MONITORING OF FERMENTATION BY INFRARED SPECTROMETRY - ALCOHOLIC AND LACTIC FERMENTATIONS

Infrared spectrometry offers a great potential for quantitative analys is of substrates and products in fermentation media. Like this, a rapi d measurement of lactose, galactose and lactic acid during lactic ferm entation and sugars (glucose and fructose), glycerol and ethanol durin g alcoholic fermentation will constitute a major progress for the moni toring and the control of these processes. The samples, taken manually during the fermentations, permitted the determination of the interest ing spectral ranges for the measurement of these compounds. These rang es, characterized by significant evolutions of absorbance, are situate d in the middle infrared zone: between 1100 and 1040 cm-1 for lactose and galactose, between 1593 and 1515 cm-1 for lactate, between 1206 an d 1026 cm-1 for molecules of the alcoholic fermentation and between 30 00 and 1026 cm-1 for ethanol. Calibration is realized by the partial l east-squares method from representative samples of the studied concent rations. The regression coefficients of the correlation between the co ncentrations measured by infrared spectrometry and liquid chromatograp hy are better than 0.99. The maximum standard errors are 0.46, 0.57 an d 0.95 g l-1 respectively for lactose, galactose and lactic acid; 2.5, 0.09 and 0.98 g l-1, respectively for the sugars, glycerol and ethano l.