Title: Alternative Sweeteners

318 Le and Mulderrig
out and the solution is purified. It is then evaporated to 70% solids and sold as
sorbitol solution (1).
Crystalline sorbitol is made by further evaporating the sorbitol solution into
molten syrup containing at least 99% solids. The molten syrup is crystallized
into a stable crystalline polymorph that has one single melting point (99–101°C)
and heat of fusion (42 cal/g, assuming 44 cal/g represents a fully crystallized
crystalline sorbitol). The stable polymorph of sorbitol is known as gamma (γ)
sorbitol and was determined from the work of Atlas Powder Company and University
of Pittsburgh researchers in the early 1960s. Most commercially available
crystalline sorbitol is the gamma polymorph (2, 3).
When hydrogenated invert sugar is the raw material, both sorbitol and mannitol
are produced in the solution because they are isomers. The mannitol and
sorbitol are separated on the basis of their different solubilities. Mannitol is crystallized
from the solution because of its lower solubility than sorbitol in water.
The resulting product is the most stable polymorph, the β-polymorph (4). Mannitol
is then filtered, dried, and sold as white powder or free-flowing granules (directly
compressible material).
III. PHYSICAL AND CHEMICAL PROPERTIES OF
SORBITOL AND MANNITOL
Sorbitol and mannitol are six-carbon, straight-chain polyhydric alcohols, meaning
they have more than one hydroxyl group. Both sorbitol and mannitol have six
hydroxyl groups and the same molecular formula, C 6H 14O 6. They are isomers of
one another and have different molecular configurations. The difference between
sorbitol and mannitol occurs in the planar orientation of the hydroxyl group on
the second carbon atom (Figs. 1 and 2). This dissimilarity has a powerful influence
and results in an individual set of properties for each isomer.
Figure 1 The chemical structures of sorbitol and mannitol.