SODIUM POTASSIUM TARTRATE

CAS: 304-59-6 EMULSIFIER OR EMULSIFIER SALT, PH CONTROL AGENT, SEQUESTRANT

**Sodium Potassium Tartrate** is a crystalline salt derived from tartaric acid used in food processing for its capacity to act as an emulsifier salt, pH control agent, and sequestrant. It is recognized by regulators in multiple jurisdictions and appears on food additive lists where it supports stability and texture.

What It Is

Sodium Potassium Tartrate is a double salt of tartaric acid, consisting of both sodium and potassium ions bound to the tartrate anion. In food science terms, this substance functions primarily as an emulsifier salt, a pH control agent, and a sequestrant, which means it helps bind metal ions that might otherwise catalyze undesirable reactions in food systems. The additive is often encountered under several other names including Rochelle salt, potassium sodium L(+)-tartrate, and related chemical descriptors reflecting its molecular structure and stereochemistry. The CAS registry number assigned to this compound is 304-59-6, confirming its identity in chemical inventories and regulatory lists. These identifiers are used globally in safety databases and regulatory frameworks to ensure consistent recognition across food safety systems. Sodium Potassium Tartrate has been historically known in chemistry for roles beyond food, such as in laboratory reagents and industrial applications, but its food use is focused on its physicochemical properties. The compound appears as colorless crystals or a white powder with a mildly saline or cooling taste, and it dissolves readily in water, creating solutions that can modify acidity and interact with metal ions. As part of the broader class of tartrate salts, it shares functional similarities with other tartrates used in food, but the mixed sodium-potassium form has specific utility where both sodium and potassium ions contribute to the desired technological effect. Its status as a permitted food additive in regulatory inventories, including the US Code of Federal Regulations, reflects assessments by expert bodies regarding both its chemical identity and its role in facilitating food processing. The range of names under which it may be listed on ingredient panels stems from different naming conventions across jurisdictions and labeling systems, making it important for food scientists, regulators, and consumers to be aware of these synonyms when reviewing product information.

How It Is Made

The manufacture of Sodium Potassium Tartrate for food-grade use begins with tartaric acid, a naturally occurring organic acid found in many fruits, especially grapes. Industrial production typically involves neutralization of tartaric acid with controlled amounts of sodium- and potassium-containing bases such as sodium hydroxide and potassium hydroxide. By carefully adjusting the stoichiometry of these neutralizing agents, the mixed sodium-potassium salt crystallizes preferentially in the desired tetrahydrate form. The resulting crystals are then purified, washed, and dried to meet food-grade purity criteria. In practice, the quality of the initial tartaric acid source, the conditions of crystallization, and downstream purification steps are key determinants of the final product's suitability for food use. Food-grade Sodium Potassium Tartrate must meet specification limits for identity and purity, including minimal levels of heavy metals and other contaminants, in accordance with food chemical codices or regulatory specifications referenced by authorities. In the United States, for example, this compound is affirmed as generally recognized as safe (GRAS) when used in food in accordance with good manufacturing practice, which implicitly includes adherence to food chemical specifications that would be defined by compendia such as the Food Chemicals Codex. The controlled crystallization process not only ensures the correct hydration state and particle morphology but also supports batch-to-batch consistency in functional performance. Manufacturers monitor factors such as temperature, solvent composition, and the rate of cooling to optimize crystal quality. Once the crystalline product is isolated and dried, it undergoes quality control testing to confirm compliance with established food additive specifications, including tests for identity, solubility, loss on drying, and permissible limits for trace impurities. The rigorous quality assurance regime ensures that the ingredient performs predictably in food systems and does not introduce unintended chemical or sensory effects when used as intended.

