A Novel and Rapid Method for Yeast Vitality Evaluation Based on the Methylene Blue Dye Reduction Test

Abstract

Variation in the quality of yeast is one of the major factors that causes irregularity in fermentation. Yeast quality needs to be estimated accurately to maintain product quality. In the past, several methods for measuring yeast vitality have been proposed. However, these methods have not been widely used in spiked programs for yeast vitality because they show low sensitivity and little correlation with fermentation performance. In this paper, a novel method of evaluating yeast vitality based on the methylene blue dye reduction test (MBRT) is studied. The method is further developed and standardized by measuring varied yeast vitality, and a T½ value is used to estimate yeast vitality. The data demonstrate that MBRT can be used to rapidly and accurately evaluate yeast vitality. T½ values of 0 to 100 sec signify a highly active yeast with good physiological state, while T½ values of 100 to 250 sec indicate reduced metabolic activity and T½ values of more than 250 sec indicate low metabolic competence that could result in sluggish fermentation. This is the first report of the use of quantification of the decoloration rate to measure yeast vitality. The assay could be extended to other applications that involve cell quality.