... other, its mirror image, is D-(-)-lactic acid or (R)-lactic acid. L-(+)-Lactic acid is the biologically important isomer. In animals, ... over 20 mmol/L during intense exertion. Industrially, lactic acid fermentation is performed by Lactobacillus bacteria, among others. These ... fermented from lactose (milk sugar), most commercially used lactic acid is derived by using bacteria such as Bacillus acidilacti, ...