Organic acids in wines

6 Tests for predicting wine stability in relation to crystal precipitation and 

Organic acids make major contributions to the composition, stability and organoleptic qualities of wines, especially white wines (Ribereau-Gayon etal., 1982) (Jackson, 1994). Their preservative properties also enhance wines microbiological and physicochemical stability. 

dry white wines not subjected to malo-lactic fermentation are more stable in terms of bitartrate (KTH) and tartrate (CaT) precipitation. Young white wines with high acidity generally also have greater aging potential. 

Red wines are stable at lower acidity, due to the presence of phenols which enhance acidity and help to maintain stability throughout aging. 

Most organic acids in must and wine have one or more chiral centers. The absolute configuration of the asymmetrical carbons is deduced from that of the sugars from which they are directly 

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Moreira, J.L. and Santos, L., Analysis of organic acids in wines by Fourier-transform infrared spectroscopy, Anal. Bioanal. Chem., 382, 421, 2005. 

Anon (n.d.d) Dionex application note number 21 The determination of organic acids in wines. Available as a downloadable file from the Dionex website (http //www.Dionex.com). 

Maujean, A. (2000). Organic acids in wine. In Handbook ofFnology vol. 2 The Chemistry of Wine, Stabilization and Treatments (pp. 3-39). New York John Wiley Sons, LTD. 

It means the sum of organic acids in wine determined by HPLC have to be lower than the sum total acidity and wine ashes alkalinity determined by titration. 

Preparation of the sample for analysis of organic acids in wine is analogous to the method reported for preparation of the must sample by using SPE C18 cartridge (paragraph 1.2.2) but, instead of collecting the eluate of a lmL diluted sample in a 20-mL volumetric flask, a 10-mL volumetric flask is used (the final sample is diluted 10-fold). To improve... 

The method proposed by Shneider et al. (1987) for analysis of organic acids in wine can be applied to perform the simultaneous determination of organic acids, glucose and fructose, glycerol and ethanol by using the... 

The most common analytical method for detection of benzoic acid or sorbic acid has been reversed-phase HPLC (Saad et al., 2005). Organic acids in wine vinegars have also been detected by reversed-phase HPLC (RP-HPLC) using two C18 columns, UV detection at 210 nm, and sample filtration through Sep-Pack C18. However, complete separation of organic acids has not been achieved with this procedure (Morales, Gonzalez, and Troncoso, 1998). 

Deng, C.R., 1997. Determination of total organic acids in wine by interfacial devia-tization gas chromatographic methods. Sepu 15 505-507. 

A final property of the majority of organic acids in wine is that they have one or more asymmetrical carbons. This is characteristic of biologically significant molecules. 

Ash includes all the cations, other than ammonium, that combine with organic acids in wine. Normally, ash is white or grayish. Green ash that turns red in an acid medium indicates a high manganese concentration. Yellow is a sign that there is a high iron content. 

Vonach, R., Lendl, B., and Kellner, R. High-performance liquid chromatography with real-time Fourier-transfonn infrared detection for the determination of carbohydrates, alcohols and organic acids in wines. J. Chwmatogr. A, 824, 159-167, 1998. 

Castineira, A., Pena, R. M., Herrero, C., and Garcii. ia-Martin, S., Analysis of organic acids in wine by capillary electrophoresis with direct UV detection, J. Food Comp. Anal, 15, 319, 2002. 

Applications Notwithstanding the limitations, there are a limited number of specific applications in which flow-cell LC-FTIR can be quite useful to obtain specific quantitative and structural information in a convenient manner. The application area of flow-cell FTIR is limited to samples with relatively high analyte concentrations, as is the case in, for instance, the analysis of carbohydrates, alcohols, and organic acids in wines and sugars in soft drinks. SEC, as used for the separation of synthetic polymers, is also well suited to be coupled with FTIR by flow cells. Polymer samples are often available in large quantities and low detection limits are usually not required. In addition, the separation process in SEC is essentially independent of the choice of eluent, provided the sample is fully soluble and no analytestationary phase interactions take place. Consequently, IR-favorable eluents can be selected. Therefore, SEC-flow-cell-FTTR is a valuable tool for the rapid, selective, and quantitative analysis of the chemical composition of polymers as a function of their hydrodynamic volume. 

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