Food Chemistry

866 19 Sugars, Sugar Alcohols and Honey

Fig. 19.4.Sorption of water by sugars at room temper-
ature. 1 Saccharose, 2 xylitol, 3 fructose, 4 sorbitol (ac-
cording toKoivistoinen, 1980)

Creams and gels with the same amounts of sweet-
ener are often less sweet than the corresponding
aqueous solutions. The sweet taste intensity
may also depend on temperature (Fig. 19.5),

Fig. 19.5.Sugar sweetness intensity versus tempera-
ture. At all temperatures the saccharose taste intensity
is 100 (according toShallenberger, 1975)

Fig. 19.6.Fructose mutarotation equilibrium as af-

fected by temperature (according toShallenberger,

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 sweetβ-D-fructopyranose drops in favor

of both the less sweetα-D-fructofuranose and

theβ-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

The role of carbohydrates in metabolism is pri-

marily determined by the ability of disaccharides

to be hydrolyzed in the gastrointestinal tract and

by the mechanisms of monosaccharide absorp-

tion.

The human organism hydrolyzes sucrose, lac-

tose 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-