Assessment of the Physiological Status of Yeast During High- and Low-Gravity Wort Fermentations Determined by Flow Cytometry

摘要

The use of flow cytometry as an analytical control tool during high-gravity (20°P) and low-gravity (12°P) wort fermentations was investigated. A flow cytometer is an instrument capable of determining the physiological status of Saccharomyces cerevisiae cultures in near real time. Flow cytometry uses technology that simultaneously performs multiparametric analyses of the physical and chemical characteristics of the yeast based on cell size, relative granularity, and fluorescence. The differentiation of subpopulations permitted the classification of viable and depleted cell populations. Flow cytometry and fluorescent dyes provided a rapid and accurate means to monitor the viability and vitality of yeast throughout fermentation. The viability method distinguished between dead, live, and damaged cells. Propidium iodide and fluores-cein diacetate probes were used as markers to determine functioning cells. The vitality of the cells was determined based on their intracel-lular pH using the pH-dependent fluorescent probe carboxy SNARF-4F (SNARF). The SNARF possesses two inversely related emission signals at two different wavelengths, which made it possible to calculate the pH from the ratio between the fluorescence intensities measured at the two wavelengths. Predictors of yeast performance such as intracellular glycogen and trehalose concentrations, assayed by flow cytometry, were established. The results indicate that flow cytometry provides an innovative, rapid, and viable option for brewers to evaluate yeast cells during fermentation.