D-Psicose

D-Psicose, also widely known as D-allulose, is a natural but rare monosaccharide. It is a ketohexose that has the same empirical formula as common monosaccharides such as glucose and fructose. It is epimeric with fructose at the 3-position. Its enantiomer, L-psicose¹, is unknown in nature but has been synthesized.

Known as early as 1915 as D-pseudofructose, German chemists H. Ohle and F. Just determined its structure in 1935 and renamed it D-psicose. In 1942, F. W. Zerban at the New York Sugar Trade Laboratory (New York City) and Louis Sattler at Brooklyn College (NY) isolated it from commercial cane molasses. At the time, it was deemed to be unfermentable and therefore of little practical value.

The physical state of D-psicose is variously reported in the literature as a viscous liquid or a white crystalline solid with a melting point of 58 °C or 109 °C. These discrepancies are probably attributable to the difficulty of crystallizing the compound. At ≈1.0 kg/L, it is extremely soluble in water. (Glucose dissolves at ≈900 g/L, fructose at ≈4 kg/L.)

D-Psicose is 70% as sweet as sucrose (table sugar), but it has only ≈10% of the nutritional energy (calorie) value. As a result, it is under development as a replacement for sucrose and artificial sweeteners. It was originally produced from corn; but this year, food-ingredient startup Bonumose (Charlottesville, VA) and drug-services company Novasep (Lyon, France) teamed up to manufacture D-psicose and fellow low-calorie sugar D-tagatose² from cellulose, starch, or their derivatives via an enzymatic process.

1. CAS Registry No. 16354-64-6.
2. CAS Registry No. 87-81-0.