Citric acid, in lemon juice

Acids and bases are common chemicals used every day. Some acids and bases are harmful if touched or swallowed. Some acids and bases are found in foods and are not harmful. Many acids and bases can be found around the home. Common household acids include acetic acid in vinegar, citric acid in lemon juice, and lactic acid in sour milk. It is the acids in these foods which give them their sour taste. Bases are the chemicaJ opposites of adds. Baking soda is a base. 

As is described in Section 25.3 of the text, acids denature enzymes. The citric acid in lemon juice denatures the enzyme that catalyzes the oxidation so as to inhibit the oxidation (browning). 

The citric acid in lemon juice decreases the fishy taste. 

Alkaloids vary widely in structure, from the simple to the enormously complex. The odor of rotting fish, for example, is caused largely by methylamine, CH3NH2, a simple relative of ammonia in which one of the NH3 hydrogens has been replaced by an organic CH3 group. In fact, the use of lemon juice to mask fish odors is simply an acid-base reaction of the citric acid in lemons with methylamine base in the fish. 

Introduction. Citric acid in citrus juices may be determined according to the Methods of Analysis as given in the AOAC (7). However, analysts who run a large number of tests daily have altered the method to speed up the titration and make calculations easier. One of these alterations is to use 0.3125 N sodium hydroxide rather than 0.1 N alkali. The use of the higher normality alkali is desirable especially when titrating samples of high density concentrates. It is almost imperative when titrating lemon concentrates. 

Pectin can also be added in the form of a solution. The required amount of pectin is dissolved in a small amount of hot water (about 80°C) and added to the fruit mixture. In this case the pectin is not added until after the sugar. Citric acid or lemon juice is also added in order to speed up the gelling process and improve the taste. The amount of pectin to be added depends on the original pectin content of the fruit and on the size of the container. Less pectin is needed for small containers than for bigger containers. 

The ionized polyphenols have a dark color. In the presence of citric acid from lemon juice, the anions are converted to the lighter-colored acids. 

With this huge amount of concentrations it is possible to detect frauds like the addition of sugar, exhaustive enzymatic treatment (galacturonic acid), addition of citric acid or lemon juice (e.g. in apple juice), extraction of orange peel (phlorin) or the usage unripe Suits (quinic acid in apple juice). 

Very early in the history of chemistry many substances were designated as acids, bases, and salts. Acids have a sour taste (e.g., citric acid gives lemon juice its sour taste) they dissolve certain metals and they also dissolve carbonate minerals to produce carbon dioxide. Bases have a bitter taste (e.g., sodium carbonate) they feel slippery when touched and they react with many dissolved metal salts to form precipitates. However, the most striking characteristic of bases is their ability to neutralize the properties of acids when a base reacts with an acid a salt is produced. 

CITRIC ACID. [CAS 77-92-9J. C.tH.,(OH)(COOH),. formula weight 192.12. white crystalline solid, mp 153. decomposes at higher temperatures, sp gr 1.542. Citric acid is soluble In H.O or alcohol and slightly soluble in ether. The compound is a trihasic acid, forming mono-, di-, and Iri- scries of salts and esters. Citric acid may be obtained (I) from some natural products, e.g., the free acid in the juice of citrus and acidic fruits, often in conjunction with malic or tartaric acid the juice of unripe lemons... 

The acidity of lemon juice is derived primarily from citric acid (H3Cit), a triprotic acid. What are the concentrations of H3Cit, H2Cit-, HCit2-, and Cit3- in a sample of lemon juice that has a pH of 2.37 and a total concentration of the four citrate-containing species of 0.350 M ... 

The organic acids of citrus fruit include a group of carboxylic acids (23) with different acids predominant in various component parts of the fruit. Citric acid is the main acid in the juice, representing from 80 percent of the total acidity in juice from ripened oranges, about 90 percent of that of grapefruit and nearly all of that of lemon. The pH of the juice greatly affects the sourness of the product (24) and is, in turn, affected by the cations, especially potassium. The major acids in citrus peel are malic, oxalic (25), malonic (26), and quinic (27). 

Citric acid makes up almost 85% of the total volume of the organic acid market, ft was first described in 1784 when isolated from lemon juice. In 1917, it was discovered that certain fungi accumulate citric acid. In 1923, the first US commercial plant was built to produce citric acid by fermentation citric acid is now used mainly in soft drinks, desserts, jams, jellies, candies, wines and frozen fruits. 

To prevent non-enzymatic browning, the fruit can be dipped in a 5% solution of citric acid (or in lemon juice). This is especially advisable in the case of sliced and diced apples where the acid content is low. The acid allows the light colour to be retained, while at the same time improving the taste of the pieces of apple. The colour of the fruit can be made even lighter by adding ascorbic acid to the dip. 

Substances which produce the hydrated hydrogen ion in aqueous solu tions are called acids Vinegar contains acetic acid, HC2H3O0 lemon juice contains citric acid, and sour milk and sauerkraut... 

When lemon juice is squirted into tea, the color becomes lighter. In part, the color change is due to dilution, but the main reason for the change is an acid-base reaction. What is the reaction Hint Tea contains polyphenols which are weak acids and lemon juice contains citric acid.)... 

Citric Acid. Thunberg (T21) has summarized the steps which led to the identification of citric acid in urine. Found in lemon juice by Scheele in 1784, citric acid was considered a typical plant acid until its presence was shown in milk in 1888. Classified among the normal metabolites by Thunberg since 1910, this acid was found first in animal urine after administration of citrate, then in normal human urine by Amberg and McClure (A6). Later on, it was found also in normal human plasma by Benni et al. (B9). 

Latin name of Geber. Geber described a substance with all the properties that we equate with citric acid today, but he knew nothing about its chemical structure. The first person to isolate the compound as a pure substance was the Swedish chemist Karl Wilhelm Scheele (1742-1786), who obtained citric acid from the juice of lemons. By the mid-nineteenth century, citric acid was being produced commercially in Italy from lemons and other citrus fruits. 

Besides other factors such as color and firmness, soluble solids to acids ratio is a good index to determine harvest time. For prunes, this value has to be 12-15 [13]. A maximum limit was set for citric acid to isocitric acid ratio to reveal the dilution factor of juices 130 for apricot puree and orange juice, 80 for grapefruit juice, and 185 for raspberry juice [14]. The total add content varies widely from <0.2% in papaya and avocado [3] to 8.3% in lemon juice [15]. 

Citric acid HsCgHsOv Found in lemon juice... 

Originally, the word acid described something that had a sour, biting taste. The tastes of vinegar (acetic acid) and lemon juice (citric acid) are typical examples. Substances with such tastes have other common properties, too. They impart certain colors to some organic substances, such as litmus, which is red in acid solutions they react with carbonate ions and release carbon dioxide they react with and neutralize a base and they release hydrogen when they react with particular metals. 

Many of the substances we encounter in our daily lives are acids, bases, or salts. Many fruits and vegetables are acidic because of the citric acid in them. Vinegar and lemon juice are acidic. Many household substances, including baking soda and window cleaners, are bases. Ionic compounds that are not acids or bases are classified as salts, of which table salt (NaCl) is certainly the most familiar. 

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