Development of a new method for evaluation of yeast vitality by measuring intracellular pH.

Imai, T., Nakajima, I. and Ohno, T.

Abstract
It has been very difficult to accurately assess subtle differences in cell vitality in practical brewing circumstances. A sufficiently sensitive method was developed by measuring intracellular pII (proton pump activity) which plays an important role in yeast growth and fermentation. In order to measure proton extrusion from brewer's yeast under physiological conditions, a method of measuring intracellular pII at low pII was devised. This new method was named the ICP (intracelluar pII) method for short. The intracellular pII of brewer's yeast was measured using a fluorescent reagent and a spectrofluorophotometer. Investigations including the comparison with acidification power test were carried out. As a result, this method turned out to be able to assess subtle differences of vitality of yeast cells which appear in practical brewing conditions.
Keywords : brewers' yeast fluorescence measurement pH physiology staining