Title: Alternative Sweeteners

Trehalose 425
Figure 1 Structure of α,α-trehalose dihydrate.
sugar consisting of two glucose molecules bound by an α,α 1,1 glycosidic linkage
(Fig. 1). After ethanol extraction or enzymatic synthesis, trehalose crystallizes
to a stable dihydrate form (1, 5). Trehalose can also be found in nature as α,β
(neotrehalose) and β,β (isotrehalose) isomers; however, these are uncommon,
and they possess chemical and physical properties that are distinct from α,αtrehalose.
In this review ‘‘trehalose’’ will be used to designate the α,α-trehalose
form. The chemical formula and molecular weight of trehalose dihydrate are
C 12H 22O 11 ⋅ 2H 2O and 378.33. The Chemical Abstracts Service Registry Number
is 6138-23-4.
V. PHYSICAL PROPERTIES
Physical properties reported in this section are, in large part, obtained from assays
of trehalose produced enzymatically from starch by Hayashibara Company Ltd.
(HBC) of Okayama, Japan; however, data from other sources are included (5).
Trehalose is available as a white crystalline powder that is colorless and
of prismatic rhomboid form. X-ray diffraction reveals cell parameters of a
12.33, b 17.89, and c 7.66 A (11, 12). The orthorhombic cell formula is
given as P2 12 12 1, and the units per cell are 4. The theoretical density of 1.511 g/
cm 3 agrees closely with the actual value of 1.512 g/cm 3 . Reports of the melting
point of trehalose dihydrate range from 94–100°C (1). Continued heating above
100°C vaporizes the water of hydration, resulting in resolidification; a second
melting point is reached at 205°C (1). The melting point of trehalose dihydrate
produced and assayed by HBC (97°C) equals the value listed in reference texts
(13, HBC, unpublished data, 1997). The melting point of Hayashibara anhydrous
trehalose is 210.5°C, approximately 7.5°C higher than reported in the literature
(13, HBC, unpublished data, 1997).
Birch reports data from several studies in which the optical rotation of
various preparations of trehalose ranged from 177° to 197.14°, but gives a
value of 199° for his own anhydrous preparation (1, 14). Unpublished data