Why It Is Used In Food

Food formulators rely on Sodium Potassium Tartrate for multiple technological roles in processed foods. An important function is its capacity to act as a sequestrant, which means it preferentially binds trace metal ions such as iron and copper that can catalyze oxidative reactions or cause color and flavor instability in food products. By complexing these metal ions, the additive helps protect the organoleptic quality of foods over shelf life and prevents undesirable discoloration or off-notes that might otherwise arise from metal-catalyzed reactions. Another key role is pH control. Food systems often require precise acid-base balance to maintain texture, stability, and microbial safety. Sodium Potassium Tartrate contributes buffering capacity that can moderate changes in pH during production, storage, or consumption. This buffering property also supports consistent performance of other additives and ingredients whose functionality is pH dependent. In emulsified products, the compound assists in maintaining stable dispersions of oil and water phases, thereby enhancing texture and preventing phase separation. Because these functions are not directly related to nutrition or flavor enhancement, Sodium Potassium Tartrate is considered a processing aid and formulation tool. Its utility spans diverse food categories where metal ion control, emulsification, and pH stability are desirable, such as in certain confections, sauces, beverages, and dairy-derived spreads. The selection of this additive in a formulation is driven by the need to achieve specific quality characteristics that might otherwise be difficult to maintain, especially in complex or shelf-stable products. These effects are achieved at low levels that provide technological benefit without contributing significant taste or nutritional load, aligning with its classification as a food additive rather than a nutrient.

Adi Example Calculation

To illustrate how an acceptable daily intake (ADI) might be applied in a practical context, consider an illustrative example involving a hypothetical adult weighing 70 kilograms. Suppose a regulatory body has established an ADI expressed as an equivalent for the class of compounds that includes Sodium Potassium Tartrate. If this ADI were defined as 30 milligrams per kilogram of body weight per day in terms of an equivalent entity such as tartaric acid, a 70-kg adult could theoretically consume up to 2,100 milligrams per day of that equivalent without exceeding the ADI. This calculation is obtained by multiplying the ADI value (30 mg/kg) by the body weight (70 kg) to yield a total daily allowable intake. In real-world risk assessments, estimated additive intakes are derived from food consumption data combined with typical use levels of the additive across relevant food categories. These estimates are then compared to the ADI to confirm that actual exposure remains comfortably below the conservative safety threshold. The purpose of such calculations is not to prescribe a specific intake level for consumers but rather to ensure that even high-end exposure scenarios do not approach amounts associated with adverse outcomes in toxicological studies. This approach allows regulatory authorities to make science-based decisions that protect public health while enabling the continued use of additives that provide technological benefit in food processing.

Safety And Health Research

Safety assessments of food additives such as Sodium Potassium Tartrate focus on toxicological data and exposure scenarios relevant to human consumption. Expert committees, including the Joint FAO/WHO Expert Committee on Food Additives (JECFA), review available studies to characterize potential hazards, dose-response relationships, and appropriate safe intake levels. For INS 337, JECFA has historically evaluated the compound and expressed acceptable intake in terms of tartaric acid equivalents, taking into account functional roles and typical exposure levels from food. Such evaluations incorporate data on absorption, distribution, metabolism, and excretion, as well as findings from short-term and chronic studies in laboratory species. The emphasis in safety research is on identifying levels of exposure that do not produce adverse effects in animal models, then applying uncertainty factors to account for interspecies differences and human variability. In the case of tartrates, available data did not indicate genotoxic or carcinogenic potential at typical exposure levels relevant to food additive use. Studies addressing kidney effects and other endpoints contribute to the weight of evidence that informs expert judgments on safe intake. Regulatory science integrates these findings with exposure estimates based on actual use levels in food categories to ensure that consumer exposure remains well below levels associated with adverse outcomes. Beyond formal expert evaluations, the broader body of toxicological research on tartrates and related salts provides context for safety considerations. These compounds share metabolic pathways with their parent acid, and studies often examine effects across related substances to build a comprehensive understanding of potential risks. While specific data on Sodium Potassium Tartrate may be limited compared to more extensively studied additives, the consistency of results across related compounds supports regulatory confidence in safety when the additive is used as intended. This evidence-based approach underpins the decisions of food safety authorities to include this ingredient in additive lists subject to compliance with identity and purity standards.

