Use of Immunofluorescence and Viability Stains in Quality Control

Abstract

Immunofluorescence has been evaluated as a rapid quality control technique for the detection of low levels of wild yeasts in culture yeast or other brewery samples. Antisera have been prepared against antigenic groups A to F, pooled and absorbed with culture yeast. Using the indirect staining method and fluorescein isothiocyanate or rhodamine as fluorochrome, levels as low as 10 wild yeasts per million cells can be detected in three hours. Combined immunofluorescence and viability staining allows the differentiation of live and dead, culture and wild yeast cells, on the same slide by alternating the light sources. The preferred method uses fluorescein isothiocyanate, excited by incident blue light, for wild yeast detection, combined with methylene blue, viewed by transmitted light, for viability differentiation. Fluorescein diacetate is a useful viability stain for yeasts although agreement between results comparing it with methylene blue and slide culture viabilities is not exact for heat-stressed cells. Some nonbrewing yeasts require heating for two minutes at 50° C before consistent results are obtained with fluorescein diacetate. An examination of the mechanism of the action of methylene blue as a viability stain has suggested that the action is one of permeability, rather than permeability followed by enzymatic reduction.