Thaumatin
1. Identity: Names, Source, and Forms
1.1 Nomenclature
Thaumatin is the collective name for a family of intensely sweet proteins derived from the katemfe fruit.
It is a mixture of closely-related proteins extracted from the fruit of Thaumatococcus daniellii Benth (katemfe fruit).
In the European Union it is assigned the food-additive code E 957; in the United States it is recognized as a flavoring agent under FEMA GRAS 3732.
The fruit was called katemfe or miraculous fruit of Sudan.
It is also known as miracle fruit, miracle berry, Yoruba soft cane, and African serendipity berry.
The commercially manufactured product sold under the trade name Talin® (Tate & Lyle Ltd.) consists predominantly of thaumatin I and II.
1.2 Botanical Source and Plant Description
Thaumatococcus daniellii (Benth), belonging to the family Marantaceae, is a large flowering herb which can grow up to 4 m high and is commonly found in the rainforests of West Africa ranging from Sierra Leone to the Democratic Republic of Congo.
It is a rhizomatous, perennial herb up to 3.5 m high. The ovate-elliptic leaves (up to 60 cm long and 40 cm wide) arise singly from each node of the rhizome. Inflorescences are single or simply branched spikes and emerge from the lowest node. The fruit is fleshy, trigonal in shape, and matures to a dark red-brown colour when fully ripe. At maturity, each fruit contains three black, extremely hard seeds. The seeds are enveloped by a sticky thin, pale yellow basal aril, which contains the sweetening protein thaumatin.
The amount of thaumatins in arils of mature fruit is 30–55 mg/g of fresh weight (about 50% of total soluble protein), varying within a wide range depending on the degree of fruit maturity and origin.
1.3 Isoforms
Naturally occurring thaumatin consists of six closely related proteins (I, II, III, a, b, and c), all with a molecular mass of 22 kDa (207 amino acids).
The predominant proteins in the food additive E 957 are thaumatin I and thaumatin II, present in a ratio of 2:1, each cross-linked by eight disulfide bridges.
The amino acid sequences of thaumatin I and thaumatin II differ by only two residues. The molecular weights of the two proteins are 22,209 and 22,293 g/mol for thaumatin I and thaumatin II, respectively.
1.4 Common Forms and Preparations
Thaumatin is a mixture of intensely sweet proteins (thaumatin I and II), extracted with water from the arils of the fruit of Thaumatococcus daniellii together with minor amounts of plant constituents. It is an odourless, cream-coloured powder and functions primarily as a flavour enhancer and as a high-intensity sweetener.
According to Commission Regulation No 231/2012, thaumatin (E 957) is obtained by acidic aqueous extraction of the arils of the fruit of Thaumatococcus daniellii (Benth) plant.
The resulting product is available commercially in purified powdered form, predominantly as a mixture of the two main isoforms. Because of its high sweetness intensity, only very small amounts—typically in the parts-per-million range—are needed in any given food formulation.
Since the natural production of these proteins is often too expensive, biochemical production methods are currently under investigation. With these methods, recombinant DNA technology is used for the production of sweet proteins in a host organism. The most promising host known today is the methylotrophic yeast, Pichia pastoris.
Thaumatins' current production method through aqueous extraction from this plant and uncertainty of the harvest from tropical rainforests limits its supply while the demand is increasing. Despite successful recombinant expression of the protein in several organisms, no large-scale bioproduction facilities exist.
2. Traditional and Historical Use
2.1 Indigenous West African Use
The pulp of the arils of the fruit contain thaumatin proteins and has been used as a sweetener, flavor modifier, and enhancer in native cuisines in West Africa for more than one hundred years.
The pulp of the katemfe fruit is traditionally used in West Africa to enhance the flavor of sour foods such as bread, fermented palm wine, and acidic fruit sweets, and is generally used to sweeten cuisine. Additionally, katemfe is added to foods like tea, pap (corn porridge), and garri.
