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What is Monellin? Unveiling the Sweet Protein and Its Applications

Monellin is a naturally occurring sweet protein discovered in 1969 and found in the fruit of the West African shrub, serendipity berry (Dioscoreophyllum cumminsii). With a sweetness that is approximately 1500-2000 times greater than sucrose, monellin has gained significant interest as a non-caloric sweetener in the food and beverage industry. Despite its intense sweetness, this protein has a peculiar characteristic of having a slow onset of sweetness response and a licorice-like aftertaste.

Monellin’s unique structure, consisting of 94 amino acids, plays a crucial role in its sweet taste. It is this molecular structure that allows the protein to interact with our taste receptors, tricking them into perceiving a sweet sensation. Monellin, along with other sweet proteins, offers an alternative to traditional sugar-based sweeteners, which contribute to obesity and other health issues when consumed in excess.

Key Takeaways

  • Monellin is a natural sweet protein extracted from the serendipity berry, with a sweetness 1500-2000 times greater than sucrose.
  • The protein’s unique structure of 94 amino acids allows it to interact with taste receptors, providing a sweet sensation.
  • Monellin offers potential as an alternative to traditional sugar-based sweeteners due to its non-caloric nature and intense sweetness.

Monellin Origins

Monellin is a sweet protein that was discovered in 1969 and is derived from the fruit of the West African shrub called serendipity berry, or Dioscoreophyllum cumminsii. This plant is native to West Africa, particularly in countries, such as Sierra Leone, Liberia, and Nigeria. The protein was named in 1972 after the Monell Chemical Senses Center in Philadelphia, USA, where it was first isolated and characterized.

The serendipity berry has been used locally for centuries as a natural sweetener primarily due to monellin’s potent sweet taste. Compared to sucrose, which is commonly known as table sugar, monellin is approximately 90,000 times sweeter on a molar basis. This sweet protein has an intense and persistently sweet taste that is highly sought after for its potential applications in food and beverage industries, especially as a sugar substitute for people with diabetes or other dietary restrictions.

While monellin is primarily known for its sweet taste, researchers and food scientists also find interest in its unique structure and the way it interacts with our taste buds to create such an intense sweetness. This ability deserves further research to understand and potentially apply it in the development of new sweeteners or taste-modifying molecules.

In summary, monellin has its origins in the serendipity berry found across West Africa. It has a long-standing history as a traditional natural sweetener and presents promising opportunities for application in modern food and beverage products.

Protein Structure and Properties

Primary and Secondary Structure

Monellin, an intensely sweet protein found in the fruit of Dioscoreophyllum cumminsii, is composed of two peptide chains in its natural form (PDB: 3MON). It has a molecular weight of around 10,000-10,500, which is calculated from its amino acid analysis. The single-chain variant of Monellin, MNEI, is also mainly found in nature. As a secondary structure, Monellin consists of five beta-strands (β-sheet) forming an antiparallel beta-sheet and a 17-residue alpha-helix (α-helix).

Tertiary Structure and Stability

The tertiary structure of Monellin adopts a wedge-shaped architecture, which can be described as a five-strand β-sheet partially “wrapped” around an α-helix. However, Monellin’s stability at high temperatures or extremes of pH is compromised in its natural form due to its two peptide chains.

MNEI, the single-chain variant of Monellin, is more stable at high temperatures and wider pH ranges. It retains the secondary structure elements (α-helix and β-sheet) found in the natural form. This stability aids in the applications of Monellin in the food industry, where heat denatures most proteins.

Overall, Monellin has a compact and well-defined structure, which plays a vital role in its sweet taste properties and potential applications.

Sweetness Mechanism

Interactions with Taste Receptors

Monellin is a sweet protein that originates from the fruit of Dioscoreophyllum cumminsii, also known as the serendipity berry, native to West Africa. This protein, containing 94 amino acids, interacts with sweet taste receptors, specifically the T1R2-T1R3 receptor complex, to provide an intensely sweet taste. Monellin is approximately 1500-2000 times sweeter than sucrose, making it a potential candidate for use in low-calorie sweeteners and diet foods.

When Monellin binds to the sweet taste receptors, it does so in the large cleft surrounding the small sugar binding site. This interaction effectively tricks the receptor into thinking that sugar has bound, resulting in a sweet taste sensation. The sweetness of Monellin is pH-dependent, with the protein being tasteless below pH 2 and above pH 9. Its sweetness also has a slow onset and a lingering aftertaste.

Molecular Determinants of Sweetness

The molecular mechanisms that contribute to Monellin’s sweetness can be partly attributed to its unique amino acid composition and structure. Since only a small amount of Monellin is needed to evoke a sweet taste, it is efficient in creating low-calorie and sugar-free foods, which could benefit people needing to reduce their sugar intake or those with certain medical conditions, such as diabetes.

