Critical evaluation of sampling techniques for residual glucose determination in carbon‐limited chemostat culture of Saccharomyces cerevisiae

In this paper, three sampling techniques for rapid quenching of cellular metabolism and subsequent separation of cells from fermentation broth are compared: (i) quick freezing of fermentation broth directly in liquid nitrogen; (ii) quenching metabolism by exposing the fermentation broth to stainless steel beads (4‐mm diameter) in a filter syringe precooled to −18°C; and (iii) withdrawal of the filtrate through a 0.45‐μm filter attached to a syringe and a needle inserted directly into the fermentor. It was concluded that use of liquid nitrogen as a quenching method to rapidly arrest cellular metabolism, for quantitative analysis of extracellular glucose, is not a very reliable method and that the filter syringe steel beads work very well. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 395–399, 2003.