2009_Book_FoodChemistry

866 19 Sugars, Sugar Alcohols and Honey
Fig. 19.4. Sorption of water by sugars at room temperature.
1 Saccharose, 2 xylitol, 3 fructose, 4 sorbitol (according
to Koivistoinen, 1980)
Creams and gels with the same amounts of sweetener
are often less sweet than the corresponding
aqueous solutions. The sweet taste intensity
may also depend on temperature (Fig. 19.5),
Fig. 19.6. Fructose mutarotation equilibrium as affected
by temperature (according to Shallenberger,
1975)
an effect which is particularly pronounced with
fructose – hot fructose solutions are less sweet
than cold ones. The cause of such effects is the
mass equilibrium of sugar isomers in solution.
At higher temperatures the concentration of the
very sweet β-D-fructopyranose drops in favor
of both the less sweet α-D-fructofuranose and
the β-D-fructofuranose (Fig. 19.6). Such strong
shifts in isomer concentrations do not occur
with glucose, hence its sweet taste intensity is
relatively unchanged in the range of 5–50 ◦ C.
19.1.3 Nutritional/Physiological Properties
19.1.3.1 Metabolism
Fig. 19.5. Sugar sweetness intensity versus temperature.
At all temperatures the saccharose taste intensity
is 100 (according to Shallenberger, 1975)
The role of carbohydrates in metabolism is primarily
determined by the ability of disaccharides
to be hydrolyzed in the gastrointestinal tract and
by the mechanisms of monosaccharide absorption.
The human organism hydrolyzes sucrose, lactose
and oligosaccharides of the maltose and
isomaltose type. The enzyme lactase, which is
responsible for lactose hydrolysis, is lacking in
some adults. Glucose and galactose are actively
transported, while all other monosaccharides are
transported only by diffusion. Sugar phospho-