Monellin is a sweet protein extracted from the fruit of the plant Dioscoreophyllum cumminsii (Stapf) Diels. The plant is grown widely throughout West Africa where it is known as the Serendipity Berry.
It was identified and extracted in 1972 (Morris and Cagan, 1972).
Structure
A basic protein with an isoelectric point of approximately 9.3. The molecular mass is 10.7 kDa. Monellin has two noncovalently associated polypeptide chains: chain A contains 44 amino acid residues and chain B has 50 residues. The crystal structure has been established (Wlodawer and Hodgson, 1975).
The protein is related to thiol proteinase inhibitors known as cystatins which indicates it has a defence purpose in the plant (Murzin, 1993).
No carbohydrate moieties are attached.
Sweetness
Monellin is 3,000 times sweeter than sucrose. On a molar basis, it is estimated that the flavour is approximately 100,000 times sweeter than sugar on a molar basis. The sweetness perception lasts for over an hour with a lingering aftertaste which is often the situation with protein sweeteners such as thaumatin and brazzein. It shows synergies in sweetness with luo han guo (monk fruit), stevioside and rebaudioside.
Stability
It is not stable to heat. The instability is a limitation in product development because it is not useful for baked goods.
References
Morris, J. A., & Cagan, R. H. (1972). Purification of monellin, the sweet principle of Dioscoreophyllum cumminsii. Biochimica et Biophysica Acta (BBA)-General Subjects, 261(1), pp. 114-122. https://doi.org/10.1016/0304-4165(72)90320-0
Murzin, A. G. (1993). Sweet-tasting protein monellin is related to the cystatin family of thiol proteinase inhibitors. Journal of Molecular Biology, 230(2), pp. 689-694. https://www.sciencedirect.com/science/article/pii/S0022283683711861
Wlodawer, A., & Hodgson, K. O. (1975). Crystallization and crystal data of monellin. Proceedings of the National Academy of Sciences, 72(1), pp. 398-399. http://www.pnas.org/content/72/1/398.short
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