Title: Alternative Sweeteners

Tagatose 107
the same type of Food and Drug Administration (FDA)–approved calcium-based
cationic resins. The galactose fraction from chromatography is converted to dtagatose
under alkaline conditions by adding a suspension of technical-grade
Ca(OH)2 and, optionally, a technical-grade catalyst, CaCl2. The reaction is
stopped by adding technical-grade sulfuric acid (H 2SO 4). A limited number of
side reactions are observed as part of the isomerization process of d-galactose.
The reactions are well known and are typical of those that occur between all
common hexose monosaccharides (like d-fructose and d-glucose) and any source
of hydroxide ion. Tagatose is stable under the conditions of the isomerization
process.
On removal of the gypsum formed, the resulting filtrate is further purified
by means of demineralization and chromatography. The purified d-tagatose solution
is then concentrated and crystallized to give a white crystalline product
(99% pure) (Fig. 2).
III. GASTROINTESTINAL FATE OF D-TAGATOSE
The rather small difference in chemical structure of d-tagatose compared with
fructose has large implications on the overall metabolism of the sugars. The fructose
carrier-mediated transport in the small intestine has no affinity for d-tagatose,
and only approximately 20% of ingested d-tagatose is absorbed in the small
intestine. The absorbed part is metabolized in the liver by the same pathway
as fructose. The major part of ingested d-tagatose is fermented in the colon by
indigenous microflora, resulting in the production of short-chain fatty acids
(SCFAs).
A. Absorption in the Small Intestine
Among the different dietary monosaccharides, glucose and galactose are absorbed
by an active energy-consuming transport mechanism. Fructose and xylose
are absorbed by carrier-mediated, so-called facilitated diffusion. All other sugars
are absorbed by passive absorption. Although d-tagatose and d-fructose are similar
in terms of molecular structure, they are not taken up in the small intestine
by the same carrier mechanism. In vitro experiments showed that d-tagatose does
not inhibit the absorption of fructose or glucose (at concentrations up to 100
times greater than those of fructose) (3, 4). Binding of d-tagatose to the glucose
and fructose carriers followed by transport across the mucosa can, therefore, be
excluded.
The estimated absorption of radio labeled d-tagatose in rats is approximately
20% (5). Similarly, less than 26% of ingested d-tagatose was absorbed