Mannitol salt formation

Reduction of fructose to mannitol brings about reoxidation of reduced NADH formed during heterolactic fermentation of glucose  

Energetically, this permits acetyl phosphate to be hydrolyzed (by acetate kinase) to acetic acid (yielding one ATP) rather than being reduced to 

Fructose-Supplemented Apple Rogosa Broth Test tubes and closures 

Prepare fructose-supplemented Apple Rogosa Broth as described previously, to include an additional 2% (wt/vol) fructose. 

Transfer 5 mL aliquots to test tubes, stopper, and sterilize by autoclaving. 

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Mannitol salt formation is also used as a laboratory diagnostic test for the separation of homofermenters (which do not reduce fructose in formation of mannitol) from heterofermenters, which utilize the pathway described above. From the winemaker s perspective, the importance of mannitol formation, by itself, is uncertain except to increase the potential for acetic acid production. Sponholz (1993) reports that it is associated with bacterially mediated deterioration in high-pH sweet wines. He concludes that the best technique for the prevention is acidulation, whereby the pH is lowered to the point (<3.5) at which the likelihood of growth of most spoilage lactics is precluded. 

The formation of mannitol is detected by growing the bacterium in the fructose-enriched medium described by Pilone etal. (1991). Formation of mannitol salt crystals in the dried medium are detected visually as large rosettes without further magnification. It is essential to allow a few days for crystal formation at 25°C/77°F after evaporating the water at 37°C/99 F because crystals are often not seen prior to the final drying time. 

Complex-formation with a cation does not, in itself, affect the optical rotatory power of a carbohydrate. However, complex-formation is often accompanied by a change of conformation that causes a change in the optical rotation. For example, the rotation of D-glucitol and, to a lesser extent, of D-mannitol is affected by the presence of cations, in the order Na" " < Mg < Zn " " < Ba " < Sr " " < Ca (see Section III,1). The optical rotation of methyl jS-o-ribopyranoside and ) D-lyxopyranoside would, undoubtedly, be substantially changed by complex-formation, but this experiment has, apparently, not been reported. Therefore, a chmige of optic rotation on addition of a salt can be regarded as proof of complex-formation, but lack of such change does not necessarily indicate that no complex is formed. 

Chiral 18-crown-6-polyethers. British chemists have prepared optically pure chiral crown ethers, such as LL-(l) and DD-(2) from L-tartaric acid and D-mannitol, respectively, and have shown by NMR spectra that they exhibit differentiation in complex formation between R- and S-a-phenylethylam-monium hexafluorophosphate. Thus DD-(2) complexes preferentially with the cation of the R-salt. 

Thionyl chloride, as well as other inorganic acid chlorides, reacts with polyols to form mixed esters (see under Sulfate esters. Chapter III). In the presence of pyridine, partial chlorohydrin formation may occur (95), Selenium oxychloride forms a selenite ester upon reaction with mannitol (96), Phosphorus pentachloride yields unsaturated chlorohydrins of mannitol and galactitol which have the composition CeHeCU (97), Extremely interesting are the so-called complexes of alditols with various inorganic polybasic acids, their salts, or anhydrides in aqueous solutions. Complexes with boric, molybdic, tungstic, and other acids, as well as the oxides of antimony and arsenic, have been reported. It is believed that these complexes are true esters with one or more moles of alditol, a chelate type of structure being involved at some point. For the hexitols a compound with boric acid such as the following is postulated (98),... 

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