Title: Alternative Sweeteners

434 Richards and Dexter
Table 3 Comparison of the Osmotic Pressure of
Concentrations of Trehalose and Maltose
Concentration of sugar (% w/w)
Sugar 5 10 20 30
Trehalose 193 a 298 690 1229
Maltose 195 299 676 1221
a Osmotic pressure measured in milliosmoles.
(28, 29, 36, 44, 45). Proteins dried in the presence of trehalose are physically
constrained from undergoing degradative reactions (41). Several reports in the
literature have cited instances in which enzymes preserved in trehalose have remained
active, even after exposure and extended storage at high temperatures
(36).
A review of the literature suggests that there may be several important
reasons for the superiority of trehalose in preventing the destructive chemical
and physical reactions that accompany drying and freezing. Trehalose glasses are
purported to function by a number of mechanisms including the following:
1. Reduction in molecular mobility—The formation of a stable glass reduces
molecular mobility and prevents destructive physical forces, like fusion,
from taking place during freezing or drying.
2. Reduction in water activity—Water activity is necessary for degradative
interactions such as the Maillard reaction, which occurs between proteins
and other biocomponents (35). Trehalose glasses are hydrophilic and bind water
tightly if excess water is introduced into the system (42). Trehalose glasses are
almost unique in their ability to form a dihydrate compound, when excess water
is present, effectively lowering the water activity (43). Ding et al. stated that the
kinetics of most chemical reactions can be essentially shut down by the high
viscosity of vitreous trehalose glasses, even at temperatures well above the glass
transition temperature (42). They demonstrated that trehalose glasses can absorb
up to 0.15 moles of water per mole of trehalose without loss of rigidity at ambient
temperature (42). Others have reported that the freeze-drying of a 0.25 molar
(9.45%) trehalose solution did not remove all the water. After storing the preparation
for 48 hours under vacuum, the sample retained 0.02 g of water per gram
of trehalose (41). The glass transition temperature determined for this preparation
was 92°C. When the sample was stored at ambient temperature and high humidity
for 66 hours, it absorbed water vapor, and 70% of the sample reverted to trehalose
dihydrate (41).
3. Immobilization of active end-groups—Proteins are reported to contain
between 0.25–0.75 g of water per gram of protein (27). Phospholipids also reside