Title: Alternative Sweeteners

Crystalline Fructose 371
Table 3 Fructose Contents of Fruits
Percent Percent fructose in
Fruit fructose in fruit total solids
Apple 6.04 37.8
Blackberry 2.15 14.1
Blueberry 3.82 24.0
Currant 3.68 20.8
Gooseberry 3.90 26.3
Grape 7.84 41.0
Pear 6.77 49.9
Raspberry 4.84 17.2
Sweet cherry 7.38 32.9
Strawberry 2.40 25.4
these unique differences. ‘‘Practical Applications of Crystalline Fructose,’’ found
later in this chapter, illustrates ways in which these properties may be used to
advantage in food products.
A. Relative Sweetness
The functional property that most distinguishes fructose from other nutritive carbohydrates
is its high relative sweetness. Relative sweetness is a subjective comparison
of the peak organoleptic perception of sweetness of a substance, usually
in relation to a sucrose reference. Reported relative sweetness values fall in the
range of 1.8 times that of sucrose for crystalline fructose and 1.2 times that of
sucrose for liquid fructose (5). However, it must be emphasized that the relative
sweetness of fructose depends on the anomeric state of fructose at the time the
sweetness comparison is made.
Only the sweetest, β-d-fructopyranose, anomer exists in crystalline fructose.
Fructose rapidly mutarotates on dissolution in water, forming three additional
tautomers possessing lower sweetness (6). The extent of mutarotation can
be determined using optical rotation, gas-liquid chromatography, and nuclear
magnetic resonance (NMR). These techniques have been used to determine that
at 22°C the tautomeric equilibrium concentrations of 20% solids fructose in D 2O
are as illustrated in Fig. 1 (7).
Temperature, pH, concentration of the solution, and presence of other
sweeteners are factors that most influence sweetness intensity. Of these, only
temperature exerts a significant effect on the mutarotational behavior of fructose
in solution and on the transformation from the sweetest β-d-fructopyranose form
to an equilibrium state in which less sweet tautomeric forms are present (6, 8).