Citric acid is a weak organic acid with formula C6H8O7 which occurs naturally in citrus fruits. It is part of the citric acid cycle which occurs in the metabolism of all aerobic organism. Globally, more than a million tons of citric acid are produced annually and more than 70% of the total production are used in food and beverage industry as an acidifier or antioxidant to preserve or enhance the flavors and aromas of fruit juice, ice cream and marmalades. Citric acid exists in the form of anhydrous, which is crystallized from hot water, or monohydrate that crystallized from cold water. The anhydrous form of citric acid can be produced by heating citric acid monohydrate.
Citric acid is produced by submerged fermentation using fungus from different sources of carbohydrates such as molasses and starch based media. Calcium oxide is then added to form the slightly soluble tri-calcium citrate tetrahydrate as a precipitation. The precipitation is then removed by filtration and washed to remove impurities. It is then treated with sulfuric acid to form calcium sulphate, which is then filtered off. The liquid of citric acid is then treated with active carbon and passed through cation and anion exchanger. Finally, the liquid is concentrated in vacuum crystallizers at 20-25℃, forming citric acid monohydrate. A higher temperature in this step will result in citric acid anhydrous.
Citric acid is used as an agricultural repellent against frogs, especially in Hawaiian plants. As a corrosive and acidic compound, the amount of citric acid for plants must be specified. Adding too much citric acid can cause acidic soil, which can burn the plant root and cause the plant’s death.
Citric acid is widely used in food and beverage industry for different purposes. Some food that contains citric acid includes jellies, jams, candies, dairy product, frozen fruit, oils and animal feed. In beverages such as wine, ciders, soft drinks, and syrups also contain citric acid. Citric acid can be used for pH adjustment, preservation, as an antioxidant agent, sequestering agent, acidulate and flavour enhancer.
Citric acid is also used in pharmaceuticals. It is combined with bicarbonates to use as an effervescent and an anticoagulant. It is also used to adjust pH and as an antioxidant agent. Citric acid is used to increase the solubility of brown heroin. It is also used as feed in the production of antiviral tissues.
Citric acid is used to remove metal oxides for operational cleaning iron and copper oxides. In industrial application, citric acid is used for buffer agent and neutralize agent. It is also used in non-corrosive, non-toxic and biodegradable process and safety standards. Other uses includes ceramic manufacture, ion complexion, leather tanning, copper plating, floor cement, adhesive, waste treatment, electroplating, textile, bottle washing compound, etc.