Brazzein is a sweet-tasting

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

extracted from the

West African West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, ...

fruit of the climbing plant

Oubli ''Pentadiplandra brazzeana'' is an evergreen shrub or liana that is the only species assigned to the genus ''Pentadiplandra'', and has been placed in a family of its own called Pentadiplandraceae. It produces large red berries, sometimes mottled ...

(''

Pentadiplandra brazzeana ''Pentadiplandra brazzeana'' is an evergreen shrub or liana that is the only species assigned to the genus ''Pentadiplandra'', and has been placed in a family of its own called Pentadiplandraceae. It produces large red berries, sometimes mottled ...

'' Baillon). It was first isolated by the

University of Wisconsin–Madison A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United Stat ...

in 1994. Brazzein is found in the extracellular region, in the pulp tissue surrounding the seeds. With

pentadin Pentadin, a sweet-tasting protein, was discovered and isolated in 1989, in the fruit of Oubli ('' Pentadiplandra brazzeana'' ), a climbing shrub growing in some tropical countries of Africa. The fruit has been consumed by the apes and the native ...

, discovered in 1989, brazzein is the second sweet-tasting protein discovered in the Oubli fruit. Like the other sweet proteins discovered in plants, such as monellin and thaumatin, it is extremely sweet compared to commonly used sweeteners (500 to 2000 times sweeter than

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refine ...

). The fruit tastes sweet to humans, monkeys, and bonobos, but

gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...

s have mutations in their sweetness receptors so that they do not find brazzein sweet, and they are not known to eat the fruit.

Traditional use

The Oubli plant (from which the protein was isolated) grows in

Gabon Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the nort ...

and

Cameroon Cameroon (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west-central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; the ...

, where its fruit has been consumed by the apes and local people for a long time. Due to brazzein and pentadin, the berries of the plant are incredibly sweet. African locals call them "Oubli" (French for "forgot") in their vernacular language because their taste is said to encourage nursing infants to forget their mother's milk, as once they eat them they are said to forget to come back to the village to see their mother.

Protein structure

The monomer protein, consisting of 54 amino acid residues, is the smallest of the sweet proteins with a molecular weight of 6.5 kDa. The

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

sequence of brazzein, adapted from the Swiss-Prot biological database of protein, is as follows: UniProtKB/Swiss-Prot database entry #PP56552
/ref>'' The structure of brazzein was determined by proton

nuclear magnetic resonance Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a ...

(NMR) at a pH of 5.2 and 22 °C. Brazzein has four evenly spaced disulfide bonds and no sulfhydryl groups. 3D analysis of brazzein showed one

alpha-helix The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand- helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ...

and three strands of anti-parallel

beta sheet The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a ge ...

. This is not superficially similar to either of the other two sweet-tasting proteins, monellin and thaumatin. However, a recent 3D study shows that these three proteins possess similar "sweet fingers" believed to elicit the sweet taste. Residues 29–33 and 39–43, plus residue 36, as well as the C-terminus were found to be involved in the sweet taste of the protein. The charge of the protein also plays an important role in its interaction with the sweet

taste receptor A taste receptor or tastant is a type of cellular receptor which facilitates the sensation of taste. When food or other substances enter the mouth, molecules interact with saliva and are bound to taste receptors in the oral cavity and other loc ...

. Based on this knowledge a synthesised improved brazzein, called pGlu-1-brazzein, was reported to be twice as sweet as the natural counterpart.

Sweetness properties

On a weight basis, brazzein is 500 to 2000 times sweeter than sucrose, compared to 10% sucrose and 2% sucrose solution respectively. Its sweet perception is more similar to sucrose than that of thaumatin, with a clean sweet taste, lingering aftertaste, and slight delay (longer than aspartame) in an equi-sweet solution. Brazzein is stable over a broad pH range from 2.5 to 8 and heat stable at 98°C for 2 hours.

As a sweetener

Brazzein represents an alternative to available low-calorie sweeteners. As a protein, it is safe for diabetics. It is also very soluble in water (>50 mg/mL). When blended with other sweeteners, such as

aspartame Aspartame is an artificial non- saccharide sweetener 200 times sweeter than sucrose and is commonly used as a sugar substitute in foods and beverages. It is a methyl ester of the aspartic acid/phenylalanine dipeptide with the trade na ...

and

stevia Stevia () is a natural sweetener and sugar substitute derived from the leaves of the plant species ''Stevia rebaudiana'', native to Paraguay and Brazil. The active compounds are steviol glycosides (mainly stevioside and rebaudioside), which ...

, brazzein reduces side aftertaste and complements their flavor. Its taste profile is closer to sucrose than other natural sweeteners (apart from thaumatin). Unlike other sweet-tasting proteins, it can withstand heat, making it more suitable for industrial food processing. Papers have been published showing it can be made in a laboratory using peptide synthesis and recombinant proteins were successfully produced via E. coli. The Texas companies Prodigene and Nectar Worldwide were among the licensees to use Wisconsin Alumni Research Foundation patents on brazzein, and genetically engineer it into maize. Brazzein then can be commercially extracted from the maize through ordinary milling. Approximately one ton of maize yields 1-2 kilograms of brazzein. It can also be engineered into plants like wheat to make pre-sweetened grains, e.g. for cereals. A company was formed to bring it to market as a sweetener in 2008, which initially said it would start selling the product by 2010 once it obtained agreement from the FDA that its brazzein was generally recognized as safe (GRAS). In 2012 the company said that regulatory approval might take an additional one or two years and in 2014 it still had not obtained a GRAS waiver from the FDA and was seeking partners, and the product was still not on the market as of 2016.

References

External links