GAS-CHROMATOGRAPHIC DETERMINATION OF VOLATILE FATTY-ACIDS IN 80-PERCENT ETHANOL

A modification of the method of short chain fatty acid (VFA) determina tion by gas chromatographic analysis originally described by JOUANY (1 982) is proposed. This adaptation, involving changes in chromatographi c conditions, allows VFA to be quantified in 80% ethanol solution. Coe fficients of variation, calculated from repeated analysis of a standar d solution, were generally lower than 6%. Relations between actual and theoretical concentrations illustrated the accuracy of the method. An alysis of ethanolic samples from different fermentation media produces similar results to the original method for acetic, propionic and buty ric acids (major VFAs) and for total VFA. These comparative analyses s howed the low sensitivity of the proposed method for isobutyric, valer ic and isovaleric acids (minor VFAs); this probably results from the d ilution due to ethanol addition. VFA preservation in 80% ethanol solut ion is confirmed over a period of up to 2 months. Although samples wer e highly diluted by ethanol addition, the method of VFA determination in alcohol solutions allows for the exact quantification of fermentati on products and of unfermented polysaccharides, from the same fermenta tion slurry, treated in a single step.