Regulatory Status Worldwide

Sodium Potassium Tartrate is recognized by major food safety authorities in several key jurisdictions. In the United States, it is affirmed as a direct food substance that is generally recognized as safe (GRAS) when used in food in accordance with good manufacturing practice. This affirmation appears in the Code of Federal Regulations at 21 CFR 184.1804, which provides identity and specification information and indicates that its use is permitted without specific quantitative limitations beyond typical good manufacturing practice. The regulation describes the compound’s physical form, origin, and approved technological functions, including its roles as an emulsifier and pH control agent, and references authoritative food chemical specifications that manufacturers must meet. Internationally, the compound is listed under the International Numbering System (INS) for food additives as INS 337, indicating recognition as a food additive with established functional uses. It is also associated with the E number E337 in the European Union, which historically denoted approval for use within the EU’s food additive framework. Regulatory actions in the EU have seen re-evaluation of tartrates and related compounds, with scientific assessments by the European Food Safety Authority (EFSA) addressing group acceptable daily intake considerations for tartaric acid and its salts. These evaluations consider overall exposure and toxicological data to inform conditions of use and safety benchmarks for these additives. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has evaluated Potassium Sodium L(+)-tartrate (INS 337) and assigned it a functional class as a food additive. Historical evaluations have expressed an acceptable daily intake range in terms of tartaric acid equivalents, reflecting international scientific assessment of safety. Regulatory status worldwide is informed by these expert assessments as well as by national and regional food laws that incorporate such evaluations into their own authorization lists or specifications. The presence of Sodium Potassium Tartrate in established additive lists and coded frameworks reflects its accepted use in regulated food processing, subject to compliance with identity, purity, and good manufacturing practices.

Taste And Functional Properties

Sodium Potassium Tartrate has subtle sensory characteristics and notable functional behavior that make it suitable for specific roles in food formulations. Organoleptically, solutions of this compound may exhibit a slightly saline or cooling taste, but at the low concentrations typically employed in food processing, these sensory notes are generally imperceptible to consumers. Because it is highly soluble in water, it integrates readily into aqueous phases of formulations, facilitating uniform distribution and consistent functional performance. Functionally, the compound's ability to interact with metal ions is central to its role as a sequestrant. By binding metals such as iron and copper, it limits the catalytic activity of these ions in oxidation–reduction reactions that can degrade color, flavor, and vitamins. The sequestration action also contributes to clarity in beverages and syrups where haze formation from metal complexes would be undesirable. This property supports a clean visual appearance and prolonged stability during storage. In systems where emulsification or phase stability is required, Sodium Potassium Tartrate helps maintain dispersed phases by supporting charge balance and minimizing coalescence of droplets. Its pH buffering capacity contributes to maintaining an environment where other functional ingredients, such as proteins or hydrocolloids, can perform effectively. Additionally, because the compound dissolves readily and does not introduce strong off-flavors, it complements other formulation components without detracting from product taste profiles. Sodium Potassium Tartrate's functional behavior also extends to its performance under thermal processing. It remains stable under typical food processing temperatures and does not decompose or lose efficacy, which makes it reliable in products that undergo pasteurization or cooking. This stability, combined with its water solubility and ionic interactions, underscores its versatility in food technology applications where stability, clarity, and consistent pH are important quality attributes.

Acceptable Daily Intake Explained

The concept of acceptable daily intake (ADI) is central to regulatory assessments of food additives. An ADI represents an estimate of the amount of a substance that can be consumed every day over a lifetime without appreciable health risk, based on toxicological data and expert judgment. For additives like Sodium Potassium Tartrate, ADI values are often expressed in terms of equivalents of the parent acid or related chemical class, reflecting how the compound and its metabolites are handled in the body. Expert bodies such as JECFA evaluate a range of studies, including chronic toxicity, reproductive toxicity, and other endpoints, to identify a no observed adverse effect level (NOAEL) in laboratory animals. An uncertainty factor is then applied to account for differences between animals and humans and variability within human populations. The resulting ADI is expressed in milligrams per kilogram of body weight per day, providing a safety benchmark against which estimated human exposure from food uses can be compared. It is important to understand that an ADI is not a recommended target intake or a threshold that triggers effects if exceeded briefly. Rather, it is a conservative estimate designed to ensure that typical consumption patterns remain well below levels associated with adverse effects. Regulatory authorities use ADIs to guide conditions of use, maximum permitted levels in foods, and risk communication. Consumers, on the other hand, can interpret ADIs as one component of a broader framework ensuring that additives in the food supply have been evaluated with respect to human health.

