SODIUM THIOSULFATE

CAS: 10102-17-7 ANTIOXIDANT, FORMULATION AID, OXIDIZING OR REDUCING AGENT, SEQUESTRANT, STABILIZER OR THICKENER

Sodium thiosulfate (CAS 10102-17-7) is an inorganic salt used in foods for antioxidant effects and as a formulation aid, oxidizing or reducing agent, sequestering agent, and stabilizer. It appears in FDA regulation 21 CFR 184.1807 and has been evaluated internationally by JECFA with an assigned INS number 539.

What It Is

Sodium thiosulfate is an inorganic chemical compound identified by the CAS number 10102-17-7 and used in food systems under regulatory reference 21 CFR 184.1807 with multiple functional roles such as antioxidant, formulation aid, oxidizing or reducing agent, sequestering agent, and stabilizer. It is generally encountered in the pentahydrate form in food applications and may be listed by the International Numbering System (INS) as 539 in international additive listings. As an antioxidant it helps delay oxidative deterioration and as a sequestering agent it binds trace metals which can catalyze oxidative reactions. In its typical appearance it is a white crystalline powder or solid in the pentahydrate form. The compound is recognized under regulatory frameworks in the United States as a permitted food ingredient when used in accordance with good manufacturing practice. Its multiple technical designations reflect varied functionalities in food formulation to support quality, stability, and consistency. Other common identifiers that appear in technical and regulatory contexts include synonyms such as sodium thiosulfate pentahydrate, antic​hlor, and disodium thiosulfate pentahydrate, which refer to the same base chemical entity. The additive is distinct from chemically similar sulfite additives though they can be evaluated together under some regulatory safety assessments because of shared functional endpoints.

How It Is Made

Sodium thiosulfate is typically prepared by controlled chemical reactions involving sulfides and sulfur dioxide or by the reaction of elemental sulfur with sulfite salts under defined industrial conditions, yielding the pentahydrate form. According to the U.S. Food and Drug Administration regulatory text for 21 CFR 184.1807, the substance may be synthesized via the reaction of sulfides and sulfur dioxide or by the oxidation of metal sulfides or hydrosulfides, giving a product that meets compendial specifications such as Food Chemicals Codex standards. These pathways are designed to produce a consistent and high-purity product that is suitable for use in food systems. Industrial production of sodium thiosulfate emphasizes control of reaction conditions and purification steps to ensure that the final additive meets food-grade criteria for identity, purity, and the absence of contaminants. The pentahydrate form is commonly commercialized for food applications because it is stable, readily soluble in water, and supports consistent functional performance across a range of food formulations. From a quality and specification perspective, manufacturers producing food-grade sodium thiosulfate align their processes with recognized standards such as those outlined in food additive monographs. These specifications define acceptable levels of impurities and outline analytical methods for verification, ensuring that the additive used in food applications is consistent with regulatory expectations.

Why It Is Used In Food

Sodium thiosulfate is incorporated into food products primarily for its multifunctional roles that support food quality and stability. As an antioxidant it can help slow the oxidative breakdown of lipids and other susceptible components, thereby reducing the development of off-odors, off-flavors, and discoloration that result from oxidation. Its action as a sequestering agent binds trace metals which can accelerate oxidation and degradation, improving shelf life and maintaining product appearance. In addition to these functions, sodium thiosulfate can act as a formulation aid to support the integration of ingredients that might otherwise react unfavorably. Its reducing or oxidizing properties can be leveraged in specific food processing contexts where controlled redox activity is desirable. It also serves as a stabilizer or thickener in certain applications, contributing to product consistency and texture. The compound’s inclusion in regulatory listings such as the FDA’s 21 CFR 184.1807 underscores its acceptance when used in accordance with good manufacturing practice, reflecting both its utility and the need for controlled use. The flexibility of sodium thiosulfate’s roles makes it a useful tool for food scientists in formulating products that meet quality, stability, and sensory expectations.

