Selective conversion of plasma glucose into CO 2 by Saccharomyces cerevisiae for the measurement of 13 C abundance by isotope ratio mass spectrometry: proof of principle

To study carbohydrate digestion and glucose absorption, time‐dependent 13 C enrichment in plasma glucose is measured after oral administration of naturally occurring 13 C‐enriched carbohydrates. The isotope enrichment of the administered carbohydrate is low (APE <0.1%) and plasma 13 C glucose measurements are routinely determined with gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) or liquid chromatography/combustion/isotope ratio mass spectrometry (LC/C/IRMS). In this study, plasma glucose was converted into CO 2 by an in‐tube reaction with yeast permitting direct measurement of 13 CO 2 in the headspace. Saccharomyces cerevisiae incubated under anaerobic conditions was able to convert sufficient glucose into CO 2 to produce a consistent CO 2 peak in IRMS with little variation in peak area and precise δ 13 C PDB values for corn glucose: −11.40 ± 0.16‰, potato glucose: −25.17 ± 0.13‰, and plasma glucose: −26.29 ± 0.05‰. The measurement showed high linearity (R 2  = 0.999) and selectivity and was not affected by the glucose concentration in the tested range of 5–15 mM. Comparison with GC/C/IRMS showed a good correlation of enrichment data: R 2  > 0.98 for both sources of glucose and plasma samples. Commercially available, instant dried baker's yeast was qualitatively and quantitatively comparable with freshly prepared yeast: R 2  > 0.96, slope 1.03 and 1.08 for glucose solutions and plasma, respectively. Thus, yeast conversion of plasma glucose into CO 2 and 13 C measurement applying a breath 13 CO 2 analyzer is an inexpensive, simple and equally accurate alternative to the more expensive and laborious GC/C/IRMS and LC/C/IRMS measurements. Copyright © 2007 John Wiley & Sons, Ltd.