Citric acid,

Citric acid is the most widely used acid in fruit-flavoured beverages. It has a light fruity character that blends well with most fruit flavours, which is to be expected as it occurs naturally in many fruit types. For example, unripe lemons contain 5-8% citric acid. It is also the principal acidic constituent of such fruits as blackcurrants 

Citric acid, 2-hydroxy-l,2,3-propane tricarboxylic acid, HOOCCH2C(OH)(COOH)CH2COOH 192.1 152-154 

Citric acid (pKi = 3.09 pK2 = 4.74 pKs = 5.41) is utilized in candy production, fruit juice, ice cream, marmalade and jelly manufacturing, in vegetable canning and in dairy products such as processed cheese and buttermilk (aroma improver). It is also used to suppress browning in fruits and vegetables and as a synergetic 

Despite the popularity of citric acid as a food additive and preservative, its sharp and overwhelming acidic taste is, however, inclined to overpower the flavor of sweeteners or other flavorants that may be present in a foodstuff. Citric acid also presents a short-lived tartness flavor. Other disadvantages have also been noted when using citric acid as a food additive. For example, due to its hygroscopic nature, it tends to cake when used in dry powders such as soft drink or beverage mixes. It also has an uneven particle size and is not always free-flowing. However, despite these few drawbacks, citric acid is by far the most commonly used food acidulant. The initial sharpness associated with citric acid is preferable in some end products such as citrus-flavored drinks (Fowlds, 2002). 

The inhibitory effect of citric acid on Listeria monocytogenes growth has been found to be much more evident than the inhibitory effect of ascorbic acid. The difference in inhibition between both acids is most obvious when the temperature is higher. Because of the pf( values of citric acid (pKj = 3.14, pK2 = 4.77, and p/ 3 = 6.39), it dissociates strongly inside microbial cells (Carrasco, Garcia-Gimeno, and Seselovsky, 2006). 

The major pathway for the formation of citric acid is through the condensation of oxaloacetate and acetyl-CoA catalyzed by citrate synthase, the first enzyme in 

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Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

The BZ reaction involves the oxidation of an organic molecule (citric acid, malonic acid (MA)) by an... 

Conversion of sodium citrate into citric acid. 

Take two test-tubes A and B in A place about 5 ml. of neutralised tartaric acid solution and in B place 5 ml. of distilled water. To each solution add 3-4 drops of ferric chloride solution. Place a piece of white paper under the tubes, look down their length and note that A is definitely yellow compared with the control tube B. This yellow colour is given by a-hydroxy-carboxylic-acids, lactic acid, tartaric acid, citric acid. 

Example. Heat together under reflux 0-5 g. of citric acid, 3 ml. of benzylamine and 015 g. of ammonium chloride for i hour. Cool, shake with about 10 ml. of water and filter off the solid. Recrystallise from ethanol small white crystals m.p. 170 . (M.ps., pp. 543-545 )... 

Sulphuric add test. Heat 0 5 g. of citric acid or a citrate with 1 ml. of H2SO4 CO and COg are evolved and the mixture turns yellow, but does not char. Acetone dicarboxylic acid, OC(CH2COOH)g, is also formed, and is tested for after heating the mixture for 1 minute cool, add a few ml. of water and make alkaline with NaOH solution. Add a few ml. of a freshly prepared solution of sodium nitroprusside and note the intense red coloration (see Test 4 a) for ketones, p. 346). 

A) AMMONIUM SALTS. R COONH4. Ammonium salts of formicy acetic oxalic, succinic, tartaric, citric acid benzoic, salicylic (and other substituted benzoic acids) phthalic and cinnamic acids. 

If a phenol is not indicated, the solution may contain an aliphatic acid. Transfer to a distilling-flask, make definitely acid with dih H2SO4, and distil the volatile formic and acetic acids if present will distil over. If the distillation gives negative reactions, test the residual solution in the flask for oxalic, succinic, lactic, tartaric and citric acids and glycine, remembering that the solution is strongly acid. 

Supplement (combined with Volume IV) III, 2nd 1929 195-449 Hydroxy-carboxylic acids Carbonic acid, 3. GlycoUic acid, 228. Lactic acid, 261. Tartaric acid, 481. Citric acid, 556. Urea, 42. Cyanamide, 74. Thiocyemic acid, 140. 

Caustic alkalis. Dilute by drinking much water, followed by vinegar, lemon or orange juice, or solutions of lactic acid or citric acid. Milk may then be given but no emetics. 

Citric acid has three CO2H groups Which if any of them are... 

The enzyme acomtase catalyzes the hydration of aconitic acid to two products citric acid and isocitnc acid Isocitnc acid is optically active citric acid is not What are the respective con stitutions of citric acid and isocitnc acid" ... 

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