Adi Example Calculation

To illustrate an ADI concept in a simplified manner (not specific to sodium thiosulfate alone but using a group ADI expressed in sulfur dioxide equivalents), consider a hypothetical adult weighing 70 kilograms. If a group ADI is expressed on a sulfur dioxide equivalent basis, a person weighing 70 kilograms would have a theoretical threshold that regulators consider unlikely to pose health concerns if not exceeded. For example, if the group ADI were expressed as a numerical range or limit in terms of sulfur dioxide equivalents, the calculation would multiply the numeric ADI value by the bodyweight to estimate a maximum total allowable daily exposure. In practice, this hypothetical calculation illustrates how regulators account for body size when interpreting ADIs, though actual use levels in foods and cumulative exposure from multiple sources are also taken into account in detailed dietary exposure assessments. This example serves to demonstrate how ADIs are contextualized in regulatory science rather than provide specific intake guidance. Actual regulatory ADIs are defined by authoritative bodies and must be referenced directly from their evaluations.

Safety And Health Research

Regulatory and safety evaluations of sodium thiosulfate in food contexts focus on its technical function and general toxicological profile rather than direct physiological effects. As an inorganic additive with established functionality in food systems, regulators such as JECFA have included it in group evaluations with related sulfite-type compounds, indicating that its potential effects were considered alongside similar substances under a combined safety assessment expressed in terms of sulfur dioxide equivalents. This group evaluation informs guidance on acceptable intake levels based on cumulative exposure to components with shared functional properties. Toxicological data for related compounds typically examine endpoints such as general systemic toxicity, potential effects on organ systems, and dose-response relationships in laboratory studies. These studies support regulatory assessments that consider both hazard and expected dietary exposure. In practical terms, sodium thiosulfate’s inclusion in regulatory lists reflects assessments that its use at levels consistent with good manufacturing practice does not pose an undue risk, given the compound’s chemistry and use patterns. It is important to note that safety evaluations by expert bodies aim to define conditions under which an additive can be used without exceeding conservative safety thresholds derived from scientific evidence. These evaluations consider available data on absorption, distribution, metabolism, excretion, and potential toxicology, supporting regulatory decision-making.

Regulatory Status Worldwide

In the United States sodium thiosulfate is listed in the FDA’s food additive regulations under 21 CFR 184.1807, which describes its permitted use and identity specifications for food applications. The FDA regulation outlines preparation methods, identity parameters, and references compendial standards such as the Food Chemicals Codex for purity requirements, reflecting its status as a permitted ingredient when used in accordance with good manufacturing practice. This listing supports its use as an antioxidant, sequestering agent, formulation aid, and related technical functions. Internationally, sodium thiosulfate has been evaluated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and appears in the Codex Alimentarius classification with an assigned INS number of 539, indicating recognition in international additive lists. JECFA evaluations group sodium thiosulfate with other sulfite-type additives for a combined safety assessment that expresses an acceptable daily intake in terms of sulfur dioxide equivalents. In the European Union context, while sodium thiosulfate has an INS designation, there is no clear listing in the consolidated EU food additive database, suggesting that specific authorization under current EU food additive regulations may not be established or widely used. This highlights the variability in additive authorizations across jurisdictions, where regulatory bodies assess safety and permitted uses based on local frameworks and definitions of technological need. Producers should consult regional regulatory listings and authorities for details on permitted conditions of use in specific markets.

Taste And Functional Properties

Sodium thiosulfate itself is not added for taste but can influence the sensory profile of foods indirectly through its functional properties. For example, by reducing oxidation it helps preserve the intended flavors and colors of products, minimizing the development of rancidity or discoloration that can detract from sensory appeal. The compound is highly soluble in water, which allows it to disperse uniformly throughout aqueous food systems, performing its sequestering and antioxidative roles effectively. Functionally, sodium thiosulfate operates across a range of pH values and temperatures typically encountered in food processing, though its efficacy in specific applications depends on formulation context and interaction with other ingredients. Its solubility supports incorporation into liquid and semi-solid foods, while its stability under typical processing conditions helps ensure that it retains functionality through manufacturing and storage. Because the compound is not inherently flavorful, it does not contribute a distinct taste, but its stabilizing and antioxidative effects help maintain the intended taste profiles of foods by delaying sensory degradation. Manufacturers consider these properties when selecting sodium thiosulfate for roles where oxidative stability and sequestration of metal ions contribute to maintaining quality attributes over the product’s shelf life.

