Organic acids in grapes

The principal organic acids in grape are L(+)-tartaric, L(—)-malic, shikimic and citric acid. Gluconic, 2-keto-D-gluconic and mucic acids are present in rot grapes as metabolites of Botrytis Cinerea. The structures of these compounds are reported in Figure 1.2. 

Mato, I., Suarez-Luque, S., and Huidobro, J.F. 2005. A review of the analytical methods to determine organic acids in grape juices and wines. Food Research International 38 1175-1188. 

The products of yeast autolysis, such as amino acids may also play a role in wine flavor. The autolysate by-products may also serve as substrates for secondary fermentations. Malic and tartaric acids, the principle organic acids in grape must and wine, can also serve as substrates for secondary fermentation. 

Ascorbic acid (vitamin C) is utilized as a cofactor to stabilize the chloroplast stroma, in quenching free radicals and reacting with hydroxy radicals and in the biosynthesis of tartaric acid and oxalic acid (6), important organic acids in grapes, and many vegetables. The effect of CA on ascorbic acid content differs with commodity,... 

The main organic acids in grapes are described (Table 1.1) according to the conventional Fischer system. Besides tartaric acid, grapes also have a stereoisomer in which the absolute configuration of the two asymmetrical carbons is L, but whose optical activity in water, measured on a polarimeter, is d (or +). There is often confusion between these... 

Organic acids in grapes are partly neutralized by potassium and calcium ions, forming salts. This... 

Tartaric acid is the main organic acid in grapes at the levels of 5-10 g/L, followed by malic acid (2-4 g/L) and a small amount of citric acid. Other acids such as succinic, acetic, lactic, and propionic acids are formed in limited content in wines during fermentation. An increased content of these acids indicates improper fermentation. The content of organic acids in commercial Austrian and Spanish red and white wines is shown in Table 10.6 [16,17]. 

Delmas J, Poitou N, Levadou B 1963 Chromatographic separation of the principal organic acids in grape leaves. Chim Anal (Paris) 45 63-65... 

Mato, I., S. Suarez-Luque, and J. F. Huidobro. 2007. Simple determination of main organic acids in grape juice and wine by using capillary zone electrophoresis with direct UV detection. Food Chem. 102 104-112. 

Furfural and 5-HMF were measured and considered as quality indicators. In particular, fructose and glucose undergo degradatirMi phenomena involving furfurals formation, tartaric, and malic acids are the main organic acids in grape finally, the loss of water has to be monitored since it represents a... 

The major organic acids in fruits other than grape are usually citric and malic acids (Table III). However, quinic acid, in addition to citric and malic acids, was a principal acid in peaches (71, 72). The main acid... 

The term wine refers to the natural beverage produced from the juice of sound and ripe grapes, in strict accordance with federal and state regulations. The stabilization principles discussed will have equal application to fruit wines in general except for tartrate stabilization since tartaric acid, the primary organic acid of grapes, is not found in any other fruits commonly used in winemaking. 

Figure 7.4. HPLC analysis of organic acids in white wine and grape must using a resin column with refractive index and UV detection at 210nm. HPLC conditions two Polypore H (10 pm, 220 x 4.6mm) mobile phase 0.01 N H2S04 flow rate 0.2mL/min at 60°C. Reprinted with permission from reference 13.

Figure 10.208 Ion-exclusion chromatography eluent 5mmol/L H2SO4 detection UV of organic acids in a freshly squeezed grape (210nm) sample freshly squeezed Italian juice utilizing UV detection. Separator column grape juice peaks (1) tartrate, (2) malate, and Shim-pack IE column temperature 60°C (3) fumarate (see [311]).

The complexity of wine composition is a central reason for the vast variety of wines in the marketplace. In addition to water and ethanol, the major components, a variety of organic acids as well as metal ions from minerals in the skin of the grape are present. Initially, all of these substances remain dissolved in the bottled grape juice. As the fermentation process occurs, the increasing alcohol concentration in the wine alters the solubility of particular combinations of acid and metal ions. Unable to remain in solution, the insoluble substances settle as crystals. Since the process of red-wine making involves extended contact of the grape juice with the skins of the grapes (where the minerals are concentrated), wine crystals are more common in red wines than in white wines. 

Grapes are one of the few fruit crops that contain a significant amount of the weak organic acid known as tartaric acid, HOOC-(CHOH)2-COOH. More than half of the acid content of wine is ascribed to tartaric acid. As a weak acid, tartaric acid partially ionizes in water to yield the bitartrate or hydrogen tartrate ion ... 

Although their amounts are low in wines, organic acids are important constituents which affect the sensory properties of wines, particularly tartness (10). Berg et al. (17) reported both the threshold and minimum concentration differences for a number of acids found in grape wines. In a comprehensive study and review of acids, Amerine et al. (42)... 

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