The sum formula of citric acid is C₆H₈O₇, an important organic acid. It is a colorless crystal, odorless, has a strong acidic taste and is easily soluble in water. It is a natural preservative and food additive.
What properties does citric acid have?
How is citric acid produced in nature?
How is citric acid produced artificially?
What properties does citric acid have?
citric acid is a white crystalline powder at room temperature, odourless and extremely acidic in taste, with a density of 1,542 g/cm3, a melting point of 153-159 °C and decomposes above 175 °C, releasing water and carbon dioxide. citric acid is easily soluble in water with a solubility of 59% at 20 °C, and the pH of its 2%of aqueous solution is 2.1. The crystalline form of citric acid varies due to different crystallization conditions. In dry air it is slightly weathered and hygroscopic in humid air. It can be decomposed into various products during heating and with acids, alkalis, glycerin, etc. react. When citric acid is dissolved in ethanol, it reacts with ethanol to produce ethyl citrate.
How is citric acid produced in nature?
Natural citric acid is widely used in nature. Natural citric acid is found in bones, muscles and blood of plants such as lemons, citrus fruits, pineapples and other fruits and animals. Synthetic citric acid is obtained by fermentation of sugary substances such as sugar, molasses, starch and grapes.
Many fruits and vegetables, especially citrus fruits, contain a lot of citric acid, especially lemons and limes – they contain a lot of citric acid, up to 8% after drying (the amount in the juice). about 47 g/l). Citrus fruits contain between 0.005 mol/L orange and grape and 0.30 mol/L lemon and lime. This content varies with the growth of different varieties and plants.
How is citric acid produced artificially?
The microbial fermentation method is used in the industrial production of citric acid, and only some types of aspergillus and yeast are valuable. Among them, Aspergillus niger is the most competitive strain in the industry, and the most competitive yeasts are lipolytic pseudosaccharides. Silk yeast and Saccharomyces cerevisiae, etc.
Aspergillus niger is cultivated on agar and forms limited colonies on agar. After 10–14 days of cultivation at room temperature, it becomes a rich and dense sporophore. The colonies are black and sometimes dark brown. Considering that the citric acid producing bacteria should have the characteristics of strong acid production ability and high citric acid concentration, acid filter paper process, discoloration circuit process and single spore transplantation process can be used, to isolate Aspergillus niger, to avoid this interference of other different bacteria. Become Aspergillus niger for the production of citric acid.
The yeasts that can be used for the production of citric acid are Candida lipolytica and Candida quaternaria. The former has a strong ability to break down fat, and the better carbon source is n-alkane. The latter can be fermented from alkanes to citric acid and can also be fermented from sugars to citric acid. The pH value of the yeast fermentation is 3.5 to 4.0.
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