Monellin, a sweet protein, was discovered in 1969 in the fruit of the West African shrub known as serendipity berry (Dioscoreophyllum cumminsii); it was first reported as a carbohydrate. The protein was named in 1972 after the Monell Chemical Senses Center in Philadelphia, U.S.A., where it was isolated and characterized.

Protein composition

Monellin's molecular weight is 10.7 kDa. It has two noncovalently associated polypeptide chains: an A chain sequence with 44 amino acid residues, and a B chain with 50 residues.

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Monellin chain A (44 AA): <br />

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Monellin chain B (50 AA): <br />

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Amino acid sequence of the sweet protein monellin adapted from Swiss-Prot biological database of protein.</blockquote>

Monellin has a secondary structure consisting of five beta-strands that form an antiparallel beta-sheet and a 17-residue alpha-helix.

and 800 times sweeter than sucrose when compared with a 5% sucrose solution on a weight basis.

Monellin has a slow onset of sweetness and lingering aftertaste. Like miraculin, monellin's sweetness is pH-dependent; the protein is tasteless below pH 2 and above pH 9. Blending the sweet protein with bulk and/or intense sweeteners reduces the persistent sweetness and shows a synergistic sweet effect.<br /> Heat over 50&nbsp;°C at low pH denatures monellin proteins, causing a loss of the sweetness.

As a sweetener

Monellin can be useful for sweetening some foods and drinks, as it is a protein readily soluble in water due to its hydrophilic properties. However, it may have limited application because it denatures under high temperature conditions, which makes it unsuitable for processed food. It may be relevant as noncarbohydrate tabletop sweetener, especially for individuals such as diabetics who must control their sugar intake. and synthesised by solid-phase method. The synthetic monellin produce by yeast was found to be 4000 times sweeter than sucrose when compared to 0.6% sugar solution.<br />

Legal issues are the main barrier in its widespread use as a sweetener, as monellin has no legal status in the European Union or the United States. However, it is approved in Japan as a harmless additive, according to the List of Existing Food Additives issued by the Ministry of Health and Welfare (published in English by JETRO).

See also

  • Curculin
  • Thaumatin
  • Miraculin
  • Stevia

References

  • Monellin, PDB Molecule of the Month