Fermentation is primarily defined as the chemical conversion of carbohydrates into alcohols or acids, with sugar being the main substrate. This process is not applicable to proteins and fats, as fatty acids are metabolized into acetyl-CoA, which requires the Krebs cycle that operates only in the presence of oxygen. Similarly, amino acids are typically broken down into Krebs cycle intermediates, also necessitating oxygen for metabolism. While some amino acids can be converted into oxaloacetate or pyruvate, it remains unclear if these conversions occur anaerobically. A broader definition of fermentation includes the facilitation of chemical reactions involving organic compounds without oxygen. Notably, amino acids can undergo fermentation through processes like Stickland Fermentation, where one amino acid acts as an electron donor and another as an electron receptor, a method likely utilized by anaerobic bacteria.