Native thaumatins found in the arils of the fruit of Thaumatococcus daniellii have been used for centuries in West Africa as sweeteners and flavor modifiers. There is no ethnobotanical record of ill effects associated with this traditional consumption.
Beyond sweetening, leaf juice is used as a sedative and an antidote to venoms, stings, and bites in traditional folk medicine; the fruit is used as a laxative, while the seeds are utilized as an emetic and for lung issues.
These traditional non-sweetener uses, however, are ethnobotanical reports and have not been validated by controlled scientific studies.
2.2 Early Western Documentation
The sweetness potency of thaumatin was first elucidated by a British surgeon, Daniell (1855).
In 1839, the English army surgeon and botanist W.F. Daniell brought the fruit to England. The sweetness in the fruit had remained when he returned, despite the long journey. Daniell later published an article on thaumatin in a pharmaceutical journal.
Initially, thaumatin was produced in 1972 by van der Wel and Loeve from the fruits of Thaumatococcus daniellii through aqueous extraction.
In the 1970s, Tate and Lyle began extracting thaumatin from the fruit.
In the West, Japan, Australia, Israel and other countries, isolates of the katemfe fruit have been marketed commercially since the mid-1990s under various trade names (e.g., Talin®; San Sweet T-100®), as low-calorie sweeteners and flavor modifiers.
3. Key Constituents and Chemical Characteristics
3.1 Protein Structure
Thaumatin consists of a single chain of 207 normal amino acid residues with eight disulfide bonds and has a molecular weight of about 22,000. It is very soluble in water (600 g/L) and is stable at pH 2.7–6.0 and under pasteurization conditions.
The thaumatins have a normal complement of amino acids, except that histidine is not present. The molecular weights of the thaumatins are approximately 22,000 and their isoelectric points are in the range of 11.5–12.5. There are no unusual side-chains, atypical peptide linkages, or end-groups.
Extensive disulfide cross-linking confers to thaumatin thermal stability, resistance to denaturation, and maintenance of the tertiary structure of the polypeptide chain. The maintenance of tertiary structure is critical to thaumatin's technical function. Cleavage of just one disulfide bridge results in a loss of sweet taste.
It has an energy content of 17 kJ/g (4 kcal/g). However, because it is deployed at parts-per-million concentrations as a sweetener, its caloric contribution in use is negligible.
Like other pathogenesis-related (PR) proteins, thaumatin is predicted to have a mainly beta structure, with a high content of beta-turns and little helix.
Thaumatins are pathogenesis-related (PR) proteins, which are induced by various agents ranging from ethylene to pathogens themselves, and are structurally diverse and ubiquitous in plants.
3.2 Sweetness Potency
Thaumatin has been rated as approximately 3000 times sweeter than sucrose on a weight basis.
On a molar basis, thaumatin is an intensely sweet-tasting protein that elicits sweet taste at a concentration of 50 nM, a value 100,000 times larger than that of sucrose on a molar basis.
The taste characteristics are the slow onset of sweetness and a sweet aftertaste.
In the mouth, thaumatin exhibits a distinctive long-lasting sweetness coupled with a lingering aftertaste reminiscent of liquorice.
At high concentrations, it exhibits a long-lasting sweet effect that might not be considered acceptable to some palates.
3.3 Key Residues Governing Sweetness
Of the amino acid residues, Lys67 and Arg82 were particularly important for eliciting sweetness.
Research using site-directed mutagenesis has further defined the surface residues involved. Studies focused on three lysine residues (Lys78, Lys106, and Lys137), which were expected to be part of the interaction sites. Three thaumatin mutants (K78A, K106A, and K137A) were prepared and their threshold values of sweetness were examined. The results showed that the sweetness of K106A was reduced by about three times and those of K78A and K137A were reduced by about five times when compared to wild-type thaumatin.
3.4 Physical and Chemical Stability
The protein is heat stable to 70 °C, but loses its sweetness at higher temperature.
