Sugar Alcohols (Polyols) - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 60

Nephrotoxins and prolonged renal ischemia can damage renal tubules so that they become per-
meable to mannitol and its osmotic effect is lost. Finally, venous thrombosis is a rare event, and
tissue necrosis is unlikely with extravasation of mannitol (the opposite is true for urea). Mannitol
also increases plasma osmolarity and draws luid from intracellular to extracellular spaces reliev-
ing increased intracranial pressure (ICP) and increased ocular pressure. If the BBB is damaged,
worsened elevations in ICP could occur as mannitol enters the brain tissue and causes an osmotic
gradient into the tissue (Cosolo et al. 1989).
On the other hand, because it is slowly absorbed, excessive consumption may have a laxa-
tive effect, similar to certain high-iber foods. Because of this, products containing mannitol must
include a laxative warning on the label if the mannitol content in a serving exceeds 20 g. FDA
allows the use of a caloric value of 1.6 cal/g. It is permitted for use in many countries, including the
United States (Calorie Control Council 2011).
Mannitol does not promote tooth decay. It is approximately 72% as sweet as sugar (sucrose) and
is reported to have a cool, sweet taste (Sicard and Leroy 1983). Mannitol is widely used in the food
and pharmaceutical industries because of its unique functional properties. It is about 50% as sweet
as sucrose and has a desirable cooling effect often used to mask bitter tastes. Mannitol is noncario-
genic and has a low caloric content. It is suitable for ingestion and has been used safely around the
world for over 60 years (Sicard and Leroy 1983; Schiweck et al. 2011).
Production of mannitol by extraction of plant raw materials is no longer economically impor-
tant. Only in China mannitol is still obtained by acid extraction of marine algae. Mannitol can be
obtained from different sources; microbial formation of d-mannitol occurs with fungi (Vega and
Tourneau 1971) or bacteria (Foster 1949), starting with glucose, fructose, sucrose, or the tubers of
Jerusalem artichokes (Schlubach 1953). The precursor of mannitol in its biosynthesis in the mushroom
Agaricus bisporus is fructose. Mannitol is produced from glucose in 44% yield after six days by aero-
bic fermentation with Aspergillus candidus (Smiley et al. 1967) and in 30% yield after 10 days with
Torulopsis mannitofaciens (Onishi 1971). It is formed by submerged culture fermentation of fructose
with Penicillium chrysogenumin 7.3% conversion (Abdel-Akher et al. 1967). Small quantities of man-
nitol are found in wine (Barker et al. 1958). Today, mannitol is usually produced industrially (Figure
3.9) from sucrose, after inversion to glucose-fructose syrup (ratio 1:1), or from a glucose solution,
which is also converted to high-fructose corn syrup. Theoretically, 25% mannitol and 75% sorbitol are
formed in the neutral pH range from a 1:1 d-glucose-d-fructose syrup. Hydrogenation occurs under
high pressure in the presence of Raney nickel catalysts. As a result of its lower solubility compared
to sorbitol, mannitol is isolated from the concentrated hydrogenation solution by crystallization. The
iltrate still contains considerable amounts of mannitol, which can be separated chromatographically
(Oy 1973). If sucrose is used as starting material and hydrogenation is performed in alkaline solution,
mannitol yields of up to 31% can be obtained. In a pure glucose solution, moreover, d-glucose can be
epimerized to d-mannose before hydrogenation by the addition of an acidic solution of ammonium
molybdate. Mannose is then hydrogenated directly to d-mannitol (Schiweck et al. 2011).
Pure d-mannose is not yet commercially available, but it can be obtained by acid hydrolysis of
the mannan of ivory nutmeal in 35% yield and from spent sulite liquor or prehydrolysis extracts
from conifers through the sodium bisulite mannose adduct or methyl α-d-mannoside. Reduction
of fructose leads to sorbitol and d-mannitol in equal parts. Sucrose, on reduction under hydrolyzing
conditions, also yields the same products in the ratio of three parts of sorbitol to one of d-mannitol.
Commercially, d-mannitol is obtained by the reduction of invert sugar. In alkaline media, glu-
cose, fructose, and mannose are interconverted (Lobry de Bruyn and Alberda van Ekenstein 1895;
Wolfrom and Lewis 1928).
l-Mannitol does not occur naturally; however, it is obtained by the reduction of l-mannose or
l-mannonic acid lactone (Baer and Fischer 1939). It can be synthesized from the relatively abundant
l-arabinose through the l-mannose and l-glucose cyanohydrins, conversion to the phenylhydra-
zines that are separated, liberation of l-mannose, and reduction with sodium borohydride. Another