Acids in wines

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

I. J. Kosir, J. Kidric 2001, (Identification of amino acids in wines by one- and two-dimensional nuclear magnetic resonance spectroscopy), J. Agric. Food Chem. 49, 50—56. 

T. Erdoss, TLC identification of the Preservatives Salicylic Acid, Sorbic Acid, and Benzoic Acid in Wine , Proceedings of Wines, Mesogazdasagi Klado (Agricultural Publisher), Budapest, 1986, pp. 164-167. 

Hydrolyzable Tannins. The hydrolyzable tannins are composed of one glucosidic molecule to which are bonded different phenolic moieties the most important of these are gallic acid (15) and the lactone of its dimer, ellagic acid (16). These are not the natural tannins of grapes, but they are the principal commercial tannins (tannic acid) authorized by legislation to be added to wines. The oak tannins also belong to this family and may be added to wines stored in wooden casks. The presence of ellagic acid in wine, reported in the literature, needs to be confirmed. 

Total Acid. Simple titration procedures are used to determine total acidity. Problems arise because of the widely varying amounts of different acids in wines tartaric, malic, citric, lactic, succinic, acetic, etc. Different pKtt values for these acids make it impossible to predetermine easily the correct pH of the endpoint. Since a strong base is being used to titrate relatively weak acids, the endpoint will be greater than pH 7. In this country phenolphthalein (8.3) or cresol red (7.7) endpoints or a pH meter to 9.0 have been used (3, 6, 12, 76, 77) and the results are expressed as tartaric acid. The result at pH 7.7 X 1.05 approximately equals the result of titrating to pH 8.4. In Europe pH 7 is usually the endpoint, in France the results are expressed as sulfuric acid, and in Germany as tartaric or in milliequivalents (78). 

The possibility of determining the acids in wines from the titration curve using special equations has been extensively investigated in Portugal by Pato and coworkers (79). To keep the ionic force constant, appropriate dilution is needed. Tartaric, malic, lactic, and succinic acid were determined in musts and wines. 

Fumaric Aero Inhibition. Another means of preventing malo-lactic fermentation is to add fumaric acid after alcoholic fermentation is complete (45, 46, 47,48). The inhibition is relative and its extent is dependent on the amount added. The susceptibility to fumaric acid is also dependent on the strain of malo-lactic bacteria tested (49). However, we know of no case where fumaric acid addition at the levels suggested by Cofran and Meyer (45) (about 0.05%) did not delay malo-lactic fermentation under normal winemaking conditions. This includes several experiments from our pilot winery (50). Nevertheless, we have not been hasty to recommend the use of fumaric acid as an inhibitor because 1) of the difficulty in solubilizing the acid in wine 2) we do not know the mechanism of action of its inhibition [Pilone (47, 48) has shown that the bacteria metabolize low levels of fumaric acid to lactic acid but, at inhibitory levels at wine pH, the acid is bactericidal] and 3) of the desirability of minimizing the use of chemical additives. 

In discussing the studies of Brechot et al. (24) and Peynaud et al. (25), Kunkee (I) found it odd that bacteria which ordinarily produce d or DL-lactic acid from glucose produce L-lactic acid in wine as a result of malo-lactic fermentation. Peynaud et al. (26) reported that organisms which produced only D-lactic acid from glucose produced only L-lactic acid from L-malic acid. He postulated further that the malo-lactic fermentation pathway has no free pyruvic acid as an intermediate because the optical nature of L-malic acid would be lost when it was converted to pyruvic acid since pyruvic acid has no asymmetric carbon atom. Therefore, if pyruvic acid were the intermediate, one would expect d, l, or DL-lactic acid as the end product whereas L-lactic acid is always obtained. These results lend considerable support to the hypothesis that free pyruvic... 

Decarboxylation 21 Malic acid to lactic acid (in wines) amino acids to amines (histamine and tyramine accumulate in soft cheeses because of surface growth of lorulopsis Candida and Debaryomvces kloeckera). 

T Bauza, A Blaise, F Daumas, JC Cabanis. Determination of biogenic amines and their precursor amino acids in wines of the Vallee du Rhone by high-performance liquid chromatography with precolumn derivatization and fluorimetric detection. J Chromatogr A 707 373-379, 1995. 

An example of separation obtained with this method is reported in Fig. 2. Falque and Fernandez (23) study the influence of time of contact with the skins on the composition of the volatile fraction and of the carboxylic acids in wine produced from Treixadura grapes. Also, these authors quantify glycerol and ethanol, besides carboxylic acids and sugars, through the use of an Aminex HPX-87H (300 X 7.8 mm) column, but with the mobile phase of H2S04 0.65 mM at 75°C and a flow of 0.7 ml/min. They use a UV detector at 214 nm and an RI in series. The sample requires only a filtration at 0.45 /im, as described in their survey (24). 

R Farre, G Font, A Fuster. Determination of 5-nitrofurylacrylic acid in wines by high-performance liquid chromatography. J Chromatogr 445 264 -267, 1988. 

A Amati, M Castellari, I Ensini, U Spinabelli, G Arfelli. Determination of sorbic acid in wines with a hydrogen sulfonated divinyl benzene-styrene copolymer HPLC column. Chromatogr 44 645-648, 1997. 

Most HPLC applications used for phenolic analysis simply allow the room temperature to determine the operating temperature of the column, but elevated temperatures of between 30°C and 40°C are often applied for phenolics and derivatives in apples (14), carrots (15), apple juice (6,13), bilberry juice (16), and for cis-trans isomers of caffeic and p-coumaric acids in wines (17). Generally, a change in temperature has only a minor effect on band spacing in reversed-phase HPLC and has essentially no effect in normal-phase separations. Thermostatic control of the column temperature is generally recommended to provide reproducible retention. 

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). 

Quantitative (total tartaric acid). 100 c.c. of the vinegar are treated in a beaker with 1 c.c. of 20% potassium acetate solution and 15 grams of powdered potassium chloride. When the latter has dissolved, 20 c.c. of 95% alcohol are added, the subsequent procedure being as indicated for the determination of the total tartaric acid in wine q.v., p. 193). 

M. Albareda-Sirvent and A.L. Hart, Prebminary estimates of lactic and malic acid in wine using electrodes printed from inks containing sol-gel precursors, Sens. Actuators B Chem., 87(1) (2002) 73-81. 

Valero, E., Millasn, C., Ortega, J. M., and Mauricio, J. C. (2003). Concentration of amino acids in wine after the end of fermentation by Saccharomyces cerevisiae strains. ]. Sci. Food Agric. 83, 830-835. 

Herraiz, T., Huang, Z., and Ough, C. S. (1993). l,2,3,4-Tetrahydro-P-carboline-3-carboxylic acid and 1-Methyl-1,2,3,4-tetrahydro-P-carboline-3-carboxylic acid in wines. ]. Agric. Food Chem. 41, 455—459. 

Bioletti, F.T. Sulfurous Acid in Wine Making, Eighth Intern. Cong. Appl. 

This is the main reaction of MLR Chemically it consists of a simple decarboxylation of the L-malic acid in wine into L-lactic acid. Biochemically, it is the result of activity of the malolactic enzyme, characteristic of lactic acid bacteria. This transformation has a dual effect. On the one hand, it deacidifies the wine, in other words, it raises the pH, an effect that is greater at higher initial quantities of malic acid. It also gives the wine a smoother taste, replacing the acidic and astringent flavour of the malic acid, by the smoother flavour of the lactic acid. 

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. 

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