It is successfully applied in canning of pet food where it remains stable at temperatures of 120°C and in coatings subjected to dry temperatures of 140°C. Thaumatin is stable under pasteurisation and UHT conditions.
Its stability under acid conditions, to lower than pH 2, is a useful feature — a result of its molecular structure.
4. Mechanism of Action: Sweet Taste Transduction
4.1 The T1R2/T1R3 Sweet Taste Receptor
Current knowledge is that a single receptor accounts for the sweet taste of all sweet molecules, from sugars to sweet proteins: it is a metabotropic G-protein-coupled receptor (GPCR) composed of two similar peptide chains, T1R2 and T1R3.
Typically, a metabotropic GPCR is formed by three domains: a Venus flytrap domain (VFTD), a cysteine rich domain (CRD), and a seven helices transmembrane domain (TMD).
Small-molecule sweeteners typically bind within the VFTM of T1R2 and T1R3.
4.2 The Wedge Model
Considering that the molecular volumes of thaumatin and aspartame can be estimated as 27,000 Ă…Âł and 270 Ă…Âł, respectively, it is difficult to imagine that sweet proteins can bind to the same sites of the sweet receptor that bind small ligands. The first interpretation of the mechanism of interaction of sweet proteins with the sweet receptor was proposed by Temussi soon after the discovery of the sweet receptor. This mechanism is known as the "wedge model".
Small molecular weight sweet compounds shift the equilibrium by entering one or two of the orthosteric sites inside the VFT domains. Larger molecules like sweet proteins achieve the same result by binding to a secondary, external site of the active form.
The preferential interaction with the VFTM in the closed state aligns with the wedge model of receptor activation, which proposes that sweet proteins stabilize a closed, clamshell-like receptor conformation to trigger signaling.
In the case of thaumatin, the region interacting with the receptor is approximately coincident with the so-called cleft-containing face of the protein. The two most important basic residues, namely K67 and R82, are at the center of this region and are surrounded by six acidic residues: D21, E42, D55, D59, D60, and E89.
Cell-based assays suggested that the amino-terminal domain of T1R2 is required for responses to monellin, brazzein, aspartame and neotame, and the CRD of human T1R3 is essential for response to brazzein and thaumatin.
Five amino acid residues in the CRD of T1R3 are important for the response to thaumatin.
The complex model between the T1R2-T1R3 sweet receptor and thaumatin depends critically on the complementarity of electrostatic potentials.
Research using a D21N mutant demonstrated that removing a specific negative charge at residue Asp21 enhances thaumatin's sweetness: the D21N mutant, with a threshold value of 31 nM, is much sweeter than wild-type thaumatin and, together with the Y65R mutant of single chain monellin, is one of the two sweetest proteins known so far.
4.3 Pathogenesis-Related (PR) Protein Classification
Plant thaumatin-like proteins (TLPs) are classified as pathogenesis-related protein family 5 (PR5) due to their induced expression under the invasion of pathogens and pests.
Pathogenesis-related proteins (PR-proteins) are induced in response to environmental stresses such as osmotic and drought stress, wounding, microbial infections and treatment with specific plant hormones and elicitors.
The proteins are involved in systematically-acquired stress resistance and stress responses in plants, although their precise role is unknown.
The sweet-tasting thaumatin from T. daniellii is thus the founding member of a broad protein superfamily found across the plant kingdom, though only the native form from katemfe is intensely sweet; all of the TLPs (thaumatin-like proteins from other plants) lack the sweet tasting property of thaumatin.
5. Scientific Evidence by Area of Use
5.1 High-Intensity Sweetening and Flavor Enhancement
Thaumatin's primary evidence-based application is as a high-intensity sweetener and flavor modifier. Thaumatin is primarily known as a high-intensity sweetener. However, the FDA classifies it as a flavoring agent.
Thaumatin is listed in the Codex General Standard for Food Additives and permitted for general use in food (Codex Alimentarius 2016).
Thaumatin (E 957) is authorised in the EU in 15 food categories with maximum permitted levels (MPLs) ranging from 0.5 to 400 mg/kg and at quantum satis (QS) in the three food categories of table-top sweeteners.
