Detection of mannan from Saccharomyces cerevisiae by flow cytometry

Mannan plays an important role in the formation of some beer hazes. The effects of mechanical agitation of Saccharomyces cerevisiae brewing strains and subsequent impact on beer quality were investigated. Six different brewing yeast strains (ale and lager) were subjected to mechanical agitation in a temperature-controlled bioreactor. As a result of this study, a protocol is described for the determination of mannan residues from S. cerevisiae cells in nearly real time. Flow cytometric methods permitted the quantitative analysis of mannan residues based on particle size, relative granularity, and florescence intensity. The mannan concentrations and optical density of its supernatant increased as the yeast slurry was agitated. It was concluded that hydrodynamic stresses from agitation of yeast slurries cause mannan, an unfilterable haze constituent, to be released from the yeast cell wall. Furthermore, flow cytometry provides an innovative, rapid, and viable option for quantifying the influence that beer processing conditions have on beer stability.