A synergistic sweet effect can be achieved by blending Monellin with bulk and intense sweeteners, reducing the persistent sweetness and enhancing its overall taste profile. This property makes it a valuable addition to the development of various food products and sweeteners.

In summary, Monellin’s sweetness mechanism involves its interaction with the sweet taste receptors, particularly the T1R2-T1R3 complex, and its molecular structure, which plays a critical role in its sensory properties. The potential applications of Monellin in the food and sweetener industries makes it a fascinating area of study and development.

Comparison with Other Sweet Proteins

Monellin is a sweet protein extracted from the fruit of the African serendipity berry, known for its characteristics of slow sweetness onset and lingering aftertaste. It shares many similarities with other sweet proteins, yet exhibits unique qualities that differentiate it from its counterparts.

Thaumatin is another sweet protein, derived from the katemfe fruit found in West Africa. Like monellin, thaumatin is much sweeter than sugar, around 1,600 to 3,200 times sweeter than sucrose. Thaumatin shares a pH-dependence feature with monellin, but it is relatively more stable in a wider pH range.

Miraculin and curculin are sweet taste-modifying proteins rather than purely sweet proteins. Both are found in tropical plants and have the unique ability to turn the taste of sour substances sweet. Miraculin is obtained from the miracle berry and is pH-dependent, while curculin comes from a plant native to Malaysia and exhibits more pronounced sweetness-enhancing properties. However, neither of these two proteins have the same degree of sweetness as monellin or thaumatin.

Brazzein, isolated from the African plant Pentadiplandra brazzeana, is another example of a sweet protein. Similar to monellin and thaumatin, brazzein has a high sweetness intensity, outpacing sucrose by a remarkable 2,000 times. Brazzein has good heat stability, making it a viable alternative to monellin in high-temperature applications.

Mabinlin is another sweet protein that has been discovered in the Chinese plant Capparis masaikai. Like monellin, mabinlin has a slow onset of sweetness and lingering aftertaste, yet exhibits heat stability superior to both monellin and thaumatin.

Neoculin is an unusual sweet protein derived from the fruit of the miracle plant Dioscoreophyllum cumminsii. This protein differs from other sweet proteins due to its ability to produce a sweet taste followed by a cooling sensation in the mouth.

Pentadin and gurmarin are additional examples of sweet proteins, though their profiles and characteristics have not been as widely researched as the aforementioned proteins. Pentadin is derived from the African plant Oubli, while gurmarin is obtained from the leaves of Gymnema sylvestre.

In summary, while monellin shares various features and characteristics with other sweet proteins like thaumatin, brazzein, and mabinlin, it exhibits particular qualities that set it apart. The pH-dependence, slow sweetness onset, and lingering aftertaste are key aspects of monellin that differentiate it from many other sweet proteins.

Potential Applications

As a Sweetener

Monellin, a sweet protein isolated from the fruit of Dioscoreophyllum cumminsii (also known as the serendipity berry), is native to West Africa. It has the potential to serve as an alternative to sugar-based sweeteners. Due to its high sweetness, only a small amount of Monellin is needed to achieve a sweet taste, which could benefit individuals looking for low-calorie options.

In Food Industry

Monellin could be an attractive option for the food industry, as it offers a natural sweetener without the aftertaste sometimes associated with artificial sweeteners. However, one of the challenges in using Monellin as a food additive is its low heat and acid resistance. When exposed to temperatures above 50°C, it loses its sweetness. To overcome this limitation, researchers have engineered new heat-stable forms of Monellin by connecting its two chains.

For Diabetics

Since Monellin is a protein-based sweetener and not a carbohydrate, it has potential benefits for diabetics. It can help them manage their blood sugar levels more effectively than traditional sucrose or other processed sweeteners. However, further research and regulatory approvals may be required before widespread use in products targeting diabetics.

Currently, Monellin’s legal status as a food additive may vary across different regions, such as the European Union and the United States. As its potential applications continue to be explored, the availability, use, and acceptance of Monellin as a viable alternative to sugar may increase over time.

Production and Modifications

Expression in Yeast and Micro-organisms

Monellin is a sweet protein that can be expressed in yeast and other micro-organisms for large-scale production. For instance, the yeast Pichia pastoris has been used to enhance Monellin production by regulating methanol metabolism patterns and energy utilization efficiency 1. This approach allows for high yields of the protein while maintaining its sweetness properties and functionality.

Chemical Synthesis

Chemical synthesis of Monellin can be accomplished using solid-phase peptide synthesis methods. This method typically involves the assembly of amino acid residues in a stepwise manner, forming the final protein structure. This approach allows for precise control over the protein sequence, enabling the introduction of desired modifications or mutations.


