In Monellin, two peptide chains are linked together by non-covalent interactions forming a five-strand β-sheet half-wrapped around an α-helix ( Ogata et al., 1987).

It is a small globular protein (94 residues), composed of two polypeptide chains. Monellin is another intensely sweet protein, isolated from Dioscoreophyllum cumminsii, a West Africa tropical plant ( Inglett and May 1969). Thaumatin is very soluble in water, up to 600 mg/ml, and is endowed by high thermal stability under acidic conditions, with retained sweetness at 80☌ for several hours ( Kaneko and Kitabatake, 2001). Thaumatin is extracted from Thaumatococcus danielli, a West African plant, as a combination of two proteins: Thaumatin I and II ( van der Wel and Loeve, 1972). Among all sweet proteins, Thaumatin ( van der Wel and Loeve, 1972) and Monellin ( Morris and Cagan, 1972) are the sweetest, being approximately 100,000 times sweeter than sucrose, on molar basis ( Temussi, 2006b). Sweet proteins stand out not only because they have much larger molecular weight (and corresponding large volumes) with respect to all other sweeteners, but also, they are the sweetest known natural molecules up to date. Sweetness is elicited by a very large variety of molecules, both natural and synthetic ( Temussi, 2006a Temussi, 2007). This result is explained by the interference of ionic strength with the mechanism of action of sweet proteins and provides an experimental validation of the wedge model for the interaction of proteins with the sweet receptor.

Parallel tasting of small size sweeteners revealed no influence of the water quality.

During studies of sweet proteins as food additives we found that their sweetness is affected by water salinity, while there is no influence on protein’s structure. This aspect prompted several proposals for their use as food additives, mainly because the amounts to be added to food would be very small and safe for people suffering from sucrose-linked diseases. Sweet proteins are the sweetest natural molecules. 2UK Dementia Research Institute at King’s College London, The Maurice Wohl Institute, London, United Kingdom.1Department of Chemical Sciences, University of Naples “Federico II”, Complesso Universitario Monte S.Masoud Delfi 1 †, Alessandro Emendato 1 †, Piero Andrea Temussi 1,2* and Delia Picone 1*

Sweetness on the water