Wines mannitol

Sorbitol and Mannitol. Sorbitol is present in fruits but not in grapes. A method for its determination is required to detect illegal blending of fruit wines with grape wines. Mannitol is produced by bacterial spoilage. Sorbitol dehydrogenase and thin-layer chromatography have been used for their simultaneous determination (5). 

Quality standards for some flavor constituents will eventually be developed—linalool for muscats, for example, and perhaps phenethanol for certain types of wine. Kahn and Conner (124) have published a rapid GLC method for phenethanol. It has been suggested (60) that detection of bacterial activity from the presence and amount of minor bacterial byproducts (arabitol, erythritol, and mannitol) may be useful. Based on GLC determination of carbonyls, esters, and higher alcohols, beers were accurately classified into three categories (125). Anthocyanin content has been determined quantitatively by using molar absorbance values for five anthocyanin pigments (126). 

Some strains of L. brevis cause mannitol taint by enzymatic reduction of fructose to mannitol. Mannitol is a polyol produced in heterofermentative metabolism. Its perception is often complicated as it generally exists in wine alongside other defects, but it is usually described as viscous and ester-like, combined with a sweet and irritating finish (Du Toit and Pretorius 2000). Mannitol is usually produced in wines that undergo MLF with a high level of residual sugars still present. 

Mannitol is derived from reduction of the Ci on mannose. In wine, it is produced by the reduction of the C2 on fructose by lactic bacteria. Mannitol is usually present in very small quantities. Higher concentrations are due to lactic bacteria or possibly Botrytis cinerea. Abnormally high concentrations indicate severe lactic spoilage. 

Sorbitol results from the reduction of the Ci on glucose. This diastereoisomer of mannitol is totally absent from healthy grapes. Varying quantities are formed when Botrytis cinerea develops. Alcoholic fermentation produces approximately 30 mg/1. Lactic bacteria do not form this compound. Large quantities of sorbitol indicate that wine has been mixed with wines made from other fruits. Besides rowan berries Sorbus aucuparia), from which it takes its name, apples, pears and cherries also have a high sorbitol content. 

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. 

PiLONE, G.J., M.G. Clayton, and RJ. van Duivenboden. 1991. Characterization of wine lactic acid bacteria Single broth culture for tests of heterofermentation. Mannitol from fructose and ammonia from arginine. Am. J. Enol Vitic. 42(2) 153-157. 

Mannitol. Whereas mannitic fermentations are seldom a problem where sulfur dioxide, pure yeasts, and temperature control are employed, Martucci (1941) has reported them in Argentina. He recommended control of the must acidity, since a high pH also favored such spoilage. A complicated polaiimetric procedure for mannitol (a sugar alcohol) in wines was presented by Salani (1937). Formation of mannite during dialysis of musts at low temperatures (8° to 10° C. (46.4° to 50° F.)) in the presence of chloroform was reported by Barbera (1933b) (possibly owing to enzyme action). 

Adulteration of grape wine by the addition of fruit wines may be detected because of the presence of sorbitol in the latter. Litterscheid s o-chlorobenz-aldehyde method appears to be the best of the various tests proposed. However, mannitol may interfere if present in excessive amounts (120 120a). 

The natural variation range of GF in wines, as long as they have not been produced from noble rot material, lies between 8 and 10. Values above 12 indicate an additive. Low amounts of additive cannot be safely detected using the GF. More suitable is then the use of GC-MS to test the wine for the by-products of the technical synthesis of glycerol, e. g. 3-methoxypropanediol or cyclic diglycerols. Sorbitol is found in very low amounts. D-Mannitol is not present in healthy wines, but is present in spoiled, bacteria-infected wines at levels up to 35 g/1. 

Additional yeast spoilage is induced by species of the genera Candida Mycoderma), Pischia and Hansenula (Willia). Other microorganisms are involved in the formation of viscous, moldy and ropy wine flavor defects. Bacterial spoilage may involve acetic acid and lactic acid bacteria. In this case vinegar or lactic acid souring is detectable. It has usually been associated with mannitol fermentation which may result in considerable amounts of mannitol. 

During a botrytis attack, other polyols (mannitol, erythritol and meso-inositol) are formed and their concentrations increase in the grape (Bertrand et ah, 1976). B. cinerea also produces a glucose polymer, which accumulates in contaminated grapes. Its concentration can attain 200 mg/1 in must. This glucan is often at the root of subsequent wine clarification difficulties (Dubourdieu, 1978). 

---