I Solfiti comprendono l’anidride solforosa (SO₂) e i relativi sali: solfiti (SO₃²⁻), bisolfiti (HSO₃⁻) e metabisolfiti (S₂O₅²⁻). In Europa sono classificati come additivi E220–E228 e valutati come classe unica per le funzioni conservative, antiossidanti, anti-imbrunimento ed antimicrobiche.

Forme E Impieghi Tipici
I Solfiti sono impiegati in vinificazione per contenere ossidazioni e cariche microbiche, nella frutta secca/disidratata per prevenire l’imbrunimento, nei prodotti a base di patata, nei succhi e nei crostacei per inibire la melanosi; l’efficacia dipende dalla matrice, dalla temperatura e, soprattutto, dal pH del mezzo. Nel vino si distingue tra SO₂ “libera” e “totale”, concetti chiave per la qualità. EFSA Online 

Meccanismi D’azione
I Solfiti inattivano specie ossidanti e radicaliche, bloccano la polifenolossidasi responsabile dell’imbrunimento e reagiscono con carbonili (per esempio l’acetaldeide) formando addotti incolori; la frazione molecolare di SO₂, più presente a pH acidi, è la più attiva anche sul piano antimicrobico. Nel vino, parte della SO₂ può formarsi naturalmente durante la fermentazione e restare in forma combinata. 

Sicurezza Alimentare Ed Esposizione
Allergene. A Livello tossicologico, JECFA ha stabilito una ADI di gruppo pari a 0–0,7 mg/kg peso corporeo/die (espressa come SO₂) per SO₂ e sali correlati; EFSA ha confermato nel 2016 e nel seguito del 2022 che in alcuni scenari di consumo elevato l’esposizione può superare l’ADI temporanea, richiedendo dati più granulari sulle occorrenze. Reazioni avverse includono broncospasmo in una sottopopolazione di asmatici, orticaria e disturbi gastrointestinali. 

Quadro Regolatorio Ed Etichettatura
Nell’Unione Europea “Anidride solforosa e solfiti” rientrano tra le sostanze da dichiarare in etichetta quando superano 10 mg/kg o 10 mg/L espressi come SO₂ totale, calcolati sul prodotto pronto al consumo o ricostituito. Negli Stati Uniti, in modo analogo, la dichiarazione è richiesta a ≥ 10 ppm nel prodotto finito quando i solfiti hanno funzione tecnologica. Nei vini, i limiti massimi di SO₂ totale sono allineati agli standard OIV e recepiti nella normativa UE, con soglie differenziate per tipologia e tenore zuccherino. 

Qualità Di Processo E Metodi Analitici
La Gestione ottimale richiede materie prime idonee, dosi minime efficaci, controllo di pH e ossigeno disciolto, e packaging a barriera. Per il monitoraggio si impiegano misure di SO₂ libera e totale con metodi ufficiali (per esempio aerazione-ossidazione, Monier-Williams e metodi OIV per vini), utili anche a discriminare derive ossidative e rischi sensoriali. 

Aspetti Sensoriali E Difetti
Livelli Eccessivi di SO₂ possono generare sensazioni pungenti, note “fiammifero spento” o “vernice” e mascherare l’aroma varietale; una gestione attenta di pH, ossigeno, tempo e chiusure riduce il rischio, mantenendo al contempo la protezione antiossidante e antimicrobica.

Alternative Tecnologiche E Strategie Di Riduzione
Quando Possibile, l’industria combina buone pratiche igieniche, controllo dell’ossigeno, basse temperature, atmosfera modificata, acido ascorbico/citrico o altri ostacolanti per ridurre il fabbisogno di solfiti. In enologia, scelte su inoculi, gestione del lievito e filtrazioni mirate consentono di contenere le dosi senza compromettere la stabilità microbiologica. 

Sostenibilità E Comunicazione Al Consumatore
Una Comunicazione chiara dell’etichettatura e delle ragioni tecnologiche dell’uso dei solfiti favorisce scelte consapevoli, mentre filiere con controllo dei residui, tracciabilità e processi efficienti riducono sprechi e migliorano l’impronta ambientale, specie in categorie sensibili come vino e frutta disidratata. 

Conclusione
I Solfiti Restano strumenti tecnologici efficaci e versatili per qualità e sicurezza, ma richiedono una gestione rigorosa, un monitoraggio analitico appropriato e un rispetto scrupoloso dei requisiti regolatori e informativi. Un approccio “minimo efficace”, integrato da misure di processo e alternative non solfitanti, consente di mantenere la protezione desiderata riducendo al contempo gli effetti indesiderati e i rischi per i consumatori suscettibili.

Bibliografia__________________________________________________________________________

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).