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The production of citric acid (CA) is achieved by growing strains of A. niger in a nutrient rich medium that includes high concentrations of sugar and mineral salts and an acidic pH of 2.5-3.5. [27] Many microorganisms produce CA, but Aspergillus niger produces more than 1 million metric tons of CA annually via a fungal fermentation process. [28]
Overview of the citric acid cycle. The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle) [1] [2] —is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, proteins, and alcohol.
Citric acid sold in a dry powdered form is commonly sold in markets and groceries as "sour salt", due to its physical resemblance to table salt. It has use in culinary applications, as an alternative to vinegar or lemon juice, where a pure acid is needed. Citric acid can be used in food coloring to balance the pH level of a normally basic dye.
Humans have used fermentation in production of food for 13,000 years. [5] Humans and their livestock have microbes in the gut that carry out fermentation, releasing products used by the host for energy. [6] Fermentation is used at an industrial level to produce commodity chemicals, such as ethanol and lactate.
Despite the bactericidal effects of ethanol, acidifying effects of fermentation, and low oxygen conditions of industrial alcohol production, bacteria that undergo lactic acid fermentation can contaminate such facilities because lactic acid has a low pKa of 3.86 to avoid decoupling the pH membrane gradient that supports regulated transport.
It functions as a pace-making enzyme in the first step of the citric acid cycle (or Krebs cycle). [5] Citrate synthase is located within eukaryotic cells in the mitochondrial matrix, but is encoded by nuclear DNA rather than mitochondrial. It is synthesized using cytoplasmic ribosomes, then transported into the mitochondrial matrix.
Ketogenesis is the biochemical process through which organisms produce ketone bodies by breaking down fatty acids and ketogenic amino acids. [1] [2] The process supplies energy to certain organs, particularly the brain, heart and skeletal muscle, under specific scenarios including fasting, caloric restriction, sleep, [3] or others.
After four months of experimental works to fill in the gaps, Krebs and Johnson succeeded in establishing the sequence of the chemical cycle, which they called the "citric acid cycle". [32] [33] It is also known as the "Krebs cycle" or "tricarboxylic acid (TCA) cycle". Krebs sent a short manuscript account of the discovery to Nature on 10 June ...