Fermentation Production Process, Extraction and Purification Technology of Citric Acid, and Its Fundamental Role in Food Flavoring

Citric acid can also be used in combination with sodium bicarbonate in effervescent tablets and granules to generate carbon dioxide bubbles, improving taste and solubility. By precisely controlling the amount of citric acid added, food manufacturers can stabilize product quality and meet consumer taste demands.

Citric acid, as an important organic acid, is mainly produced industrially through biological fermentation, a mature process with large yields. Citric acid production uses starchy raw materials such as corn, cassava, or molasses as carbon sources, and *Aspergillus niger* as the fermentation strain. After liquefaction and saccharification, the raw materials are made into a saccharified broth. This broth is adjusted to a suitable concentration and pH value before inoculating with a *Aspergillus niger* spore suspension. Sterile air is introduced into the fermenter, and the temperature and stirring speed are controlled for deep fermentation. During fermentation, *Aspergillus niger* metabolizes sugars to produce citric acid, while small amounts of isocitric acid and oxalic acid are produced as byproducts. The fermentation cycle is typically five to seven days, with an acid production rate exceeding 100 grams per liter. After fermentation, the bacterial cells are inactivated by heating, and the mycelium is removed by filtration, yielding the citric acid fermentation broth.

Extraction and purification of citric acid are crucial steps in obtaining high-quality products. Traditional processes use the calcium salt method, adding calcium carbonate or calcium hydroxide to the fermentation broth to form calcium citrate precipitate. After washing and desaccharification, acid hydrolysis is performed, replacing citric acid with sulfuric acid. Anhydrous citric acid or citric acid monohydrate is then obtained through decolorization, ion exchange, concentration, crystallization, centrifugation, and drying. Modern processes employ chromatographic or membrane separation technologies to improve yield and product purity while reducing wastewater discharge. Citric acid is a white crystalline powder, odorless, with an extremely sour taste, readily soluble in water, and its aqueous solution is strongly acidic. Its sour taste is pure and refreshing, disappearing quickly after consumption, and unlike other acidulants, it has no aftertaste of bitterness, making it an excellent food acidulant.

The fundamental role of citric acid in food flavoring lies in its wide application as an acidity regulator and flavor enhancer. In the beverage industry, citric acid is used to adjust the sweet-sour ratio of carbonated beverages, fruit juice beverages, and functional beverages, enhance fruit flavor, and inhibit microbial growth. In confectionery and jam production, citric acid can regulate gelation conditions, control the sugar-acid ratio, and improve product taste and shelf life. In frozen drinks, citric acid neutralizes the greasiness of milk fat, enhancing the refreshing taste. In condiments, citric acid is used to adjust the acidity and preserve freshness in soy sauce, vinegar, and salad dressings. Citric acid can also be used in combination with sodium bicarbonate in effervescent tablets and granules to generate carbon dioxide bubbles, improving taste and solubility. By precisely controlling the amount of citric acid added, food manufacturers can stabilize product quality and meet consumer taste demands.