The taste-modifying mechanism that makes it particularly valuable in food formulation is its function as a flavor enhancer and bitterness masker, which operates at sub-threshold sweetening concentrations. This versatile ingredient has a wide range of applications in foods and drinks and particularly in the field of taste modification and flavour enhancement.
The body of evidence supporting its sweetening function is very strong, grounded in decades of food science, sensory evaluation, and regulatory review. Evidence for specific health-promotion effects in humans is limited and discussed below.
5.2 Blood Glucose and Glycemic Effects
Evidence type: Preclinical (animal) and mechanistic/biochemical; clinical human evidence is limited.
While thaumatin has been widely used as a flavor modifier and sweetener, clinical studies specifically investigating its direct health benefits are limited. Some research suggests that, due to its protein nature, thaumatin is unlikely to impact blood glucose levels.
A rat study found that thaumatin did not alter glucose tissue utilisation after 3 weeks of administration: thaumatin did not alter glucose tissue utilisation after 3 weeks.
People with impaired fasting glucose or impaired glucose tolerance were approximately 5–10 times more likely to develop diabetes within one year than normal people. Hence, using alternative sweeteners like thaumatin can contribute to maintaining a healthy diet and avoiding development of diabetes.
This reasoning is mechanistic, not derived from controlled human clinical trials specifically investigating thaumatin's glycemic effects. Overall, the glycemic data for thaumatin specifically are based on animal studies and biochemical reasoning; dedicated human clinical trials are absent from the published literature.
5.3 Non-Cariogenicity (Dental Health)
Evidence type: Regulatory conclusion; no dedicated human clinical trials identified for thaumatin specifically.
Thaumatin has a low calorific value and is non-cariogenic.
Natural compounds such as stevia, monk fruit, or thaumatin are non-cariogenic and have been used as sugar substitutes in foods and beverages aimed at reducing caloric content and glycemic impact.
Non-cariogenicity is attributed to the fact that thaumatin is a protein, not a fermentable carbohydrate; it is not metabolized by oral bacteria in a way that generates acid attack on tooth enamel. No dedicated randomized controlled trials evaluating thaumatin's effect on caries rates in humans were identified in the literature.
5.4 Thaumatin-Like Proteins (TLPs) and Antifungal Activity
Evidence type: Preclinical in vitro and in vivo (plant systems); no human clinical evidence.
While the sweet protein thaumatin from T. daniellii is the namesake of the broader thaumatin-like protein (TLP/PR-5) family, it is the TLP family members from other plants that have been most studied for antifungal properties—not thaumatin itself as a dietary supplement. TLPs are able to rapidly accumulate to high levels in response to biotic or abiotic stress and exhibit antifungal activity in various plant species.
Some of the recombinant PR5 proteins that have been purified are antifungal. PR5 proteins generally exert their antifungal activity through a very fast and dramatic increase in the permeability of the pathogen's plasma membrane, by disrupting the lipid bi-layer and creating trans-membrane pores.
Transgenic plants overexpressing TLP have been shown to enhance resistance against different pathogenic fungi. In vitro antifungal activity of leaf extracts from transgenic tobacco and grape expressing exogenous TLPs has been reported to inhibit mycelial growth of Pythium aphanidermatum, Rhizoctonia solani, Uncinula necator, Botrytis cinerea, and Elsinoë ampelina.
These findings relate to TLPs as a class in plant biology and are not evidence for antifungal health effects from consuming thaumatin as a dietary sweetener.
5.5 Weight Management and Caloric Reduction
Evidence type: Mechanistic/indirect; no dedicated human clinical trials for thaumatin as a weight-management agent.
There is currently a worldwide trend to reduce sugar consumption. This trend is mostly met by the use of artificial non-nutritive sweeteners.
