2009_Book_FoodChemistry

19 Sugars, Sugar Alcohols and Honey
19.1 Sugars, Sugar Alcohols
and Sugar Products
19.1.1 Foreword
Only a few of the sugars occurring in nature
are used extensively as sweeteners. Besides
sucrose (saccharose), other important sugars
are: glucose (starch sugar or starch syrup);
invert sugar (equimolar mixture of glucose and
fructose); maltose; lactose; and fructose. In
addition, some other sugars and sugar alcohols
(polyhydric alcohols) are used in diets or for
some technical purposes. These include sorbitol,
xylitol, mannitol, maltulose, isomaltulose,
maltitol, isomaltitol, lactulose and lactitol. Some
are used commonly in food and pharmaceutical
industries, while applications for others are
being developed. Food-grade oligosaccharides,
which can be economically produced, are physiologically
and technologically interesting. This
group includes galacto-, fructo-, malto- and
isomalto-oligosaccharides. Table 19.1 reviews
relative sweetness, source and means of production,
and Table 19.2 gives nutritional and
physiological properties. Whether compounds
will be successful as a sweetener depends on nutritional,
physiological and processing properties,
cariogenicity as compared to sucrose, economic
impact, and the quality and intensity of the sweet
taste.
19.1.2 Processing Properties
The potential of a compound for use as a sweetener
depends upon its physical, processing and
sensory properties. Important physical properties
are solubility, viscosity of the solutions, and hygroscopicity.
Figure 19.1 shows that the solubility
of sugars and their alcohols in water is variable
and affected to a great extent by temperature.
Fig. 19.1. Solubility of sugars and sugar alcohols in water
(according to Koivistoinen, 1980)
There are similar temperature and concentration
influences on the viscosity of aqueous solutions
of many sugars and sugar alcohols. As an example,
Fig. 19.2 shows viscosity curves for sucrose
as a function of both temperature and concentration.
The viscosity of glucose syrup depends on its
composition. It increases as the proportion of the
high molecular weight carbohydrates increases
(Fig. 19.3).
Figure 19.4 shows the water absorption characteristics
of several sweeteners. Sorbitol and
fructose are very hygroscopic, while other sugars
absorb water only at higher relative humidities.
Chemical reactions of sugars were covered
in detail in Chapter 4. Only those reactions
important from a technological viewpoint will be
emphasized here.
All sugars with free reducing groups are very reactive.
In mildly acidic solutions monosaccharides
are stable, while disaccharides hydrolyze
to yield monosaccharides. Fructose is maximally
stable at pH 3.3; glucose at pH 4.0. At lower
pH’s dehydration reactions prevail, while the Lobry
de Bruyn–van Ekenstein rearrangement oc-
H.-D. Belitz · W. Grosch · P. Schieberle, Food Chemistry 862
© Springer 2009