The supernatant water sample used for the validation of the method was derived from the natural fermentation of cassava starch at room temperature (ranging from 21.5 to 31.0 C) for
32 days, when it reached the plateau acidity of 2.0 mL of NaOH 0.1 mol/L for each aliquot of 10 mL (Marcon et al., 2006). The sample was kept frozen until the time of analysis. Due to the impossibility of obtaining samples of free organic acids and the high concentration of acetic and butyric acids in the sample, a 50-fold dilution of the sample was obtained with ultrapure water for the evaluation of the precision and accuracy validation parameters, while for lactic and propionic acids the dilution was 2-fold.