Thaumatin is deployed at concentrations so small that its direct caloric contribution is negligible, making it a functionally non-caloric sweetener ingredient. However, the broader literature on non-nutritive sweeteners and body weight is mixed: randomized controlled trials have found no consistent evidence that non-nutritive sweeteners alter appetite, glucose levels, or body weight, and no trials in this literature focus specifically on thaumatin.
5.6 Pharmaceutical and Nutraceutical Bitterness Masking
Evidence type: Applied food science and pharmaceutical technology; no formal clinical trial data specific to thaumatin.
Thaumatin is employed industrially as a flavor modifier to mask the bitterness and off-tastes of active pharmaceutical ingredients and nutraceutical compounds. There are many applications for this compound as a flavour modifier and flavour enhancer.
Its use in oral pharmaceuticals and nutraceuticals is well established at the technological level, but no clinical trial evidence specifically quantifying its bitterness-masking efficacy in humans for a given drug was identified.
6. Body Systems and Health Areas Associated with Thaumatin
- Gustatory / Taste system: Thaumatin's primary and best-characterized action is on sweet taste receptors (T1R2/T1R3), where it activates the receptor via the wedge model to elicit an intense and prolonged sweet sensation.
- Metabolic / Glycemic system: By replacing sucrose and other fermentable carbohydrates in food products, thaumatin may support dietary patterns associated with lower blood glucose and insulin exposure, though direct clinical evidence in humans is limited to preclinical studies.
- Oral health / Dental system: As a non-cariogenic sweetener, thaumatin does not provide substrate for acid-producing oral bacteria and thus does not promote dental caries, a conclusion endorsed by regulatory bodies.
- Immune / Plant defense (TLP family): As the founding member of the PR-5 pathogenesis-related protein superfamily, thaumatin defines a class of proteins involved in plant innate immune responses and abiotic stress tolerance, though this is relevant to plant biology rather than human health.
- Respiratory system (occupational exposure only): Evidence exists for potential respiratory sensitization in workers handling thaumatin powder in occupational settings (see Safety section below).
7. Regulatory Status and Approved Uses
7.1 International Regulatory Recognition
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has affirmed the safety of thaumatin, assigning it an "ADI not specified" status, which is the most favorable safety designation.
Thaumatin is nontoxic and makes an insignificant contribution to the normal protein intake. Therefore, the WHO JECFA in 1985 specified it to have no ADI.
Thaumatin is included in the GRAS list of approved natural flavoring agents by the FDA.
Japan has approved thaumatin as a food additive by the Ministry of Health, Labour and Welfare; Australia and New Zealand list it as an approved intense sweetener under Food Standards Australia New Zealand (FSANZ); and Canada permits it for use as a sweetener and flavor enhancer by Health Canada.
7.2 European Union
The 2021 EFSA opinion dealt with the re-evaluation of thaumatin (E 957) when used as a food additive. Thaumatin is a natural plant protein, consisting of thaumatin I and thaumatin II proteins together with minor amounts of plant constituents, obtained by acidic aqueous extraction of the arils of the fruit of Thaumatococcus daniellii.
Thaumatin (E 957) is authorised in the EU in 15 food categories with maximum permitted levels (MPLs) ranging from 0.5 to 400 mg/kg and at quantum satis (QS) in the three food categories of table-top sweeteners.
The Panel concluded that there is no need for a numerical acceptable daily intake (ADI) for thaumatin (E 957) and, based on a margin of safety of 5,417 — considered to be an underestimate — derived using the highest 95th percentile exposure of 0.48 mg/kg bw per day in consumers only, there is no safety concern for thaumatin (E 957) at the regulatory maximum level exposure assessment scenario.
8. Dosage Forms and Reported Dosage Levels
In food and beverage applications, thaumatin is used in extremely small quantities owing to its exceptional sweetness potency. FEMA allows the substance widely at levels of 0.1–0.5 parts per million (ppm).
In finished food and beverage products, thaumatin is present in compositions in amounts between 1–25 ppm in various documented formulations. More specifically, thaumatin is present in certain compositions in an amount of about 2–6 ppm.
