2009_Book_FoodChemistry

432 8 Food Additives
intensive α-keto enamine (Formula 8.2) having
a threshold of 0.24 µmol/l, which is 38 times
lower than that of menthol.
8.7 Sugar Substitutes
(8.2)
Sugar substitutes are those compounds that are
used like sugars (sucrose, glucose) for sweetening,
but are metabolized without the influence of
insulin. Important sugar substitutes are the sugar
alcohols, sorbitol, xylitol and mannitol and, to
a certain extent, fructose (cf. 19.1.4.5–19.1.4.7).
8.8 Sweeteners
Sweeteners are natural or synthetic compounds
which imprint a sweet sensation and possess no or
negligible nutritional value (“nonnutritive sweeteners”)
in relation to the extent of sweetness.
There is considerable interest in new sweeteners.
The rise in obesity in industrialized countries has
established a trend for calorie-reduced nutrition.
Also, there is an increased discussion about the
safety of saccharin and cyclamate, the two sweeteners
which were predominant for a long time.
The search for new sweeteners is complicated
by the fact that the relationship between chemical
structure and sweetness perception is not yet
satisfactorily resolved. In addition, the safety of
suitable compounds has to be certain. Some other
criteria must also be met, for example, the compound
must be adequately soluble and stable over
a wide pH and temperature range, have a clean
sweet taste without side or post-flavor effects, and
provide a sweetening effect as cost-effectively as
does sucrose. At present, some new sweeteners
are on the market (e. g., acesulfame and aspartame).
The application of a number of other compounds
will be discussed here.
The following sections describe several sweeteners,
irrespective of whether they are approved,
banned or are just being considered for future
commercial use.
8.8.1 Sweet Taste: Structural Requirements
8.8.1.1 Structure–Activity Relationships
in Sweet Compounds
A sweet taste can be derived from compounds
with very different chemical structures.
Shallenberger and Acree consider that for
sweetness, a compound must contain a proton
donor/acceptor system (AH s /B s -system), which
has to meet some steric requirements and which
can interact with a complementary receptor
system (AH r /B r -system) by involvement of two
hydrogen bridges (Fig. 8.2). The expanded model
of Kier has an additional hydrophobic interaction
with a group, X, present at a distinct position of
the molecule (Fig. 8.3). The examples in Figs. 8.2
and 8.3 show that these models are applicable
to many sweet compounds from highly different
classes. An enlarged model substitutes a nucleophilic/electrophilic
system (n s /e s system) for the
AH s /B s system and an extended hydrophobic
contact for the localized contact with group X.
Fig. 8.2. AH/B-systems of various sweet compounds