Food Chemistry

4.2 Monosaccharides 261

Fig. 4.9.Bitter taste threshold values of limonin(◦—◦)
and naringin (× 10 −^1 • —•) in aqueous saccharose solu-
tion (according toGuadagni, 1973)

forβ-D-glucopyranose andβ-D-fructopyranose
respectively:

(4.23)

β-D-glucopyranose and β-L-glucopyranose are
sweet. Molecular models show that the AH/B/X-
system of both sugar components fits equally
well with the complementary receptor system
AHR/BR/XR(Formula 4.24):

(4.24)

With asparagine enantiomers, the D-form is
sweet, while theL-form is tasteless. Here, unlike
D-andL-glucose, only theD-form interacts with
the complementary AHR/BR/XR-system:

(4.25)

As described in 8.8.1.1, the AH/B/X-system has

been extended to explain the large differences in

structure and sweetening strength which can exist

in compounds of different substance classes.

4.2.4 ChemicalReactionsandDerivatives........................

4.2.4.1 Reduction to Sugar Alcohols

Monosaccharides can be reduced to the corres-

ponding alcohols by NaBH 4 , electrolytically or

via catalytic hydrogenation. Two new alcohols

are obtained from ketoses, e. g., fructose, since

a new chiral center is formed:

(4.26)

The alcohol name is derived from the sugar name

in each case by replacing the suffix -ose or -ulose

with the suffix -itol. The sugar alcohols of import-

ance in food processing are xylitol, the only one

of the four pentitols (mesoribitol,D,L-arabitol,

mesoxylitol) used, and onlyD-glucitol (sorbitol)

andD-mannitol of the ten stereoisomeric forms of

hexitols [meso-allitol, meso-galactitol (dulcitol),

D,L-glucitol (sorbitol),D,L-iditol,D,L-mannitol

andD,L-altritol]. They are used as sugar substi-

tutes in dietetic food formulations to decrease wa-

ter activity in “intermediate moisture foods”, as

softeners, as crystallization inhibitors and for im-

proving the rehydration characteristics of dehy-

drated food. Sorbitol is found in nature in many

fruits, e. g., pears, apples and plums. Palatinitol

(a mixture of glucopyranosyl glucitol and glu-