【Reading】にゅうさん

【English Name】Lactic Acid

Lactic acid is an organic acid belonging to the class of hydroxy acids, with the molecular formula C₃H₆O₃. Its systematic name is 2-hydroxypropanoic acid (IUPAC nomenclature). Because it has an asymmetric carbon, the optical isomers of the L-form and D-form arise, and in nature the L-form predominates.

In the world of sushi, lactic acid is an indispensable compound. In fermented sushi such as narezushi, lactic acid fermentation, in which lactic acid bacteria act on sugars to produce lactic acid, lowers the pH, suppressing the growth of spoilage bacteria and improving preservability. This mechanism is the core technology of narezushi, regarded as the origin of sushi, and also the historical starting point leading to modern haya-zushi (quick sushi).

Lactic acid bacteria are active in the production of a wide variety of foods, including yogurt, cheese and pickles. In sake brewing, in the kimoto method the lactic acid produced by lactic acid bacteria works to suppress unwanted microbes, whereas in the sokujo-moto method, lactic acid is added directly from the early stage of brewing. The latter is advantageous in production efficiency, but the complex flavors born during fermentation are said to be hard to reproduce.

Incidentally, lactic acid was long widely believed to be the substance causing muscle fatigue, but since research from 2001 onward, counterevidence to this conventional view has been presented, and revision of the understanding is now progressing.