. The food preservatives, sulphur dioxide and its salts, are known to present some toxic, mutagenic and antinutritional effects; in fact they interact with a number of nutrients, e.g. some vitamins, notably thiamine (Th) and folic acid (FA). The effect of different concentrations of sodium bisulphite in cell culture media has been studied in vitro on a human cell line, HEp-2, deriving from a carcinoma of the larynx. Moreover, the sulphites have been tested with different levels of Th and FA with the aim of elucidating how much the cellular response depended on either the anti-nutritional effect or the toxicity of sulphites. Cell growth has been taken as an index of cytotoxicity and measured both as total protein content and as colony-forming ability. With no Th and FA in the culture medium, a clear decrease of cell growth was observed either with or without addition of sodium bisulphite. A dose-dependent reduction of protein content was detected in cells treated with 10, 50, 100, 200, 250 or 500 microM sodium bisulphite. Moreover, when the cells were treated with 10 or 100 microM of this compound, the colony-forming ability was reduced both in number and colony size. As far as the interaction of the two vitamins with sodium bisulphite is concerned, when these nutrients were present in the medium at 0.5, 1.0, 1.5, 2.0 or 2.5 mg/l, a similar growth profile, determined from their concentration, was observed in treated and control cells, the growth levels being affected by the sodium bisulphite contents. At higher levels of Th and FA, the growth index was still increasing only in treated cells, this phenomenon being particularly evident in cultures treated with 200 microM sodium bisulphite. The colony-forming ability was reduced in controls but still increased in treated cells at the highest concentration of vitamins.

Iammarino M, Di Taranto A, Ientile AR. Monitoring of sulphites levels in shrimps samples collected in Puglia (Italy) by ion-exchange chromatography with conductivity detection. Food Addit Contam Part B Surveill. 2014;7(2):84-9. doi: 10.1080/19393210.2013.848943.

Abstract. In shrimps the treatment with sulphiting agents is currently the best option for controlling Melanosis, which is a visual defect of the products that compromises marketability. However, sulphites may cause pseudo-allergic reactions in humans. In this study, 210 samples of shrimps were analysed in order to assess the residual levels of sulphiting agents. A quantifiable sulphites concentration was detected in 76 samples, and these concentrations were higher than the legal limits in eight samples. Considering the important pseudo-allergenic effects caused by these food additives, the non-negligible percentage of 3.8% and the high levels registered in non-compliant samples (up to 1174.1 mg kg(-1)), a strong contrast action based on permanent controls is necessary. Moreover, the levels measured in whole samples were up to four times higher than in the edible parts. These results suggest to consider the introduction of legal limits, related to sulphurous anhydride in the whole product.

Bemrah N, Vin K, Sirot V, Aguilar F, Ladrat AC, Ducasse C, Gey JL, Rétho C, Nougadere A, Leblanc JC. Assessment of dietary exposure to annatto (E160b), nitrites (E249-250), sulphites (E220-228) and tartaric acid (E334) in the French population: the second French total diet study. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2012;29(6):875-85. doi: 10.1080/19440049.2012.658525. 

Abstract. The results of the assessment of the dietary exposure to annatto, nitrites, tartaric acid and sulphites within the framework of the second French total diet study (TDS) are reported. These 4 additives were selected from the Bemrah et al. study [Bemrah N, Leblanc JC, Volatier JL. 2008. Assessment of dietary exposure in the French population to 13 selected food colours, preservatives, antioxidants, stabilizers, emulsifiers and sweeteners. Food Addit Contam B. 1(1):2-14] on 13 food additives which identified a possible health risk for annatto, sulphites and nitrites and a lack of data for tartaric acid. Among the composite samples selected for the whole TDS, 524 were analysed for additives (a sample was analysed for a given additive when it was identified as a major contributor for this additive only): 130 for tartaric acid, 135 for nitrites, 59 for annatto and 200 for sulphites. Estimated concentrations (minimum lower bound to maximum upper bound) vary nationally from 0 to 9 mg/kg for annatto, 0 to 420 mg/kg for tartaric acid, 0 to 108 mg/kg for sulphites and 0 to 3.4 mg/kg for nitrites. Based on the analytical results, the dietary exposure was calculated for adults and children, separately, using lower bound and upper bound assumptions. The European ADIs for these 4 additives were not exceeded except for the dietary exposure for sulphites among 2.9% of the adult population, where the major contributors were alcoholic drinks and especially wine under both hypotheses (lower and upper bound).