In the toxicology studies reviewed by EFSA for the 2021 re-evaluation, no adverse effects were observed in sub-chronic toxicity studies in rats and dogs at the highest dose tested of up to 5,200 and 1,476 mg/kg bodyweight (bw) per day, respectively, and in a prenatal developmental toxicity study up to 2,000 mg/kg bw per day.
Human data consisted of three limited human oral intervention studies and two observational studies (exposure to thaumatin via inhalation). The specific protocols and outcomes of those limited human studies were not disclosed in detail in the EFSA opinion's abstract, and no dose–response data for human efficacy trials were identified.
At the population level, the EFSA 2021 assessment estimated that the highest 95th percentile exposure in consumers only was 0.48 mg/kg bw per day under the regulatory maximum level scenario.
9. Safety Considerations
9.1 Overall Toxicological Profile
EFSA's scientific experts assessed the totality of the available scientific evidence, including toxicological, intake and epidemiological data, and concluded that thaumatin is safe when used as a food additive.
The Panel considered that thaumatin is a digestible protein; adequate exposure estimates were available; there was no concern with respect to genotoxicity.
In the sub-chronic toxicity studies in rats, no effects were observed on testis, uterus, or ovaries. Overall, the repeated dose toxicity studies and a prenatal developmental toxicity study in animals did not identify any adverse effects.
No reproductive, chronic toxicity, or carcinogenicity studies were available at the time of the 2021 EFSA re-evaluation.
9.2 Allergenicity via Oral Exposure
Allergenicity via oral exposure was considered unlikely based on animal studies, but was possible via inhalation based on two observational studies in humans. However, indications of allergenicity of thaumatin (E 957) via inhalation in occupational settings are not considered relevant for dietary exposure.
Due to its proteinaceous nature, the additive is considered to be a respiratory sensitiser. Thaumatin is not irritant to the eyes and the skin. In the absence of data, no conclusion on skin sensitisation could be made.
The Panel recommended that the European Commission consider introducing in the EU specifications for thaumatin (E 957) a new specification limit for the minimum combined content of thaumatin I and II proteins in E 957, a specification limit for yeast, mould counts and Salmonella spp, and lowering the existing maximum limit for arsenic along with the inclusion of maximum limits for mercury and cadmium.
9.3 Digestibility and Metabolic Fate
Among sweeteners, natural sweet proteins are unique in that they are natural, often have high sweetness potency compared to sugar, and decompose into a normal distribution of amino acids on hydrolysis.
Thaumatin is therefore metabolized in the same way as dietary proteins, being hydrolyzed in the gastrointestinal tract to its constituent amino acids. It has an energy content of 17 kJ/g (4 kcal/g). However, given the vanishingly small doses used (typically <1 ppm in the final food), its caloric and metabolic contribution is negligible in practice.
9.4 Data Gaps and Limitations
The current evidence base has several notable limitations. No reproductive, chronic toxicity, or carcinogenicity studies were available for the EFSA 2021 review. Human data were limited to three limited human oral intervention studies and two observational studies (exposure to thaumatin via inhalation), precluding strong conclusions about long-term human safety or efficacy for any health claim. The 2021 EFSA panel also noted that no conclusion on oral allergenicity could be drawn from the available human data.
Clinical studies specifically investigating thaumatin's direct health benefits are limited.
As a result, health claims beyond its function as an approved sweetener and flavor modifier are not currently substantiated by sufficient human clinical evidence.
9.5 Interactions
No specific drug–thaumatin pharmacokinetic or pharmacodynamic interactions have been identified in the peer-reviewed literature reviewed for this article. Because thaumatin is digested as a dietary protein, interactions mediated by competitive protein binding or enzyme inhibition have not been documented. Its primary interactions with other substances are sensory: thaumatin is known to synergize with other sweeteners and to mask bitter taste compounds, which is exploited in food and pharmaceutical applications. No contraindications based on concurrent medication use were identified in the regulatory literature reviewed.
References
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