Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
HOH 2C-CH-CH-CH 2OH
HOH 2C-CH-CH-CH-CH 2OH
HOH 2C-CH-CH-CH-CH-CH 2OH
HOH 2C-CH-CH-CH-CH 2OH
OH OH
OH OH OH
3.1 3.2
OH
OH OH OH OH
3.2 3.4
OH
OH OH OH
HOH 2C-CH-CH-CH-CH-CH 2OH
HOH 2C-CH-CH-CH-CH-CH 2OH
β-D-Galp
1
↓
O
HOH 2C-CH-CH-CH-CH-CH 2OH
OH OH OH
α-D-Glcp
1
O ↓
OH OH
OH OH OH
3.5 3.6
An enzymatic redox system is believed to be responsible for the conversion of xylose
to xylitol in bacteria, fungi, and yeasts. 8
Because mannose is not available industrially, mannitol (3.4) is obtained from
hydrogenation of fructose, which is from either sucrose or starch. Sucrose, after
hydrolysis, can be hydrogenated to produce a mixture of sorbitol (3.5) and mannitol.
Dextrose from hydrolyzed starch can be isomerized to fructose, which is then
reduced to sorbitol and mannitol. Mannitol is isolated by fractional crystallization
due to its lower solubility in water compared with sorbitol, but the yield does not
exceed 15 to 18%. 9
Sorbitol is a reduced form of dextrose and the most available polyol. Sorbitol
can be produced from electrochemical reduction of dextrose in an alkaline medium,
which leads to the production of a considerable amount of mannitol due to alkalicatalyzed
epimerization of dextrose to fructose, which is reduced more readily than
dextrose. Sorbitol is industrially produced either by catalytic hydrogenation of dextrose,
which produces less than 2% mannitol, or by catalytic hydrogenation of
sucrose as a mixture with mannitol.
3.7