Title: Alternative Sweeteners

336 Olinger and Pepper
Table 1 Some Physical and Chemical Properties of Xylitol
Formula C 5H 12O 5 (molecular weight, 152.15)
Appearance White, crystalline powder
Odor None
Specific rotation Optically inactive
Melting range 92–96°C
Boiling point 216°C (760 mmHg)
Solubility at 20°C 169 g/100 g H 2O; 63 g/100 g solution; sparingly
soluble in ethanol and methanol
pH in water (100 g/liter) 5–7
Density of solution 10%, 1.03 g/ml; 60%, 1.23 g/ml
Viscosity (20°C) 10%, 1.23 cP; 60%, 20.63 cP
Heat of solution 34.8 cal/g (endothermic)
Heat of combustion 16.96 kJ/g
Refractive index (25°C) 10%, 1.3471; 50%, 1.4132
Moisture absorption (4 days, 60% RH, 0.051% H 2O, 92% RH, 90% H 2O
RT)
Relative sweetness Equal to sucrose; greater than sorbitol and
mannitol
Stability Stable at 120°C, no caramelization; stable
also under usual conditions in food
processing; carmelization occurs if heated
for several minutes near the boiling point
cP centipoise.
RH relative humidity.
RT room temperature.
by-products (e.g., poly- or oligosaccharides), which have to be removed during
the production process. In principle, the commercial synthesis of xylitol involves
four steps. The first step is the disintegration of natural xylan-rich material and
the hydrolysis of the recovered xylan to xylose. The second step is the isolation
of xylose from the hydrolysate by means of chromatographic processes to yield
a pure xylose solution. Third, xylose is hydrogenated to xylitol in the presence
of a nickel catalyst. Alternatively, hydrogenation of the impure xylose solution
may be conducted first, followed by purification of the xylitol syrup. Ultimately,
xylitol is crystallized in orthorhombic form (26).
The synthesis of xylitol by fermentativeor enzymatic processes is possible
in principle (27–30). However, such procedures have so far not been used on a
commercial scale. Other approaches to the synthesis of xylitol are of merely
scientific interest (31,32).
Xylitol is supplied commercially in crystalline, milled, and granulated
forms. Crystalline xylitol has a mean particle size of about 400 to 600 microns.