Browsing by Subject "on-line monitoring"

Brewer's yeasts metabolize sugars and produce ethanol and CO2. This study aimed to investigate the relation between the assimilation of sugars in all-malt wort and isotopic signature of carbon and oxygen in the evolved CO2 from brewery fermentations. The isotopic composition of CO2 was measured by a tunable diode laser absorption spectrometer. The isotopic data obtained with automatic sampling, on-line, and in real-time. Wort samples were collected with 3 h intervals to quantify the residual sugars by high-performance liquid chromatography. Patterns of changes in δ13C and δ18O values were unique to experiments with each yeast type. The common overall ascending trend in δ13C and δ18O values in all experiments can be described by kinetic fractionation of isotopes, which explains that in a bioreaction the lighter isotopes participate in the reaction more readily than the heavier ones. Therefore, the early emergence of light isotopologues of CO2 may be a consequence of the fermentation of light isotopologues of sugars. A sudden decrease and then increase in delta values were observed in all experiments before the residual concentrations of glucose and fructose reach their lowest levels. This can be an indicator of the complete assimilation of monosaccharides by yeast. In the fermentations that yeast was able to consume maltose, δ13C and δ18O values raised considerably in a short period. Concurrently, maltose approached its eventual residual concentrations indicating an endpoint for its utilization by yeast. Our results confirm the hypothesis of a connection between the assimilation of sugars and the isotopic signature of evolved CO2 during brewery fermentations. The findings support the potential of off-gas isotopic analysis to monitor sugar assimilation in brewery fermentations.