Aldehydes and related compounds

Although acetaldehyde is the primary aldehyde present in wines, there are reports of hydroxymethylfurfural, furfural, and higher aldehydes. Acetal and acetone are also found in some wines. 

Acetaldehyde is a normal by-product of alcoholic fermentation, but it may increase during aging owing to oxidation of ethyl alcohol or to the activity of film yeasts. It is easily fixed by sulfur dioxide, so that much of that present is bound.  

Methods. The total absence of aldehyde from some wines reported by Nelson and Wheeler (1939) was probably due to analytical errors. The primary methods employed 

The procedure of Jaulmes and Espezel (1935) is now widely used. It depends on fixing the aldehyde in a buffered sulfite solution, titrating the excess sulfite in acid solution, hydrolyzing the aldehyde-bisulfite complex under alkaline conditions, and then titrating the bisulfite released—which is equivalent to the aldehyde present. Joslyn and Comar (1938) studied this and other procedures. They noted that less than 100% of the aldehyde present is recovered. This procedure can be improved by controlling the pH when hydrolyzing the aldehyde-bisulfite complex, e.g., with a less alkaline solution such as bicarbonate. To improve the sensitivity of Jaulmes s procedure Roche (1948) recommended a more dilute iodine solution and a standard color to determine the end point. He proposed a dilute mixture of basic fuchsin and indigo carmine for this. 

A comparison of procedures for the determination of acetaldehyde was made by Iribarne, (1941). The colorimetric Schiff, the bisulfite procedure, and the hydroxylamine method were compared. In general, the bisulfite procedure gave a better and more regular recovery, but on 49 wines it showed only 101 mg. per liter of aldehyde, and the hydroxylamine, 104. 

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Weaver, J.W., Nielson, J.F. and Goldstein, I.S. (1960). Dimensional stabilization of wood with aldehydes and related compounds. Forest Products Journal, 10(6), 306-310. 

Interest in linkers for carbonyl compounds has only slowly emerged in recent years. The main driving force for the development of such linkers was the need for methods to prepare peptide aldehydes and related compounds (e.g. peptide trifluoromethyl ketones), which can be highly specific and valuable enzyme inhibitors [700,701], and are potentially useful for the treatment of various diseases. 

M. T. Reetz, Synthesis and Diastereoselective Reactions of N,N-Dibenzylamino Aldehydes and Related Compounds, Chem. Rev. 1999, 99, 1121—1162. 

Other aldehydes and related compounds have been reacted either alone or catalyzed with sulfuric acid, zinc chloride, magnesium chloride, ammonium chloride, or diammonium phosphate (94). Compounds such as l,3-bis(hydroxymethyl)-2-imidazolidone, glycol acetate, acrolein, chloroacetaldehyde, heptaldehyde, o- and p-chloro-benzaldehydes, furfural, p-hydroxybenzaldehyde, and m-nitrobenz-aldehyde all achieve the ASE by a bulking mechanism and not by low-level cross-linking. At weight gains of 15-25%, the highest ASE reported is 40%. 

The formation of off-flavours in beer has been reviewed [40], Autoxidation of the lipids present in beer produces carbonyl compounds with very low taste thresholds. In particular, linoleic acid is oxidized to trihydroxyoctadecenoic acids (Table 22.7) which break down into 2-/mAz.y-nonenal. This aldehyde and related compounds impart a cardboard flavour to beer at very low concentrations. Other carbonyl are formed from the lipids in beer by irradiation with light including the C9, Cjo, and Cu-alka-2,4-dienals (thresholds 0 5, 0 3 and 0 01 ppb respectively) [40]. The level of diacetyl and pentane-2,3-dione in a range of commercial beers is given in Table 22.11. Quantities in excess of 0 15 ppm impart a buttery flavour more noticeable in lagers than in ales. Bacterial contamination and petite mutants of yeast result in high levels of diacetyl. The sulphur compounds characterized in beer are listed in Table 22.19 with some threshold data. Dimethyl sulphide is the major volatile... 

Noma, Y., E. Akehi, N. Miki, and Y. Asakawa, 1992a. Biotransformation of terpene aldehyde, aromatic aldehydes and related compounds by Dunaliella tertiolecta, 31 515 517. 

Noma Y, Okajima Y, Takahashi H, Asakawa Y. Biotransformation of aromatic aldehydes and related compounds by Euglena gracilis Z. Phytochemistry 1991 30 2969-2972. 

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