Mutations in the Monellin protein can lead to changes in its stability, sweetness, and overall properties. One notable example is MNEI, a single-chain variant of Monellin which has enhanced sweetness and stability compared to the original protein 2. However, MNEI’s use is limited due to its low stability and high aggregation propensity at neutral pH. To overcome these limitations, researchers have developed mutant Monellin proteins with improved characteristics, such as increased stability and reduced aggregation, while retaining sweetness 2.

Safety and Regulatory Status

Monellin is a sweet protein derived from the fruit of Dioscoreophyllum cumminsii, also known as the Serendipity Berry, which is native to West Africa. Due to its high sweetness levels, monellin has the potential to be used as a harmless additive in various food products, specifically for those following low-calorie or sugar-free diets.

Although monellin is generally considered safe for consumption, it is important to note that it has not been granted legal status by the Food and Drug Administration (FDA) in the United States or the European Food Safety Authority (EFSA). This implies that further research and evaluation are necessary to fully establish monellin’s safety profile and potential health risks.

That being said, monellin is significantly sweeter than sugar and requires only small amounts to achieve the desired sweetness level in food items. This property denotes that it has potential applications in food products intended for individuals with health concerns, such as diabetes, as it may not significantly impact insulin levels in comparison to traditional sugar.

In conclusion, while monellin’s potential as a safe and effective sugar replacement is evident, it is crucial to consider the current regulatory limitations and additional research required to establish this protein’s safety and possible health implications definitively.

Concluding Remarks

Monellin is a sweet protein that was first discovered in 1969 in the fruit of the West African shrub known as serendipity berry (Dioscoreophyllum cumminsii). This protein, which consists of two non-covalently associated polypeptide chains A and B, can be found in small amounts within the fruit and has a significantly high sweetness level.

Due to its high sweetness, monellin holds potential for use in creating low-calorie diet foods. However, it isn’t suitable for all food applications, as its sweetness quickly diminishes when exposed to heat, rendering it ineffective for baking purposes. In an attempt to overcome this issue, researchers have engineered heat-stable forms of monellin by connecting the two chains.

Though monellin is a naturally occurring sweet protein, its use in the food industry still presents challenges, given its heat sensitivity and the need for specific processing techniques to maintain its sweetness. Furthermore, it is worth mentioning that the sweet taste of monellin is only detectable by humans and old world monkeys.

In summary, monellin showcases an interesting and valuable property in its high sweetness level, offering potential benefits for low-calorie food solutions. While it is not without its limitations, ongoing research and development efforts may continue to unlock the full potential of this intriguing protein derived from the serendipity berry.

Frequently Asked Questions

What are the chemical constituents of Monellin?

Monellin is a sweet protein composed of two non-covalently linked polypeptide chains. It originally isolated from the fruit of Dioscoreophyllum cumminsii (Stapf) Diels, also known as the serendipity berry, native to West Africa.

How does Monellin compare to Thaumatin?

Thaumatin is another sweet protein derived from the African plant Thaumatococcus daniellii. Both Monellin and Thaumatin are intensely sweet proteins, yet they differ in their structures and properties. While Monellin is composed of two polypeptide chains, Thaumatin consists of a single polypeptide chain. Additionally, Thaumatin is approximately 100,000 times sweeter than sucrose, while Monellin is about 90,000 times sweeter on a molar basis.

What plant is Monellin derived from?

Monellin is derived from the fruit of Dioscoreophyllum cumminsii (Stapf) Diels, also known as the serendipity berry, which is native to West Africa.

What is the sweetness level of Monellin?

Monellin is an intensely sweet protein. It is about 90,000 times sweeter than sucrose (table sugar) on a molar basis. The sweetness is described as “intense and persistently sweet.”

Are there any similar sweet proteins to Monellin?

Yes, there are other sweet proteins, such as Thaumatin, which is derived from the African plant Thaumatococcus daniellii. Another example is Brazzein, obtained from the fruit of the West African plant Pentadiplandra brazzeana.

How is Monellin used commercially?

Due to its intense sweetness and low-calorie content, Monellin has potential applications in the food industry as a sugar substitute. It can be used in a variety of food products, such as beverages, confectionery, and baked goods, to provide a sweet taste without contributing significantly to the calorie content. However, the commercial use of Monellin is still limited compared to other alternative sweeteners, and ongoing research aims to improve its stability and production for broader applications.


  1. Enhancing Monellin production by Pichia pastoris at low cell induction concentration via effectively regulating methanol metabolism patterns and energy utilization efficiency, Luqiang Jia, Tingyong Tu, Qiangqiang Huai, Jiaowen Sun, Shanshan Chen, Xin Li, Zhongping Shi, Jian Ding.

  2. Single-chain Monellin, MNEI. 2