Comparison With Similar Additives

Sodium Potassium Tartrate shares functional space with several other tartrate-based food additives and related compounds. For example, sodium tartrates (INS 335) and potassium tartrates (INS 336) are also salts of tartaric acid that serve as acidity regulators and sequestrants. Compared to these single-cation tartrates, the mixed sodium-potassium form combines the ionic contributions of both elements, which can influence solubility, ionic strength, and interactions with other ingredients in formulation. While all tartrates function to manage metal ions and pH, formulators may select one over another based on desired sodium or potassium content, labeling considerations, or specific technical effects in a given food matrix. Citric acid (INS 330) is another widely used acidity regulator that also exhibits metal-chelating activity. Unlike tartrates, citric acid provides a distinct sour flavor at higher concentrations and is often chosen when flavor modification is also desired. In products where minimal flavor impact is critical, tartrate salts such as Sodium Potassium Tartrate may be preferred due to their lower sensory footprint. Phosphate-based sequestrants, such as sodium phosphates, offer alternative metal-binding capacity and buffering functions, though phosphate additives can influence mineral balance in nutrition labeling and may interact differently with food components compared to tartrates. Hydrocolloids like alginates or pectins provide stabilizing effects that complement or substitute for emulsifier salts in some applications. These polysaccharide-based ingredients can stabilize dispersed systems and affect texture, but they do not typically provide metal ion sequestration. Pairing tartrate salts with hydrocolloids or other stabilizers can yield multifunctional outcomes, with the tartrate addressing ion control and the hydrocolloid contributing to mouthfeel and viscosity. The choice among these additives depends on the specific textural, sensory, and regulatory goals of the food product, illustrating how Sodium Potassium Tartrate fits into a broader toolkit of formulation aids used in modern food science.

Common Food Applications Narrative

Sodium Potassium Tartrate finds its way into a variety of processed foods where its functional attributes address specific formulation challenges. In confectionery products such as fondants, caramels, and certain sugar-based confectioneries, control of metal ions and pH can influence texture and shelf life. By complexing trace metals, this additive helps maintain consistent appearance and prevents unwanted reactions that could affect sweetness perception or surface quality. In syrups and cordials, the clarity and stability of the liquid are essential to consumer appeal, and Sodium Potassium Tartrate supports these quality traits by minimizing haze and maintaining a stable liquid phase. Beverages, particularly those with fruit flavors or high sugar content, may also benefit from the sequestrant properties of this additive. Metal ion control in these drinks supports color stability and prevents cloudiness that could diminish perceived quality. In baked goods and dessert toppings, pH control can influence dough performance and final texture, making Sodium Potassium Tartrate an ingredient of interest for formulators seeking reliable results. The compound's ability to act as an emulsifier salt further enhances its utility in complex formulas where oil and water phases must be held in harmony. Beyond sweets and beverages, Sodium Potassium Tartrate contributes to the consistency of processed cheese spreads and other dairy-derived products where uniform texture and prevention of phase separation are desired. Its buffering capacity helps maintain conditions that support protein functionality and prevent brittleness or syneresis during storage. In meat products with coatings or seasonings, this additive supports consistent application of water-soluble components and helps prevent metallic off-flavors that can emerge during processing. Across these applications, the common thread is the need for a multifunctional additive that can support stability, texture, and visual quality without introducing pronounced sensory effects. Producers opt for Sodium Potassium Tartrate when these technological benefits align with formulation goals and regulatory allowances in their markets. Its inclusion in diverse food categories reflects the practical challenges of large-scale food production, where even minor contributors to stability can have meaningful impacts on product consistency and consumer satisfaction.

Safety & Regulations

FDA

  • Approved: True
  • Regulation: 21 CFR 184.1804

EFSA

  • Notes: EFSA has re-evaluated tartrates as a group and established a higher group ADI expressed as tartaric acid equivalents; specific numeric values for this additive alone are part of group context.
  • E Number: E337

JECFA

  • Year: 1973
  • Ins Number: 337
  • Adi Display: 0-30 mg/kg bw
  • Adi Mg Per Kg: 30

Sources

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