Fructose, mannitol produced from

Sorbitol can be made by the reduction of three naturally occurring hexoses, D-glucose, D-fructose and L-sorbose. D-Mannitol and L-iditol, respectively, are concurrently produced from the ketoses. However, D-glucose, because of its greater availability, is the only practical source. 

Several heterofermentative LAB produce mannitol in large amounts, using fructose as an electron acceptor. Mannitol produced by heterofermentative bacteria is derived from the hexose phosphate pathway (Soetaert et al., 1999 Wisselink et al., 2002). The process makes use of the capability of the bacterium to utilize fructose as an alternative electron acceptor, thereby reducing it to mannitol with the enzyme mannitol dehydrogenase. In this process, the reducing equivalents are generated by conversion of one-third fructose to lactic acid and acetic acid. The enzyme reaction proceeds according to (theoretical) Equation 21.1 ... 

Alditols are mainly produced from aldoses or ketoses by hydrogenation or reduction with amalgams, complex hydrides or by electrolytic reduction. Xyhtol is prepared by reduction of D-xylose obtained by hydrolysis of natural xylems (hemicelluloses), D-glucitol is prepared from D-glucose and D-mannitol via hydrogenation of D-fructose obtained from either starch or invert sugar. 

Sorbitol is produced by high-pressure catalytic hydrogenation of glucose derived from cornstarch. It can also be produced as a co-product with mannitol if invert sugar (50% glucose, 50% fructose) is used as raw material. 

Reduction. Mono- and oligosaccharides can be reduced to polyols (polyhydroxy alcohols) termed alditols (glycitols) (1) (see Sugaralcohols). Common examples of compounds in this class are D-glucitol (sorbitol) [50-70-4] made by reduction of D-glucose and xyhtol [87-99-0] made from D-xylose. Glycerol [56-87-5] is also an alditol. Reduction of D-fructose produces a mixture of D-glucitol and D-mannitol [69-65-8]. 

Formerly the raw material for the production of nitromannitol, i.e. mannitol, was prepared from the juice of berries, in particular from Traxinus ornus (manna). At present it is produced by reducing D-mannose or D-fructose in the latter case D-sorbitol is also formed. 

Some microorganisms can specifically produce mannitol from glucose or fructose without making a sorbitol byproduct (Smiley et al., 1967 Song et al., 2002 Wisselink et al, 2002 Saha, 2003). Mannitol, at 180g/L, can be easily recovered from the fermentation broth by cooling crystallization. Thus, research efforts have been directed toward production of mannitol by fermentation and enzymatic means (Vandamme and Soetaert, 1995). In this paper, the authors review the production of mannitol by lactic acid bacteria. 

Several heterofermentative LAB belonging to the genera Lactobacillus, Leu-conostoc, and Oenococcus can produce mannitol from fructose effectively (Saha, 2003). In addition to mannitol, these bacteria may produce lactic acid, acetic acid, carbon dioxide, and ethanol. The process is based on the ability of the LAB to use fructose as an electron acceptor and reduce it to mannitol with the participation of the enzyme mannitol 2-dehydrogenase (EC 1.1.1.38). 

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