Acceptable Daily Intake Explained

An acceptable daily intake (ADI) represents a regulatory benchmark used by expert bodies to describe a level of daily exposure to an additive that is not associated with appreciable health risk over a lifetime. For substances evaluated in groups, such as sodium thiosulfate with other sulfite-type compounds, the ADI may be expressed in terms of a common reference such as sulfur dioxide equivalents, reflecting combined exposure considerations. This group-based approach accounts for shared metabolic and toxicological pathways among related compounds. The ADI is derived from toxicological studies, typically in animals, that identify levels at which no adverse effects are observed, and then applying safety factors to account for uncertainties in translating animal data to humans and variability among individuals. It is not a recommended intake but rather a conservative threshold to guide regulatory use and dietary exposure assessments. When evaluating sodium thiosulfate, regulatory bodies consider its contribution to total dietary intake of related substances, ensuring that combined exposure remains below the established ADI expressed for the group. This helps frame safe use in food products while accommodating normal consumption patterns.

Comparison With Similar Additives

Sodium thiosulfate shares functional similarities with other sulfur-containing additives such as sodium sulfite and sodium metabisulfite, which also serve as antioxidants and sequestering agents in food systems. While these compounds all contribute to delaying oxidative changes, they differ in solubility profiles, redox potentials, and regulatory status across regions, which can influence their selection for specific applications. For example, sodium metabisulfite is widely used in wine and dried fruit preservation, whereas sodium thiosulfate may be chosen in formulations where its unique balance of reducing power and sequestration is advantageous. Compared to non-sulfur antioxidants like ascorbic acid, sulfur-based additives provide distinct functional effects in binding metal ions that can catalyze oxidation. Ascorbic acid also acts as an antioxidant but through different chemical mechanisms tied to its vitamin C structure. Manufacturers may select one over the other based on compatibility with other ingredients and the desired sensory outcome. Another additive class with stabilizing properties includes chelating agents such as EDTA (ethylenediaminetetraacetic acid), which binds metal ions to prevent catalysis of oxidative reactions. Sodium thiosulfate’s sequestering role can be contrasted with EDTA’s broader chelation profile, reflecting choices available to formulators based on specific quality goals. Understanding these distinctions helps food scientists match additive functions with formulation needs.

Common Food Applications Narrative

Sodium thiosulfate is used in a range of processed food and beverage applications where its multifunctional properties support product quality. In items that contain fats and oils, it is used to help retard oxidative changes that can lead to rancidity and off-flavors, supporting an extended shelf life and maintaining sensory integrity. In complex formulations such as sauces, dressings, and emulsions, its sequestering action binds trace metal ions that might otherwise catalyze oxidative breakdown, helping to preserve texture and appearance. The ingredient may also be incorporated into beverage systems with components susceptible to oxidation, where maintaining clarity and flavor stability is essential. It can assist in stabilizing color and flavor profiles in products with extended storage or distribution timelines. Additionally, sodium thiosulfate’s formulation aid properties support consistent integration of other ingredients in structured food systems, contributing to texture and homogeneity. While not a direct flavor enhancer, the role of sodium thiosulfate in stabilizing food matrices and preventing unwanted changes helps manufacturers deliver products that meet consumer expectations for quality and consistency. Its use is guided by regulatory frameworks and good manufacturing practices to ensure that formulation objectives are met without compromising food safety or compliance.

Safety & Regulations

FDA

  • Approved: True
  • Regulation: 21 CFR 184.1807

EFSA

  • Notes: EFSA authorization status not clearly identified in public additive databases
  • E Number: 539

JECFA

  • Year: 1998
  • Notes: ADI range derived from JECFA group evaluation for related sulfite additives
  • Ins Number: 539
  • Adi Display: Group ADI expressed as sulfur dioxide equivalents 0-0.7 mg/kg bw

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